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1.  Relationships between starch synthase I and branching enzyme isozymes determined using double mutant rice lines 
BMC Plant Biology  2014;14:80.
Starch is the most important carbohydrate in plant storage tissues. Multiple isozymes in at least four enzyme classes are involved in starch biosynthesis. Some of these isozymes are thought to interact and form complexes for efficient starch biosynthesis. Of these enzyme classes, starch synthases (SSs) and branching enzymes (BEs) play particularly central roles.
We generated double mutant lines (ss1/be1 and ss1 L /be2b) between SSI (the largest component of total soluble SS activity) and BEI or BEIIb (major BEs in developing rice endosperm) to explore the relationships among these isozymes. The seed weight of ss1/be1 was comparable to that of wild type, although most ss1/be2b seeds were sterile and no double recessive plants were obtained. The seed weight of the double recessive mutant line ss1 L /be2b, derived from the leaky ss1 mutant (ss1 L ) and be2b, was higher than that of the single be2b mutant. Analyses of the chain-length distribution of amylopectin in ss1/be1 endosperm revealed additive effects of SSI and BEI on amylopectin structure. Chain-length analysis indicated that the BEIIb deficiency significantly reduced the ratio of short chains in amylopectin of ss1 L /be2b. The amylose content of endosperm starch of ss1/be1 and ss1 L /be2b was almost the same as that of wild type, whereas the endosperm starch of be2b contained more amylose than did that of wild type. SSI, BEI, and BEIIb deficiency also affected the extent of binding of other isozymes to starch granules.
Analysis of the chain-length distribution in amylopectin of the double mutant lines showed that SSI and BEI or BEIIb primarily function independently, and branching by BEIIb is followed by SSI chain elongation. The increased amylose content in be2b was because of reduced amylopectin biosynthesis; however, the lower SSI activity in this background may have enhanced amylopectin biosynthesis as a result of a correction of imbalance between the branching and elongation found in the single mutant. The fact that a deficiency of SSI, BEI, or BEIIb affected the affinity of other starch biosynthetic isozymes for the starch granule implies that there is a close interaction among SSI, BEI and BEIIb during amylopectin biosynthesis in rice endosperm.
PMCID: PMC3976638  PMID: 24670252
Amylopectin; Amylose; Branching enzyme; Mutant; Rice; Starch synthase
2.  Genomic rearrangements and signatures of breeding in the allo-octoploid strawberry as revealed through an allele dose based SSR linkage map 
BMC Plant Biology  2014;14:55.
Breeders in the allo-octoploid strawberry currently make little use of molecular marker tools. As a first step of a QTL discovery project on fruit quality traits and resistance to soil-borne pathogens such as Phytophthora cactorum and Verticillium we built a genome-wide SSR linkage map for the cross Holiday x Korona. We used the previously published MADCE method to obtain full haplotype information for both of the parental cultivars, facilitating in-depth studies on their genomic organisation.
The linkage map incorporates 508 segregating loci and represents each of the 28 chromosome pairs of octoploid strawberry, spanning an estimated length of 2050 cM. The sub-genomes are denoted according to their sequence divergence from F. vesca as revealed by marker performance. The map revealed high overall synteny between the sub-genomes, but also revealed two large inversions on LG2C and LG2D, of which the latter was confirmed using a separate mapping population. We discovered interesting breeding features within the parental cultivars by in-depth analysis of our haplotype data. The linkage map-derived homozygosity level of Holiday was similar to the pedigree-derived inbreeding level (33% and 29%, respectively). For Korona we found that the observed homozygosity level was over three times higher than expected from the pedigree (13% versus 3.6%). This could indicate selection pressure on genes that have favourable effects in homozygous states. The level of kinship between Holiday and Korona derived from our linkage map was 2.5 times higher than the pedigree-derived value. This large difference could be evidence of selection pressure enacted by strawberry breeders towards specific haplotypes.
The obtained SSR linkage map provides a good base for QTL discovery. It also provides the first biologically relevant basis for the discernment and notation of sub-genomes. For the first time, we revealed genomic rearrangements that were verified in a separate mapping population. We believe that haplotype information will become increasingly important in identifying marker-trait relationships and regions that are under selection pressure within breeding material. Our attempt at providing a biological basis for the discernment of sub-genomes warrants follow-up studies to streamline the naming of the sub-genomes among different octoploid strawberry maps.
PMCID: PMC3944823  PMID: 24581289
Genomic rearrangement; Inversion; Fragaria; Polyploid; Haplotype; Homozygosity; MAS; Selection; Breeding signature
3.  Quantitative trait loci affecting reproductive phenology in peach 
BMC Plant Biology  2014;14:52.
The reproductive phenology of perennial plants in temperate climates is largely conditioned by the duration of bud dormancy, and fruit developmental processes. Bud dormancy release and bud break depends on the perception of cumulative chilling and heat during the bud development. The objective of this work was to identify new quantitative trait loci (QTLs) associated to temperature requirements for bud dormancy release and flowering and to fruit harvest date, in a segregating population of peach.
We have identified QTLs for nine traits related to bud dormancy, flowering and fruit harvest in an intraspecific hybrid population of peach in two locations differing in chilling time accumulation. QTLs were located in a genetic linkage map of peach based on single nucleotide polymorphism (SNP) markers for eight linkage groups (LGs) of the peach genome sequence. QTLs for chilling requirements for dormancy release and blooming clustered in seven different genomic regions that partially coincided with loci identified in previous works. The most significant QTL for chilling requirements mapped to LG1, close to the evergrowing locus. QTLs for heat requirement related traits were distributed in nine genomic regions, four of them co-localizing with QTLs for chilling requirement trait. Two major loci in LG4 and LG6 determined fruit harvest time.
We identified QTLs associated to nine traits related to the reproductive phenology in peach. A search of candidate genes for these QTLs rendered different genes related to flowering regulation, chromatin modification and hormone signalling. A better understanding of the genetic factors affecting crop phenology might help scientists and breeders to predict changes in genotype performance in a context of global climate change.
PMCID: PMC3941940  PMID: 24559033
Prunus persica; Bud dormancy; Chilling requirement; Heat requirement; Flowering; Fruit maturation; QTL
4.  Pyramiding, alternating or mixing: comparative performances of deployment strategies of nematode resistance genes to promote plant resistance efficiency and durability 
BMC Plant Biology  2014;14:53.
Resistant cultivars are key elements for pathogen control and pesticide reduction, but their repeated use may lead to the emergence of virulent pathogen populations, able to overcome the resistance. Increased research efforts, mainly based on theoretical studies, explore spatio-temporal deployment strategies of resistance genes in order to maximize their durability. We evaluated experimentally three of these strategies to control root-knot nematodes: cultivar mixtures, alternating and pyramiding resistance genes, under controlled and field conditions over a 3-years period, assessing the efficiency and the durability of resistance in a protected crop rotation system with pepper as summer crop and lettuce as winter crop.
The choice of the resistance gene and the genetic background in which it is introgressed, affected the frequency of resistance breakdown. The pyramiding of two different resistance genes in one genotype suppressed the emergence of virulent isolates. Alternating different resistance genes in rotation was also efficient to decrease virulent populations in fields due to the specificity of the virulence and the trapping effect of resistant plants. Mixing resistant cultivars together appeared as a less efficient strategy to control nematodes.
This work provides experimental evidence that, in a cropping system with seasonal sequences of vegetable species, pyramiding or alternating resistance genes benefit yields in the long-term by increasing the durability of resistant cultivars and improving the long-term control of a soil-borne pest. To our knowledge, this result is the first one obtained for a plant-nematode interaction, which helps demonstrate the general applicability of such strategies for breeding and sustainable management of resistant cultivars against pathogens.
PMCID: PMC3944934  PMID: 24559060
Breeding strategy; Capsicum spp; Meloidogyne spp; Resistance gene deployment; Root-knot nematodes; Sustainable crop protection; Virulence emergence
5.  Manipulating cinnamyl alcohol dehydrogenase (CAD) expression in flax affects fibre composition and properties 
BMC Plant Biology  2014;14:50.
In recent decades cultivation of flax and its application have dramatically decreased. One of the reasons for this is unpredictable quality and properties of flax fibre, because they depend on environmental factors, retting duration and growing conditions. These factors have contribution to the fibre composition, which consists of cellulose, hemicelluloses, lignin and pectin. By far, it is largely established that in flax, lignin reduces an accessibility of enzymes either to pectin, hemicelluloses or cellulose (during retting or in biofuel synthesis and paper production).
Therefore, in this study we evaluated composition and properties of flax fibre from plants with silenced CAD (cinnamyl alcohol dehydrogenase) gene, which is key in the lignin biosynthesis. There is evidence that CAD is a useful tool to improve lignin digestibility and/or to lower the lignin levels in plants.
Two studied lines responded differentially to the introduced modification due to the efficiency of the CAD silencing. Phylogenetic analysis revealed that flax CAD belongs to the “bona-fide” CAD family. CAD down-regulation had an effect in the reduced lignin amount in the flax fibre cell wall and as FT-IR results suggests, disturbed lignin composition and structure. Moreover introduced modification activated a compensatory mechanism which was manifested in the accumulation of cellulose and/or pectin. These changes had putative correlation with observed improved fiber’s tensile strength. Moreover, CAD down-regulation did not disturb at all or has only slight effect on flax plants’ development in vivo, however, the resistance against flax major pathogen Fusarium oxysporum decreased slightly. The modification positively affected fibre possessing; it resulted in more uniform retting.
The major finding of our paper is that the modification targeted directly to block lignin synthesis caused not only reduced lignin level in fibre, but also affected amount and organization of cellulose and pectin. However, to conclude that all observed changes are trustworthy and correlated exclusively to CAD repression, further analysis of the modified plants genome is necessary. Secondly, this is one of the first studies on the crop from the low-lignin plants from the field trail which demonstrates that such plants could be successfully cultivated in a field.
PMCID: PMC3945063  PMID: 24552628
Cinnamyl alcohol dehydrogenase (CAD); Lignin; Cell wall; Flax fibre; Linum usitatissimum; L
6.  Genetic and biochemical differences in populations bred for extremes in maize grain methionine concentration 
BMC Plant Biology  2014;14:49.
Methionine is an important nutrient in animal feed and several approaches have been developed to increase methionine concentration in maize (Zea mays L.) grain. One approach is through traditional breeding using recurrent selection. Using divergent selection, genetically related populations with extreme differences in grain methionine content were produced. In order to better understand the molecular mechanisms controlling grain methionine content, we examined seed proteins, transcript levels of candidate genes, and genotypes of these populations.
Two populations were selected for high or low methionine concentration for eight generations and 40 and 56% differences between the high and low populations in grain methionine concentration were observed. Mean values between the high and low methionine populations differed by greater than 1.5 standard deviations in some cycles of selection. Other amino acids and total protein concentration exhibited much smaller changes. In an effort to understand the molecular mechanisms that contribute to these differences, we compared transcript levels of candidate genes encoding high methionine seed storage proteins involved in sulfur assimilation or methionine biosynthesis. In combination, we also explored the genetic mechanisms at the SNP level through implementation of an association analysis. Significant differences in methionine-rich seed storage protein genes were observed in comparisons of high and low methionine populations, while transcripts of seed storage proteins lacking high levels of methionine were unchanged. Seed storage protein levels were consistent with transcript levels. Two genes involved in sulfur assimilation, Cys2 and CgS1 showed substantial differences in allele frequencies when two selected populations were compared to the starting populations. Major genes identified across cycles of selection by a high-stringency association analysis included dzs18, wx, dzs10, and zp27.
We hypothesize that transcriptional changes alter sink strength by altering the levels of methionine-rich seed storage proteins. To meet the altered need for sulfur, a cysteine-rich seed storage protein is altered while sulfur assimilation and methionine biosynthesis throughput is changed by selection for certain alleles of Cys2 and CgS1.
PMCID: PMC3946590  PMID: 24552611
Methionine; Breeding; Association mapping; Sulfur assimilation; Storage proteins
7.  ENHANCING CTR1-10 ETHYLENE RESPONSE2 is a novel allele involved in CONSTITUTIVE TRIPLE-RESPONSE1-mediated ethylene receptor signaling in Arabidopsis 
BMC Plant Biology  2014;14:48.
The signal output of ethylene receptor family members is mediated by unknown mechanisms to activate the Raf-like protein CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) in negatively regulating ethylene signaling. The physical interaction between the ethylene receptor histidine kinase (HK) domain and CTR1 N terminus is essential to the CTR1-mediated receptor signal output. To advance our knowledge of the involvement of CTR1-mediated ethylene receptor signaling, we performed a genetic screen for mutations that enhanced the constitutive ethylene response in the weak ctr1-10 allele.
We isolated a loss-of-function allele of ENHANCING ctr1-10 ETHYLENE RESPONSE2 (ECR2) and found that ecr2-1 ctr1-10 and the strong allele ctr1-1 conferred a similar, typical constitutive ethylene response phenotype. Genetic analyses and transformation studies suggested that ECR2 acts downstream of the ethylene receptors and upstream of the transcription factors ETHYLENE INSENSITIVE3 (EIN3) and EIN3-LIKE1 (EIL1), which direct the expression of ethylene response genes. Signal output by the N terminus of the ethylene receptor ETHYLENE RESPONSE1 (ETR1) can be mediated by a pathway independent of CTR1. Expression of the N terminus of the ethylene-insensitive etr1-1 but not the full-length isoform rescued the ecr2-1 ctr1-10 phenotype, which indicates the involvement of ECR2 in CTR1-mediated but not -independent, ethylene receptor signaling. ECR2 was mapped to the centromere region on chromosome 2. With incomplete sequence and annotation information and rare chromosome recombination events in this region, the cloning of ECR2 is challenging and still in progress.
ECR2 is a novel allele involved in the ethylene receptor signaling that is mediated by CTR1. CTR1 activation by ethylene receptors may require ECR2 for suppressing the ethylene response.
PMCID: PMC3933193  PMID: 24529183
Arabidopsis; Ethylene signaling; CTR1; ETR1; ECR2
8.  A systems-wide comparison of red rice (Oryza longistaminata) tissues identifies rhizome specific genes and proteins that are targets for cultivated rice improvement 
BMC Plant Biology  2014;14:46.
The rhizome, the original stem of land plants, enables species to invade new territory and is a critical component of perenniality, especially in grasses. Red rice (Oryza longistaminata) is a perennial wild rice species with many valuable traits that could be used to improve cultivated rice cultivars, including rhizomatousness, disease resistance and drought tolerance. Despite these features, little is known about the molecular mechanisms that contribute to rhizome growth, development and function in this plant.
We used an integrated approach to compare the transcriptome, proteome and metabolome of the rhizome to other tissues of red rice. 116 Gb of transcriptome sequence was obtained from various tissues and used to identify rhizome-specific and preferentially expressed genes, including transcription factors and hormone metabolism and stress response-related genes. Proteomics and metabolomics approaches identified 41 proteins and more than 100 primary metabolites and plant hormones with rhizome preferential accumulation. Of particular interest was the identification of a large number of gene transcripts from Magnaportha oryzae, the fungus that causes rice blast disease in cultivated rice, even though the red rice plants showed no sign of disease.
A significant set of genes, proteins and metabolites appear to be specifically or preferentially expressed in the rhizome of O. longistaminata. The presence of M. oryzae gene transcripts at a high level in apparently healthy plants suggests that red rice is resistant to this pathogen, and may be able to provide genes to cultivated rice that will enable resistance to rice blast disease.
PMCID: PMC3933257  PMID: 24521476
Transcriptomics; Proteomics; Metabolomics; Rhizome; Invasive species; Disease resistance; Rice blast; Rice
9.  Assembly and analysis of a male sterile rubber tree mitochondrial genome reveals DNA rearrangement events and a novel transcript 
BMC Plant Biology  2014;14:45.
The rubber tree, Hevea brasiliensis, is an important plant species that is commercially grown to produce latex rubber in many countries. The rubber tree variety BPM 24 exhibits cytoplasmic male sterility, inherited from the variety GT 1.
We constructed the rubber tree mitochondrial genome of a cytoplasmic male sterile variety, BPM 24, using 454 sequencing, including 8 kb paired-end libraries, plus Illumina paired-end sequencing. We annotated this mitochondrial genome with the aid of Illumina RNA-seq data and performed comparative analysis. We then compared the sequence of BPM 24 to the contigs of the published rubber tree, variety RRIM 600, and identified a rearrangement that is unique to BPM 24 resulting in a novel transcript containing a portion of atp9.
The novel transcript is consistent with changes that cause cytoplasmic male sterility through a slight reduction to ATP production efficiency. The exhaustive nature of the search rules out alternative causes and supports previous findings of novel transcripts causing cytoplasmic male sterility.
PMCID: PMC3925788  PMID: 24512148
Rubber tree; Hevea brasiliensis; Mitochondria; Cytoplasmic male sterility; Genome sequencing
10.  EsDREB2B, a novel truncated DREB2-type transcription factor in the desert legume Eremosparton songoricum, enhances tolerance to multiple abiotic stresses in yeast and transgenic tobacco 
BMC Plant Biology  2014;14:44.
Dehydration-Responsive Element-Binding Protein2 (DREB2) is a transcriptional factor which regulates the expression of several stress-inducible genes. DREB2-type proteins are particularly important in plant responses to drought, salt and heat. DREB2 genes have been identified and characterized in a variety of plants, and DREB2 genes are promising candidate genes for the improvement of stress tolerance in plants. However, little is known about these genes in plants adapted to water-limiting environments.
In this study, we describe the characterization of EsDREB2B, a novel DREB2B gene identified from the desert plant Eremosparton songoricum. Phylogenetic analysis and motif prediction indicate that EsDREB2B encodes a truncated DREB2 polypeptide that belongs to a legume-specific DREB2 group. In E. songoricum, EsDREB2B transcript accumulation was induced by a variety of abiotic stresses, including drought, salinity, cold, heat, heavy metal, mechanical wounding, oxidative stress and exogenous abscisic acid (ABA) treatment. Consistent with the predicted role as a transcription factor, EsDREB2B was targeted to the nucleus of onion epidermal cells and exhibited transactivation activity of a GAL4-containing reporter gene in yeast. In transgenic yeast, overexpression of EsDREB2B increased tolerance to multiple abiotic stresses. Our findings indicate that EsDREB2B can enhance stress tolerance in other plant species. Heterologous expression of EsDREB2B in tobacco showed improved tolerance to multiple abiotic stresses, and the transgenic plants exhibited no reduction in foliar growth. We observed that EsDREB2B is a functional DREB2-orthologue able to influence the physiological and biochemical response of transgenic tobacco to stress.
Based upon these findings, EsDREB2B encodes an abiotic stress-inducible, transcription factor which confers abiotic stress-tolerance in yeast and transgenic tobacco.
PMCID: PMC3940028  PMID: 24506952
Cold; DREB; Drought; Heat; Proline; Salt; Stress; Transcript accumulation; Transgenic tobacco
11.  Genetic analysis of safflower domestication 
BMC Plant Biology  2014;14:43.
Safflower (Carthamus tinctorius L.) is an oilseed crop in the Compositae (a.k.a. Asteraceae) that is valued for its oils rich in unsaturated fatty acids. Here, we present an analysis of the genetic architecture of safflower domestication and compare our findings to those from sunflower (Helianthus annuus L.), an independently domesticated oilseed crop within the same family.
We mapped quantitative trait loci (QTL) underlying 24 domestication-related traits in progeny from a cross between safflower and its wild progenitor, Carthamus palaestinus Eig. Also, we compared QTL positions in safflower against those that have been previously identified in cultivated x wild sunflower crosses to identify instances of colocalization.
We mapped 61 QTL, the vast majority of which (59) exhibited minor or moderate phenotypic effects. The two large-effect QTL corresponded to one each for flower color and leaf spininess. A total of 14 safflower QTL colocalized with previously reported sunflower QTL for the same traits. Of these, QTL for three traits (days to flower, achene length, and number of selfed seed) had cultivar alleles that conferred effects in the same direction in both species.
As has been observed in sunflower, and unlike many other crops, our results suggest that the genetics of safflower domestication is quite complex. Moreover, our comparative mapping results indicate that safflower and sunflower exhibit numerous instances of QTL colocalization, suggesting that parallel trait transitions during domestication may have been driven, at least in part, by parallel genotypic evolution at some of the same underlying genes.
PMCID: PMC3925122  PMID: 24502326
Carthamus; Domestication; Comparative genetic mapping; Helianthus; Parallel evolution; QTL analysis; Safflower; Sunflower
12.  The C-terminal propeptide of a plant defensin confers cytoprotective and subcellular targeting functions 
BMC Plant Biology  2014;14:41.
Plant defensins are small (45–54 amino acids), basic, cysteine-rich proteins that have a major role in innate immunity in plants. Many defensins are potent antifungal molecules and are being evaluated for their potential to create crop plants with sustainable disease resistance. Defensins are produced as precursor molecules which are directed into the secretory pathway and are divided into two classes based on the absence (class I) or presence (class II) of an acidic C-terminal propeptide (CTPP) of about 33 amino acids. The function of this CTPP had not been defined.
By transgenically expressing the class II plant defensin NaD1 with and without its cognate CTPP we have demonstrated that NaD1 is phytotoxic to cotton plants when expressed without its CTPP. Transgenic cotton plants expressing constructs encoding the NaD1 precursor with the CTPP had the same morphology as non-transgenic plants but expression of NaD1 without the CTPP led to plants that were stunted, had crinkled leaves and were less viable. Immunofluorescence microscopy and transient expression of a green fluorescent protein (GFP)-CTPP chimera were used to confirm that the CTPP is sufficient for vacuolar targeting. Finally circular dichroism and NMR spectroscopy were used to show that the CTPP adopts a helical confirmation.
In this report we have described the role of the CTPP on NaD1, a class II defensin from Nicotiana alata flowers. The CTPP of NaD1 is sufficient for vacuolar targeting and plays an important role in detoxification of the defensin as it moves through the plant secretory pathway. This work may have important implications for the use of defensins for disease protection in transgenic crops.
PMCID: PMC3922462  PMID: 24495600
Plant defensin; Phytotoxicity; Vacuolar targeting; Transgenic cotton
13.  Sodium hydrosulfide induces systemic thermotolerance to strawberry plants through transcriptional regulation of heat shock proteins and aquaporin 
BMC Plant Biology  2014;14:42.
Temperature extremes represent an important limiting factor to plant growth and productivity. The present study evaluated the effect of hydroponic pretreatment of strawberry (Fragaria x ananassa cv. ‘Camarosa’) roots with an H2S donor, sodium hydrosulfide (NaHS; 100 μM for 48 h), on the response of plants to acute heat shock treatment (42°C, 8 h).
Heat stress-induced phenotypic damage was ameliorated in NaHS-pretreated plants, which managed to preserve higher maximum photochemical PSII quantum yields than stressed plants. Apparent mitigating effects of H2S pretreatment were registered regarding oxidative and nitrosative secondary stress, since malondialdehyde (MDA), H2O2 and nitric oxide (NO) were quantified in lower amounts than in heat-stressed plants. In addition, NaHS pretreatment preserved ascorbate/glutathione homeostasis, as evidenced by lower ASC and GSH pool redox disturbances and enhanced transcription of ASC (GDH) and GSH biosynthetic enzymes (GS, GCS), 8 h after heat stress imposition. Furthermore, NaHS root pretreatment resulted in induction of gene expression levels of an array of protective molecules, such as enzymatic antioxidants (cAPX, CAT, MnSOD, GR), heat shock proteins (HSP70, HSP80, HSP90) and aquaporins (PIP).
Overall, we propose that H2S root pretreatment activates a coordinated network of heat shock defense-related pathways at a transcriptional level and systemically protects strawberry plants from heat shock-induced damage.
PMCID: PMC3933230  PMID: 24499299
Ascorbic acid; Heat shock proteins; Hydrogen sulfide; Nitrosative stress; Oxidative stress; Priming; Thermotolerance; Fragaria x ananassa
14.  Characterization of the glutathione S-transferase gene family through ESTs and expression analyses within common and pigmented cultivars of Citrus sinensis (L.) Osbeck 
BMC Plant Biology  2014;14:39.
Glutathione S-transferases (GSTs) represent a ubiquitous gene family encoding detoxification enzymes able to recognize reactive electrophilic xenobiotic molecules as well as compounds of endogenous origin. Anthocyanin pigments require GSTs for their transport into the vacuole since their cytoplasmic retention is toxic to the cell. Anthocyanin accumulation in Citrus sinensis (L.) Osbeck fruit flesh determines different phenotypes affecting the typical pigmentation of Sicilian blood oranges. In this paper we describe: i) the characterization of the GST gene family in C. sinensis through a systematic EST analysis; ii) the validation of the EST assembly by exploiting the genome sequences of C. sinensis and C. clementina and their genome annotations; iii) GST gene expression profiling in six tissues/organs and in two different sweet orange cultivars, Cadenera (common) and Moro (pigmented).
We identified 61 GST transcripts, described the full- or partial-length nature of the sequences and assigned to each sequence the GST class membership exploiting a comparative approach and the classification scheme proposed for plant species. A total of 23 full-length sequences were defined. Fifty-four of the 61 transcripts were successfully aligned to the C. sinensis and C. clementina genomes. Tissue specific expression profiling demonstrated that the expression of some GST transcripts was 'tissue-affected' and cultivar specific. A comparative analysis of C. sinensis GSTs with those from other plant species was also considered. Data from the current analysis are accessible at, with the aim to provide a reference resource for C. sinensis GSTs.
This study aimed at the characterization of the GST gene family in C. sinensis. Based on expression patterns from two different cultivars and on sequence-comparative analyses, we also highlighted that two sequences, a Phi class GST and a Mapeg class GST, could be involved in the conjugation of anthocyanin pigments and in their transport into the vacuole, specifically in fruit flesh of the pigmented cultivar.
PMCID: PMC3922800  PMID: 24490620
Sweet orange; GST; Expressed sequence tag; Gene family; Anthocyanin vacuolarization
15.  Lotus tenuis x L. corniculatus interspecific hybridization as a means to breed bloat-safe pastures and gain insight into the genetic control of proanthocyanidin biosynthesis in legumes 
BMC Plant Biology  2014;14:40.
Proanthocyanidins (PAs) are secondary metabolites that strongly affect plant quality traits. The concentration and the structure of these metabolites influence the palatability and nutritional value of forage legumes. Hence, modulating PAs in the leaves of forage legumes is of paramount relevance for forage breeders worldwide. The lack of genetic variation in the leaf PA trait within the most important forage species and the difficulties in engineering this pathway via the ectopic expression of regulatory genes, prompted us to pursue alternative strategies to enhance this trait in forage legumes of agronomic interest. The Lotus genus includes forage species which accumulate PAs in edible organs and can thus be used as potential donor parents in breeding programs.
We recovered a wild, diploid and PA-rich population of L. corniculatus and crossed with L. tenuis. The former grows in an alkaline-salty area in Spain while the latter is a diploid species, grown extensively in South American pastures, which does not accumulate PAs in the herbage. The resulting interspecific hybrids displayed several traits of outstanding agronomic relevance such as rhizome production, PA levels in edible tissues sufficient to prevent ruminal bloating (around 5 mg of PAs/g DW), biomass production similar to the cultivated parent and potential for adaptability to marginal lands. We show that PA levels correlate with expression levels of the R2R3MYB transcription factor TT2 and, in turn, with those of the key structural genes of the epicatechin and catechin biosynthetic pathways leading to PA biosynthesis.
The L. tenuis x L. corniculatus hybrids, reported herein, represent the first example of the introgression of the PA trait in forage legumes to levels known to provide nutritional and health benefits to ruminants. Apart from PAs, the hybrids have additional traits which may prove useful to breed forage legumes with increased persistence and adaptability to marginal conditions. Finally, our study suggests the hybrids and their progeny are an invaluable tool to gain a leap forward in our understanding of the genetic control of PA biosynthesis and tolerance to stresses in legumes.
PMCID: PMC3927264  PMID: 24490637
Interspecific hybridization; Lotus; Proanthocyanidins (PAs); TT2; Forage legumes; Nutritive value
16.  LeMYC2 acts as a negative regulator of blue light mediated photomorphogenic growth, and promotes the growth of adult tomato plants 
BMC Plant Biology  2014;14:38.
Arabidopsis ZBF1/MYC2bHLH transcription factor is a repressor of photomorphogenesis, and acts as a point of cross talk in light, abscisic acid (ABA) and jasmonic acid (JA) signaling pathways. MYC2 also functions as a positive regulator of lateral root development and flowering time under long day conditions. However, the function of MYC2 in growth and development remains unknown in crop plants.
Here, we report the functional analyses of LeMYC2 in tomato (Lycopersicon esculentum). The amino acid sequence of LeMYC2 showed extensive homology with Arabidopsis MYC2, containing the conserved bHLH domain. To study the function of LeMYC2 in tomato, overexpression and RNA interference (RNAi) LeMYC2 tomato transgenic plants were generated. Examination of seedling morphology, physiological responses and light regulated gene expression has revealed that LeMYC2 works as a negative regulator of blue light mediated photomorphogenesis. Furthermore, LeMYC2 specifically binds to the G-box of LeRBCS-3A promoter. Overexpression of LeMYC2 has led to increased root length with more number of lateral roots. The tomato plants overexpressing LeMYC2 have reduced internode distance with more branches, and display the opposite morphology to RNAi transgenic lines. Furthermore, this study shows that LeMYC2 promotes ABA and JA responsiveness.
Collectively, this study highlights that working in light, ABA and JA signaling pathways LeMYC2 works as an important regulator for growth and development in tomato plants.
PMCID: PMC3922655  PMID: 24483714
17.  GIGANTUS1 (GTS1), a member of Transducin/WD40 protein superfamily, controls seed germination, growth and biomass accumulation through ribosome-biogenesis protein interactions in Arabidopsis thaliana 
BMC Plant Biology  2014;14:37.
WD40 domains have been found in a plethora of eukaryotic proteins, acting as scaffolding molecules assisting proper activity of other proteins, and are involved in multi-cellular processes. They comprise several stretches of 44-60 amino acid residues often terminating with a WD di-peptide. They act as a site of protein-protein interactions or multi-interacting platforms, driving the assembly of protein complexes or as mediators of transient interplay among other proteins. In Arabidopsis, members of WD40 protein superfamily are known as key regulators of plant-specific events, biologically playing important roles in development and also during stress signaling.
Using reverse genetic and protein modeling approaches, we characterize GIGANTUS1 (GTS1), a new member of WD40 repeat protein in Arabidopsis thaliana and provide evidence of its role in controlling plant growth development. GTS1 is highly expressed during embryo development and negatively regulates seed germination, biomass yield and growth improvement in plants. Structural modeling analysis suggests that GTS1 folds into a β-propeller with seven pseudo symmetrically arranged blades around a central axis. Molecular docking analysis shows that GTS1 physically interacts with two ribosomal protein partners, a component of ribosome Nop16, and a ribosome-biogenesis factor L19e through β-propeller blade 4 to regulate cell growth development.
Our results indicate that GTS1 might function in plant developmental processes by regulating ribosomal structural features, activities and biogenesis in plant cells. Our results suggest that GIGANTUS1 might be a promising target to engineer transgenic plants with higher biomass and improved growth development for plant-based bioenergy production.
PMCID: PMC3914372  PMID: 24467952
Arabidopsis; Gigantus1; Gene expression; Homology modeling; Docking
18.  Involvement of plant endogenous ABA in Bacillus megaterium PGPR activity in tomato plants 
BMC Plant Biology  2014;14:36.
Plant growth-promoting rhizobacteria (PGPR) are naturally occurring soil bacteria which benefit plants by improving plant productivity and immunity. The mechanisms involved in these processes include the regulation of plant hormone levels such as ethylene and abscisic acid (ABA). The aim of the present study was to determine whether the activity of Bacillus megaterium PGPR is affected by the endogenous ABA content of the host plant. The ABA-deficient tomato mutants flacca and sitiens and their near-isogenic wild-type parental lines were used. Growth, stomatal conductance, shoot hormone concentration, competition assay for colonization of tomato root tips, and root expression of plant genes expected to be modulated by ABA and PGPR were examined.
Contrary to the wild-type plants in which PGPR stimulated growth rates, PGPR caused growth inhibition in ABA-deficient mutant plants. PGPR also triggered an over accumulation of ethylene in ABA-deficient plants which correlated with a higher expression of the pathogenesis-related gene Sl-PR1b.
Positive correlation between over-accumulation of ethylene and a higher expression of Sl-PR1b in ABA-deficient mutant plants could indicate that maintenance of normal plant endogenous ABA content may be essential for the growth promoting action of B. megaterium by keeping low levels of ethylene production.
PMCID: PMC3903769  PMID: 24460926
Abscisic acid; Bacillus megaterium; Ethylene; Hormones; PGPR; Solanum lycopersicum; Rhizobacteria
19.  A Sorghum bicolor expression atlas reveals dynamic genotype-specific expression profiles for vegetative tissues of grain, sweet and bioenergy sorghums 
BMC Plant Biology  2014;14:35.
Effective improvement in sorghum crop development necessitates a genomics-based approach to identify functional genes and QTLs. Sequenced in 2009, a comprehensive annotation of the sorghum genome and the development of functional genomics resources is key to enable the discovery and deployment of regulatory and metabolic genes and gene networks for crop improvement.
This study utilizes the first commercially available whole-transcriptome sorghum microarray (Sorgh-WTa520972F) to identify tissue and genotype-specific expression patterns for all identified Sorghum bicolor exons and UTRs. The genechip contains 1,026,373 probes covering 149,182 exons (27,577 genes) across the Sorghum bicolor nuclear, chloroplast, and mitochondrial genomes. Specific probesets were also included for putative non-coding RNAs that may play a role in gene regulation (e.g., microRNAs), and confirmed functional small RNAs in related species (maize and sugarcane) were also included in our array design. We generated expression data for 78 samples with a combination of four different tissue types (shoot, root, leaf and stem), two dissected stem tissues (pith and rind) and six diverse genotypes, which included 6 public sorghum lines (R159, Atlas, Fremont, PI152611, AR2400 and PI455230) representing grain, sweet, forage, and high biomass ideotypes.
Here we present a summary of the microarray dataset, including analysis of tissue-specific gene expression profiles and associated expression profiles of relevant metabolic pathways. With an aim to enable identification and functional characterization of genes in sorghum, this expression atlas presents a new and valuable resource to the research community.
PMCID: PMC3925131  PMID: 24456189
Sorghum bicolor; Gene atlas; Transcriptome; Gene expression; Functional genomics; Microarray
20.  Exploring mechanisms linked to differentiation and function of dimorphic chloroplasts in the single cell C4 species Bienertia sinuspersici 
BMC Plant Biology  2014;14:34.
In the model single-cell C4 plant Bienertia sinuspersici, chloroplast- and nuclear-encoded photosynthetic enzymes, characteristically confined to either bundle sheath or mesophyll cells in Kranz-type C4 leaves, all occur together within individual leaf chlorenchyma cells. Intracellular separation of dimorphic chloroplasts and key enzymes within central and peripheral compartments allow for C4 carbon fixation analogous to NAD-malic enzyme (NAD-ME) Kranz type species. Several methods were used to investigate dimorphic chloroplast differentiation in B. sinuspersici.
Confocal analysis revealed that Rubisco-containing chloroplasts in the central compartment chloroplasts (CCC) contained more photosystem II proteins than the peripheral compartment chloroplasts (PCC) which contain pyruvate,Pi dikinase (PPDK), a pattern analogous to the cell type-specific chloroplasts of many Kranz type NAD-ME species. Transient expression analysis using GFP fusion constructs containing various lengths of a B. sinuspersici Rubisco small subunit (RbcS) gene and the transit peptide of PPDK revealed that their import was not specific to either chloroplast type. Immunolocalization showed the rbcL-specific mRNA binding protein RLSB to be selectively localized to the CCC in B. sinuspersici, and to Rubisco-containing BS chloroplasts in the closely related Kranz species Suaeda taxifolia. Comparative fluorescence analyses were made using redox-sensitive and insensitive GFP forms, as well comparative staining using the peroxidase indicator 3,3-diaminobenzidine (DAB), which demonstrated differences in stromal redox potential, with the CCC having a more negative potential than the PCC.
Both CCC RLSB localization and the differential chloroplast redox state are suggested to have a role in post-transcriptional rbcL expression.
PMCID: PMC3904190  PMID: 24443986
Single-cell C4 photosynthesis; Bienertia sinuspersici; Dimorphic chloroplasts; Chloroplast differentiation
21.  An integrated genetic map based on four mapping populations and quantitative trait loci associated with economically important traits in watermelon (Citrullus lanatus) 
BMC Plant Biology  2014;14:33.
Modern watermelon (Citrullus lanatus L.) cultivars share a narrow genetic base due to many years of selection for desirable horticultural qualities. Wild subspecies within C. lanatus are important potential sources of novel alleles for watermelon breeding, but successful trait introgression into elite cultivars has had limited success. The application of marker assisted selection (MAS) in watermelon is yet to be realized, mainly due to the past lack of high quality genetic maps. Recently, a number of useful maps have become available, however these maps have few common markers, and were constructed using different marker sets, thus, making integration and comparative analysis among maps difficult. The objective of this research was to use single-nucleotide polymorphism (SNP) anchor markers to construct an integrated genetic map for C. lanatus.
Under the framework of the high density genetic map, an integrated genetic map was constructed by merging data from four independent mapping experiments using a genetically diverse array of parental lines, which included three subspecies of watermelon. The 698 simple sequence repeat (SSR), 219 insertion-deletion (InDel), 36 structure variation (SV) and 386 SNP markers from the four maps were used to construct an integrated map. This integrated map contained 1339 markers, spanning 798 cM with an average marker interval of 0.6 cM. Fifty-eight previously reported quantitative trait loci (QTL) for 12 traits in these populations were also integrated into the map. In addition, new QTL identified for brix, fructose, glucose and sucrose were added. Some QTL associated with economically important traits detected in different genetic backgrounds mapped to similar genomic regions of the integrated map, suggesting that such QTL are responsible for the phenotypic variability observed in a broad array of watermelon germplasm.
The integrated map described herein enhances the utility of genomic tools over previous watermelon genetic maps. A large proportion of the markers in the integrated map are SSRs, InDels and SNPs, which are easily transferable across laboratories. Moreover, the populations used to construct the integrated map include all three watermelon subspecies, making this integrated map useful for the selection of breeding traits, identification of QTL, MAS, analysis of germplasm and commercial hybrid seed detection.
PMCID: PMC3898567  PMID: 24443961
Watermelon; Integrated genetic map; QTL; Sugar content
22.  Annual acknowledgement of manuscript reviewers 
BMC Plant Biology  2014;14:30.
Contributing reviewers
The editors of BMC Plant Biology would like to thank all of our reviewers who have contributed to the journal in Volume 13 (2013).
PMCID: PMC3897928
23.  Down-regulation of acetolactate synthase compromises Ol-1- mediated resistance to powdery mildew in tomato 
BMC Plant Biology  2014;14:32.
In a cDNA-AFLP analysis comparing transcript levels between powdery mildew (Oidium neolycopersici)-susceptible tomato cultivar Moneymaker (MM) and near isogenic lines (NILs) carrying resistance gene Ol-1 or Ol-4, a transcript-derived fragment (TDF) M11E69-195 was found to be present in NIL-Ol-1 but absent in MM and NIL-Ol-4. This TDF shows homology to acetolactate synthase (ALS). ALS is a key enzyme in the biosynthesis of branched-chain amino acids valine, leucine and isoleucine, and it is also a target of commercial herbicides.
Three ALS homologs ALS1, ALS2, ALS3 were identified in the tomato genome sequence. ALS1 and ALS2 show high similarity, whereas ALS3 is more divergent. Transient silencing of both ALS1 and ALS2 in NIL-Ol-1 by virus-induced gene silencing (VIGS) resulted in chlorotic leaf areas that showed increased susceptibility to O. neolycopersici (On). VIGS results were confirmed by stable transformation of NIL-Ol-1 using an RNAi construct targeting both ALS1 and ALS2. In contrast, silencing of the three ALS genes individually by RNAi constructs did not compromise the resistance of NIL-Ol-1. Application of the herbicide chlorsulfuron to NIL-Ol-1 mimicked the VIGS phenotype and caused loss of its resistance to On. Susceptible MM and On-resistant line NIL-Ol-4 carrying a nucleotide binding site and leucine rich repeat (NB-LRR) resistance gene were also treated with chlorsulfuron. Neither the susceptibility of MM nor the resistance of NIL-Ol-4 was affected.
ALS is neither involved in basal defense, nor in resistance conferred by NB-LRR type resistance genes. Instead, it is specifically involved in Ol-1-mediated resistance to tomato powdery mildew, suggesting that ALS-induced change in amino acid homeostasis is important for resistance conferred by Ol-1.
PMCID: PMC3898995  PMID: 24438198
Acetolactate synthase; Oidium neolycopersici; Resistance; Solanum lycoperisum; Amino acid homeostasis
24.  Genetic architecture of spring and autumn phenology in Salix 
BMC Plant Biology  2014;14:31.
In woody plants from temperate regions, adaptation to the local climate results in annual cycles of growth and dormancy, and optimal regulation of these cycles are critical for growth, long-term survival, and competitive success. In this study we have investigated the genetic background to growth phenology in a Salix pedigree by assessing genetic and phenotypic variation in growth cessation, leaf senescence and bud burst in different years and environments. A previously constructed linkage map using the same pedigree and anchored to the annotated genome of P. trichocarpa was improved in target regions and used for QTL analysis of the traits. The major aims in this study were to map QTLs for phenology traits in Salix, and to identify candidate genes in QTL hot spots through comparative mapping with the closely related Populus trichocarpa.
All traits varied significantly among genotypes and the broad-sense heritabilities ranged between 0.5 and 0.9, with the highest for leaf senescence. In total across experiment and years, 80 QTLs were detected. For individual traits, the QTLs explained together from 21.5 to 56.5% of the variation. Generally each individual QTL explained a low amount of the variation but three QTLs explained above 15% of the variation with one QTL for leaf senescence explaining 34% of the variation. The majority of the QTLs were recurrently identified across traits, years and environments. Two hotspots were identified on linkage group (LG) II and X where narrow QTLs for all traits co-localized.
This study provides the most detailed analysis of QTL detection for phenology in Salix conducted so far. Several hotspot regions were found where QTLs for different traits and QTLs for the same trait but identified during different years co-localised. Many QTLs co-localised with QTLs found in poplar for similar traits that could indicate common pathways for these traits in Salicaceae. This study is an important first step in identifying QTLs and candidate genes for phenology traits in Salix.
PMCID: PMC3945485  PMID: 24438179
Phenology; Adaptation; Salix; QTL; Candidate genes
25.  Ectoparasitic growth of Magnaporthe on barley triggers expression of the putative barley wax biosynthesis gene CYP96B22 which is involved in penetration resistance 
BMC Plant Biology  2014;14:26.
Head blast caused by the fungal plant pathogen Magnaporthe oryzae is an upcoming threat for wheat and barley cultivation. We investigated the nonhost response of barley to an isolate of the Magnaporthe species complex which is pathogenic on Pennisetum spp. as a potential source for novel resistance traits.
Array experiments identified a barley gene encoding a putative cytochrome P450 monooxygenase whose transcripts accumulate to a higher concentration in the nonhost as compared to the host interaction. The gene clusters within the CYP96 clade of the P450 plant gene family and is designated as CYP96B22. Expression of CYP96B22 was triggered during the ectoparasitic growth of the pathogen on the outside of the leaf. Usage of a fungicidal treatment and a Magnaporthe mutant confirmed that penetration was not necessary for this early activation of CYP96B22. Transcriptional silencing of CYP96B22 using Barley stripe mosaic virus led to a decrease in penetration resistance of barley plants to Magnaporthe host and nonhost isolates. This phenotype seems to be specific for the barley-Magnaporthe interaction, since penetration of the adapted barley powdery mildew fungus was not altered in similarly treated plants.
Taken together our results suggest a cross-talk between barley and Magnaporthe isolates across the plant surface. Since members of the plant CYP96 family are known to be involved in synthesis of epicuticular waxes, these substances or their derivatives might act as signal components. We propose a functional overlap of CYP96B22 in the execution of penetration resistance during basal and nonhost resistance of barley against different Magnaporthe species.
PMCID: PMC3897914  PMID: 24423145
Nonhost resistance; Magnaporthe oryzae; Head blast; Cytochrome P450; Wax; Cuticle; Penetration; BSMV-VIGS

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