Search

Soybean (Glycine max) is the most important dicot crop worldwide, and is increasingly used as a model legume due to the wide availability of genomic soybean resources; however, the slow generation times of soybean plants are currently a major hindrance to research. Here, we demonstrate a method for accelerating soybean breeding in compact growth chambers, which greatly shortens the generation time of the plants and accelerates breeding and research projects. Our breeding method utilizes commonly used fluorescent lamps (220 µmol m–2 s–1 at the canopy level), a 14 h light (30°C)/10 h dark (25°C) cycle and carbon dioxide (CO2) supplementation at >400 p.p.m. Using this approach, the generation time of the best-characterized elite Japanese soybean cultivar, Enrei, was shortened from 102–132 d reported in the field to just 70 d, thereby allowing up to 5 generations per year instead of the 1–2 generations currently possible in the field and/or greenhouse. The method also facilitates the highly efficient and controlled crossing of soybean plants. Our method uses CO2 supplementation to promote the growth and yield of plants, appropriate light and temperature conditions to reduce the days to flowering, and the reaping and sowing of immature seeds to shorten the reproductive period greatly. Thus, the appropriate parameters enable acceleration of soybean breeding in the compact growth chambers commonly used for laboratory research. The parameters used in our method could therefore be optimized for other species, cultivars, accessions and experimental designs to facilitate rapid breeding in a wide range of crops. [ABSTRACT FROM AUTHOR]

In plants, osmotic stress-responsive transcriptional regulation depends mainly on two major classes of cis-acting elements found in the promoter regions of stress-inducible genes: ABA-responsive elements (ABREs) and dehydration-responsive elements (DREs). ABRE has been shown to perceive ABA-mediated osmotic stress signals, whereas DRE is known to be involved in an ABA-independent pathway. Previously, we reported that the transcription factor DRE-BINDING PROTEIN 2A (DREB2A) regulates DRE-mediated transcription of target genes under osmotic stress conditions in Arabidopsis (Arabidopsis thaliana). However, the transcriptional regulation of DREB2A itself remains largely uncharacterized. To elucidate the transcriptional mechanism associated with the DREB2A gene under osmotic stress conditions, we generated a series of truncated and base-substituted variants of the DREB2A promoter and evaluated their transcriptional activities individually. We found that both ABRE and coupling element 3 (CE3)-like sequences located approximately −100 bp from the transcriptional initiation site are necessary for the dehydration-responsive expression of DREB2A. Coupling our transient expression analyses with yeast one-hybrid and chromatin immunoprecipitation (ChIP) assays indicated that the ABRE-BINDING PROTEIN 1 (AREB1), AREB2 and ABRE-BINDING FACTOR 3 (ABF3) bZIP transcription factors can bind to and activate the DREB2A promoter in an ABRE-dependent manner. Exogenous ABA application induced only a modest accumulation of the DREB2A transcript when compared with the osmotic stress treatment. However, the osmotic stress-induced DREB2A expression was found to be markedly impaired in several ABA-deficient and ABA-insensitive mutants. These results suggest that in addition to an ABA-independent pathway, the ABA-dependent pathway plays a positive role in the osmotic stress-responsive expression of DREB2A. [ABSTRACT FROM PUBLISHER]

The subclass III group of SNF1-related protein kinase 2 (SnRK2) members is known to play an important role in ABA and osmotic stress signaling in Arabidopsis; however, the roles of other subclasses remain elusive. Here, we established a double mutant of SRK2C/SnR2.8 and SRK2F/SnRK2.7 to investigate the functions of subclass II SnRK2s. Microarray analysis suggested that subclass II SnRK2s regulate some drought-responsive genes involving ABA-responsive element binding transcription factors (AREB/ABF) and their targets, and quantitative reverse transcription– PCR confirmed that those genes were down-regulated significantly in srk2cf. This study indicates that subclass II SnRK2s also play important roles in drought stress signaling in Arabidopsis. [ABSTRACT FROM PUBLISHER]

Responses to water stress are thought to be mediated by transcriptional regulation of gene expression via reversible protein phosphorylation events. Previously, we reported that bZIP (basic-domain leucine zipper)-type AREB/ABF (ABA-responsive element-binding protein/factor) transcription factors are involved in ABA signaling under water stress conditions in Arabidopsis. The AREB1 protein is phosphorylated in vitro by ABA-activated SNF1-related protein kinase 2s (SnRK2s) such as SRK2D/SnRK2.2, SRK2E/SnRK2.6 and SRK2I/SnRK2.3 (SRK2D/E/I). Consistent with this, we now show that SRK2D/E/I and AREB1 co-localize and interact in nuclei in planta. Our results show that unlike srk2d, srk2e and srk2i single and double mutants, srk2d srk2e srk2i (srk2d/e/i) triple mutants exhibit greatly reduced tolerance to drought stress and highly enhanced insensitivity to ABA. Under water stress conditions, ABA- and water stress-dependent gene expression, including that of transcription factors, is globally and drastically impaired, and jasmonic acid (JA)-responsive and flowering genes are up-regulated in srk2d/e/i triple mutants, but not in other single and double mutants. The down-regulated genes in srk2d/e/i and areb/abf triple mutants largely overlap in ABA-dependent expression, supporting the view that SRK2D/E/I regulate AREB/ABFs in ABA signaling in response to water stress. Almost all dehydration-responsive LEA (late embryogenesis abundant) protein genes and group-A PP2C (protein phosphatase 2C) genes are strongly down-regulated in the srk2d/e/i triple mutants. Further, our data show that these group-A PP2Cs, such as HAI1 and ABI1, interact with SRK2D. Together, our results indicate that SRK2D/E/I function as main positive regulators, and suggest that ABA signaling is controlled by the dual modulation of SRK2D/E/I and group-A PP2Cs. [ABSTRACT FROM PUBLISHER]

A 6-bp sequence, ACTCAT, acts as a cis-acting element involved in hypoosmolarity- and proline-responsive expression of an Arabidopsis proline dehydrogenase (ProDH) gene. Search of the database for plant cis-acting elements revealed that the ACTCAT sequence is similar to the GCN4 motif [ATGA(C/G)TCAT] that is recognized by bZIP transcription factors. To identify transcription factor(s) for regulation of ProDH, we examined whether Arabidopsis bZIPs function as transcription factors for the ACTCAT sequence. Transient expression analysis revealed that the four proteins in Group S bZIPs, AtbZIP11/ATB2, AtbZIP44, AtbZIP2/GBF5 and AtbZIP53, formed an ATB2 subgroup that activated expression of the GUS reporter gene driven by the ACTCAT sequence while other bZIPs and different families of plant transcription factors did not. The transactivation activity of the ATB2 subgroup was enhanced in a hypoosmotic condition. In a gel mobility shift assay, the recombinant proteins of the ATB2 subgroup specifically bound to the ACTCAT sequence. RNA gel blot analysis indicated that the expression of AtbZIP2/GBF5 and AtbZIP53, as well as that of ProDH, is induced by hypoosmolarity. Moreover, we showed that the sGFP::AtbZIP11/ATB2 fusion protein is localized in the nucleus. These results suggest that the ATB2 subgroup functions as a transcriptional activator for hypoosmolarity-inducible ProDH in Arabidopsis. [ABSTRACT FROM AUTHOR]