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1.  Identification and expression analysis of the Glycine max CYP707A gene family in response to drought and salt stresses 
Annals of Botany  2012;110(3):743-756.
Background and Aims
Abscisic acid (ABA) plays crucial roles in plants' responses to abiotic stresses. ABA 8′-hydroxylation controlled by CYP707A genes has been well studied in Arabidopsis and rice, but not in legumes. The aims of the present study were to identify and functionally analyse the soybean CYP707A gene family, and to explore their expression patterns under dehydration and salt stresses.
Methods
A complementation experiment was employed to verify the function of soybean CYP707A1a in ABA catabolism. Genomic and cDNA sequences of other soybean CYP707A genes were isolated from the Phytozome database based on soybean CYP707A1a. The structure and phylogenetic relationship of this gene family was further analysed. The expression patterns of soybean CYP707A genes under dehydration and salt stress were analysed via quantitative real-time PCR.
Key Results
Over-expression of GmCYP707A1a in the atcyp707a2 T-DNA insertion mutant decreased its sensitivity to ABA, indicating that GmCYP707A1a indeed functions as an ABA 8′-hydroxylase in higher plants. The soybean genome contains ten CYP707A genes. Gene structure and phylogenetic analysis showed high conservation of ten GmCYP707A genes to the other CYP707A genes from monocots and dicots. Seed imbibition induced expression of A1a, A1b, A2a, A2b, A2c, A3a and A5 in embryo, and expression of A1a, A1b, A2a and A2b in cotyledon. Dehydration induced expression of A1a, A1b, A2b, A2c, A3a, A3b, A4a, A4b and A5 both in roots and in leaves, whereas rehydration stimulated transcription of A2a, A2b, A3b, A4a and A5 in roots, and only A3b and A5 in leaves. Expression of all soybean CYP707A genes was induced either by short- or by long-term salt stress.
Conclusions
The first biological evidence is provided that GmCYP7071a encodes an ABA 8′-hydroxylase through transgenic studies. Ten soybean GmCYP707A genes were identified, most of them expressed in multiple soybean tissues, and were induced by imbibition, dehydration and salinity.
doi:10.1093/aob/mcs133
PMCID: PMC3400457  PMID: 22751653
Abscisic acid; ABA catabolism; Glycine max; CYP707A gene family; drought; salt stress
2.  Identification of soybean purple acid phosphatase genes and their expression responses to phosphorus availability and symbiosis 
Annals of Botany  2011;109(1):275-285.
Background and Aims
Purple acid phosphatases (PAPs) are members of the metallo-phosphoesterase family and have been known to play important roles in phosphorus (P) acquisition and recycling in plants. Low P availability is a major constraint to growth and production of soybean, Glycine max. Comparative studies on structure, transcription regulation and responses to phosphate (Pi) deprivation of the soybean PAP gene family should facilitate further insights into the potential physiological roles of GmPAPs.
Methods
BLAST searches were performed to identify soybean PAP genes at the phytozome website. Bioinformatic analyses were carried out to investigate their gene structure, conserve motifs and phylogenetic relationships. Hydroponics and sand-culture experiments were carried out to obtain the plant materials. Quantitative real-time PCR was employed to analyse the expression patterns of PAP genes in response to P deficiency and symbiosis.
Key Results
In total, 35 PAP genes were identified from soybean genomes, which can be classified into three distinct groups including six subgroups in the phylogenetic tree. The expression pattern analysis showed flowers possessed the largest number of tissue-specific GmPAP genes under normal P conditions. The expression of 23 GmPAPs was induced or enhanced by Pi starvation in different tissues. Among them, nine GmPAP genes were highly expressed in the Pi-deprived nodules, whereas only two GmPAP genes showed significantly increased expression in the arbuscular mycorrhizal roots under low-P conditions.
Conclusions
Most GmPAP genes are probably involved in P acquisition and recycling in plants. Also we provide the first evidence that some members of the GmPAP gene family are possibly involved in the response of plants to symbiosis with rhizobia or arbuscular mycorrhizal fungi under P-limited conditions.
doi:10.1093/aob/mcr246
PMCID: PMC3241574  PMID: 21948626
Soybean; Glycine max; purple acid phosphatase; expression analysis; phylogenetic analysis; phosphorus nutrition; symbiosis
3.  Genetic improvement for phosphorus efficiency in soybean: a radical approach 
Annals of Botany  2010;106(1):215-222.
Background
Low phosphorus (P) availability is a major constraint to soybean growth and production. Developing P-efficient soybean varieties that can efficiently utilize native P and added P in the soils would be a sustainable and economical approach to soybean production.
Scope
This review summarizes the possible mechanisms for P efficiency and genetic strategies to improve P efficiency in soybean with examples from several case studies. It also highlights potential obstacles and depicts future perspectives in ‘root breeding’.
Conclusions
This review provides new insights into the mechanisms of P efficiency and breeding strategies for this trait in soybean. Root biology is a new frontier of plant biology. Substantial efforts are now focusing on increasing soybean P efficiency through ‘root breeding’. To advance this area, additional collaborations between plant breeders and physiologists, as well as applied and theoretical research are needed to develop more soybean varieties with enhanced P efficiency through root modification, which might contribute to reduced use of P fertilizers, expanding agriculture on low-P soils, and achieving more sustainable agriculture.
doi:10.1093/aob/mcq029
PMCID: PMC2889788  PMID: 20228090
Soybean; genetic improvement; phosphorus efficiency; root breeding
4.  QTL analysis of root traits as related to phosphorus efficiency in soybean 
Annals of Botany  2010;106(1):223-234.
Background and Aims
Low phosphorus (P) availability is a major constraint to soybean growth and production, especially in tropical and subtropical areas. Root traits have been shown to play critical roles in P efficiency in crops. Identification of the quantitative trait loci (QTLs) conferring superior root systems could significantly enhance genetic improvement in soybean P efficiency.
Methods
A population of 106 F9 recombinant inbred lines (RILs) derived from a cross between BD2 and BX10, which contrast in both P efficiency and root architecture, was used for mapping and QTL analysis. Twelve traits were examined in acid soils. A linkage map was constructed using 296 simple sequence repeat (SSR) markers with the Kosambi function, and the QTLs associated with these traits were detected by composite interval mapping and multiple-QTL mapping.
Key Results
The first soybean genetic map based on field data from parental genotypes contrasting both in P efficiency and root architecture was constructed. Thirty-one putative QTLs were detected on five linkage groups, with corresponding contribution ratios of 9·1–31·1 %. Thirteen putative QTLs were found for root traits, five for P content, five for biomass and five for yield traits. Three clusters of QTLs associated with the traits for root and P efficiency at low P were located on the B1 linkage group close to SSR markers Satt519 and Satt519-Sat_128, and on the D2 group close to Satt458; and one cluster was on the B1 linkage group close to Satt519 at high P.
Conclusions
Most root traits in soybean were conditioned by more than two minor QTLs. The region closer to Satt519 on the B1 linkage group might have great potential for future genetic improvement for soybean P efficiency through root selection.
doi:10.1093/aob/mcq097
PMCID: PMC2889805  PMID: 20472699
Quantitative trait loci (QTLs); soybean; Glycine max; root traits; phosphorus efficiency
5.  Aluminium tolerance and high phosphorus efficiency helps Stylosanthes better adapt to low-P acid soils 
Annals of Botany  2009;103(8):1239-1247.
Backgrond and Aims
Stylosanthes spp. (stylo) is one of the most important pasture legumes used in a wide range of agricultural systems on acid soils, where aluminium (Al) toxicity and phosphorus (P) deficiency are two major limiting factors for plant growth. However, physiological mechanisms of stylo adaptation to acid soils are not understood.
Methods
Twelve stylo genotypes were surveyed under field conditions, followed by sand and nutrient solution culture experiments to investigate possible physiological mechanisms of stylo adaptation to low-P acid soils.
Key Results
Stylo genotypes varied substantially in growth and P uptake in low P conditions in the field. Three genotypes contrasting in P efficiency were selected for experiments in nutrient solution and sand culture to examine their Al tolerance and ability to utilize different P sources, including Ca-P, K-P, Al-P, Fe-P and phytate-P. Among the three tested genotypes, the P-efficient genotype ‘TPRC2001-1’ had higher Al tolerance than the P-inefficient genotype ‘Fine-stem’ as indicated by relative tap root length and haematoxylin staining. The three genotypes differed in their ability to utilize different P sources. The P-efficient genotype, ‘TPRC2001-1’, had superior ability to utilize phytate-P.
Conclusions
The findings suggest that possible physiological mechanisms of stylo adaptation to low-P acid soils might involve superior ability of plant roots to tolerate Al toxicity and to utilize organic P and Al-P.
doi:10.1093/aob/mcp074
PMCID: PMC2685318  PMID: 19324896
Stylosanthes; phosphorus; P efficiency; organic P; Al toxicity; acid soil

Results 1-5 (5)