Plant microRNAs (miRNAs) play key roles in the transcriptional responses to environmental stresses. However, the role of miRNAs in responses to insect herbivory has not been thoroughly explored. To identify herbivory-responsive miRNAs, we identified conserved miRNAs in the ecological model plant Nicotiana attenuata whose interactions with herbivores have been well-characterized in both laboratory and field studies.
We identified 59 miRNAs from 36 families, and two endogenous trans-acting small interfering RNAs (tasiRNA) targeted by miRNAs. We characterized the response of the precursor and mature miRNAs to simulated attack from the specialist herbivore Manduca sexta by quantitative PCR analysis and used ir-aoc RNAi transformants, deficient in jasmonate biosynthesis, to identify jasmonate-dependent and -independent miRNA regulation. Expression analysis revealed that groups of miRNAs and tasiRNAs were specifically regulated by either mechanical wounding or wounding plus oral secretions from M. sexta larvae, and these small RNAs were accumulated in jasmonate-dependent or -independent manners. Moreover, cDNA microarray analysis indicated that the expression patterns of the corresponding target genes were correlated with the accumulation of miRNAs and tasiRNAs.
We show that a group of miRNAs and tasiRNAs orchestrates the expression of target genes involved in N. attenuata’s responses to herbivore attack.
Anti-herbivore defense; Jasmonate; Manduca sexta; miRNA; Nicotiana attenuata; tasiRNA
A plant’s endogenous clock (circadian clock) entrains physiological processes to light/dark and temperature cycles. Forward and reverse genetic approaches in Arabidopsis have revealed the mechanisms of the circadian clock and its components in the genome. Similar approaches have been used to characterize conserved clock elements in several plant species. A wild tobacco, Nicotiana attenuata has been studied extensively to understand responses to biotic or abiotic stress in the glasshouse and also in their native habitat. During two decades of field experiment, we observed several diurnal rhythmic traits of N. attenuata in nature. To expand our knowledge of circadian clock function into the entrainment of traits important for ecological processes, we here report three core clock components in N. attenuata.
Protein similarity and transcript accumulation allowed us to isolate orthologous genes of the core circadian clock components, LATE ELONGATED HYPOCOTYL (LHY), TIMING OF CAB EXPRESSION 1/PSEUDO-RESPONSE REGULATOR 1 (TOC1/PRR1), and ZEITLUPE (ZTL). Transcript accumulation of NaLHY peaked at dawn and NaTOC1 peaked at dusk in plants grown under long day conditions. Ectopic expression of NaLHY and NaZTL in Arabidopsis resulted in elongated hypocotyl and late-flowering phenotypes. Protein interactions between NaTOC1 and NaZTL were confirmed by yeast two-hybrid assays. Finally, when NaTOC1 was silenced in N. attenuata, late-flowering phenotypes under long day conditions were clearly observed.
We identified three core circadian clock genes in N. attenuata and demonstrated the functional and biochemical conservation of NaLHY, NaTOC1, and NaZTL.
Circadian clock; Flowering time; NaLHY; NaTOC1; NaZTL; Nicotiana attenuata; Protein interaction
To adjust their development to the environment, plants rely on specific signals that travel from shoot to root and vice versa. Here we describe an efficient micrografting protocol for Nicotiana attenuata, a useful tool for identifying these signals and understanding their functions. Additionally we analyzed transcript accumulation profiles of scions and rootstocks of grafts performed with wild-type and stably transformed N. attenuata. Our results are consistent with the source-to-sink movement of an sRNA silencing signal.
Grafting; Nicotiana attenuata; root and shoot signaling; systemic signals
Ecological performance is all about timing and the endogenous clock that allows the entrainment of rhythms and anticipation of fitness-determining events is being rapidly characterized. How plants anticipate daily abiotic stresses, such as cold in early mornings and drought at noon, as well as biotic stresses, such as the timing of pathogen infections, is being explored, but little is known about the clock's role in regulating responses to insect herbivores and mutualists, whose behaviors are known to be strongly diurnally regulated and whose attack is known to reconfigure plant metabolomes. We developed a liquid chromatography-mass spectrometry procedure and analyzed its output with model-based peak picking algorithms to identify metabolites with diurnal accumulation patterns in sink/source leaves and roots in an unbiased manner. The response of metabolites with strong diurnal patterns to simulated attack from the specialist herbivore, Manduca sexta larvae was analyzed and annotated with in-house and public databases. Roots and leaves had largely different rhythms and only 10 ions of 182 oscillating ions in leaves and 179 oscillating ions in roots were rhythmic in both tissues: root metabolites mainly peaked at dusk or night, while leaf metabolites peaked during the day. Many oscillating metabolites showed tissue-specific regulation by simulated herbivory of which systemic responses in unattacked tissues were particularly pronounced. Diurnal and herbivory-elicited accumulation patterns of disaccharide, phenylalanine, tyrosine, lyciumoside I, coumaroyl tyramine, 12-oxophytodienoic acid and jasmonic acid and those of their related biosynthetic transcripts were examined in detail. We conclude that oscillating metabolites of N. attenuata accumulate in a highly tissue-specific manner and the patterns reveal pronounced diurnal rhythms in the generalized and specialized metabolism that mediates the plant's responses to herbivores and mutualists. We propose that diurnal regulation will prove to an important element in orchestrating a plant's responses to herbivore attack.
Head blight, caused by Gibberella zeae, is a significant disease among cereal crops, including wheat, barley, and rice, due to contamination of grain with mycotoxins. G. zeae is spread by ascospores forcibly discharged from sexual fruiting bodies forming on crop residues. In this study, we characterized a novel gene, ROA, which is required for normal sexual development. Deletion of ROA (Δroa) resulted in an abnormal size and shape of asci and ascospores but did not affect vegetative growth. The Δroa mutation triggered round ascospores and insufficient cell division after spore delimitation. The asci of the Δroa strain discharged fewer ascospores from the perithecia but achieved a greater dispersal distance than those of the wild-type strain. Turgor pressure within the asci was calculated through the analysis of osmolytes in the epiplasmic fluid. Deletion of the ROA gene appeared to increase turgor pressure in the mutant asci. The higher turgor pressure of the Δroa mutant asci and the mutant spore shape contributed to the longer distance dispersal. When the Δroa mutant was outcrossed with a Δmat1-2 mutant, a strain that contains a green fluorescence protein (GFP) marker in place of the MAT1-2 gene, unusual phenotypic segregation occurred. The ratio of GFP to non-GFP segregation was 1:1; however, all eight spores had the same shape. Taken together, the results of this study suggest that ROA plays multiple roles in maintaining the proper morphology and discharge of ascospores in G. zeae.
Anaphylaxis or anaphylactoid reaction in pediatric patient during anesthesia is rare. We report a rocuronium induced anaphylactic reaction in a 33-month-old female. The patient was scheduled to undergo escharectomy due to injuries suffered from a major burn. Shortly after administration of rocuronium, the patient developed severe hypotension, tachycardia, and hypoxia. A similar reaction occurred after administration of rocuronium on subsequent anesthesia. She underwent uneventful anesthesia with volatile induction and maintenance of anesthesia with sevoflurane on her next 7 operations without using of muscle relaxant.
Anaphylactoid reaction; Anaphylaxis; Muscle relaxant; Pediatrics; Rocuronium
Competitive inhibition of transcription factors by small proteins is an intriguing component of gene regulatory networks in both animals and plants. The small interfering proteins possess limited sequence homologies to specific transcription factors but lack one or more protein motifs required for transcription factor activities. They interfere with the activities of transcription factors, such as DNA binding and transcriptional activation, by forming nonfunctional heterodimers. A potential example is the Arabidopsis MIF1 (mini zinc finger 1) protein consisting of 101 residues. It has a zinc finger domain but lacks other protein motifs normally present in transcription factors. In this work, we show that MIF1 and its functional homologues physically interact with a group of zinc finger homeodomain (ZHD) transcription factors, such as ZHD5, that regulate floral architecture and leaf development. Gel mobility shift assays revealed that MIF1 blocks the DNA binding activity of ZHD5 homodimers by competitively forming MIF1-ZHD5 heterodimers. Accordingly, the transcriptional activation activity of ZHD5 was significantly suppressed by MIF1 coexpressed transiently in Arabidopsis protoplasts. Notably, MIF1 also prevents ZHD5 from nuclear localization. Although ZHD5 was localized exclusively in the nucleus, it was scattered throughout the cytoplasm when MIF1 was coexpressed. Transgenic plants overexpressing the ZHD5 gene (35S:ZHD5) exhibited accelerated growth with larger leaves. Consistent with the negative regulation of ZHD5 by MIF1, the 35S:ZHD5 phenotypes were diminished by MIF1 coexpression. These observations indicate that MIF1 regulates the ZHD5 activities in a dual step manner: nuclear import and DNA binding.
Arabidopsis; DNA-binding Protein; Gene Expression; Plant; Transcription Factors; Zinc Finger
Seed germination initiates the postembryonic development of plants, which determines successful seedling establishment and plant propagation. It is therefore tightly regulated by diverse environmental conditions, including high salinity and drought, as well as by intrinsic developmental programs, among which gibberellic acid (GA) is best understood. Regulatory roles of GA in seed germination have been extensively studied. It is also known that high salinity inhibits germination by repressing genes encoding GA biosynthetic enzymes. However, it is still unclear how salt signals are coordinately incorporated into the GA signaling pathway at the molecular level. We recently demonstrated that a membrane-bound NAC transcription factor, NTL8, mediates salt signaling, primarily through a RGL2-independent GA pathway, in regulating seed germination. High salinity promotes NTL8 transcription and proteolytic activation of NTL8. Notably, the NTL8-mediated salt signaling is independent of abscisic acid (ABA). These observations indicate that membrane-mediated transcription control is an important component of salt signaling during seed germination.
Arabidopsis; gibberellic acid (GA); salt stress; membrane-bound transcription factor; NAC; NTL8; RGL2
Transcription factors are key components of transcriptional regulatory networks governing virtually all aspects of plant growth and developmental processes. Their activities are regulated at various steps, including gene transcription, posttranscriptional mRNA metabolism, posttranslational modifications, nucleocytoplasmic transport, and controlled proteolytic cleavage of membrane-anchored, dormant forms. Dynamic protein dimerization also plays a critical role in this process. An exquisite regulatory scheme has recently been proposed to modulate the action of transcription factors. Small peptides possessing a protein dimerization motif but lacking the DNA-binding motif form nonfunctional heterodimers with a group of specific TFs, inhibiting their transcriptional activation activities. Extensive searches for small proteins that have a similar structural organization in the databases revealed that small peptide-mediated transcription control is not an exceptional case but would be a regulatory mechanism occurring widespread in the Arabidopsis genome.
Arabidopsis; flowering time; HD-ZIP III; homodimer; transcription factor; ZPR
More than 10% of the plant-specific NAC (NAM, ATAF1/2, CUC2) transcription factors have been predicted to have alpha-helical transmembrane (TM) domain in their C-terminal regions, among which at least three members have been proven to be membrane-associated and play a role in cell cycle control and stress responses. These observations suggest that membrane-mediated regulation would be an important molecular mechanism mediating rapid transcriptional responses to internal and external stimuli in plants. Recently, we showed that a salt-responsive NTL (NTM1-Like's) transcription factor NTL8 is localized primarily in plasma membranes as dormant form and subsequently processed into transcriptionally active, nuclear form. Overexpression of an active NTL8 form exhibited delayed flowering as well as reduced growth with small curled leaves. Consistent with this, expression of FLOWERING LOCUS T (FT) and its downstream genes was significantly reduced in the transgenic plants. Furthermore, FT was notably repressed by high salt. These results indicate that NTL8 mediates salt-responsive flowering via FT in Arabidopsis and that membrane-mediated transcription regulation underlies the salt signaling in mediating flowering initiation.
Arabidopsis; flowering time; flowering locus T (FT); membrane-bound transcription factor; NAC; salt stress
Controlled proteolytic cleavage of membrane-associated transcription factors (MTFs) is an intriguing activation strategy that ensures rapid transcriptional responses to incoming stimuli. Several MTFs are known to regulate diverse cellular functions in prokaryotes, yeast, and animals. In Arabidopsis, a few NAC MTFs mediate either cytokinin signaling during cell division or endoplasmic reticulum (ER) stress responses. Through genome-wide analysis, it was found that at least 13 members of the NAC family in Arabidopsis contain strong α-helical transmembrane motifs (TMs) in their C-terminal regions and are predicted to be membrane-associated. Interestingly, most of the putative NAC MTF genes are up-regulated by stress conditions, suggesting that they may be involved in stress responses. Notably, transgenic studies revealed that membrane release is essential for the function of NAC MTFs. Transgenic plants overexpressing partial-size NAC constructs devoid of the TMs, but not those overexpressing full-size constructs, showed distinct phenotypic changes, including dwarfed growth and delayed flowering. The rice genome also contains more than six NAC MTFs. Furthermore, the presence of numerous MTFs is predicted in the whole transcription factors in plants. We thus propose that proteolytic activation of MTFs is a genome-wide mechanism regulating plant genomes.