Project description:Plant responses to drought stress require the regulation of transcriptional networks via drought responsive transcription factors, which mediate a range of morphological and physiological changes. AP2/ERF transcription factors are known to act as key regulators of drought resistance transcriptional networks; however, little is known about the associated molecular mechanisms that give rise to specific morphological and physiological adaptations. In this study, we functionally characterized the rice (Oryza sativa) drought responsive AP2/ERF transcription factor, OsERF71, which is predominantly expressed in the root meristem, pericycle, and endodermis. Overexpression of OsERF71 either throughout the entire plant or specifically in roots, resulted in a drought resistance phenotype at the vegetative growth stage, indicating that overexpression in roots was sufficient to confer drought resistance. The root specific overexpression was more effective in conferring drought resistance at the reproductive stage, such that grain yield was increased by 23-42% over wild type plants or whole-body overexpressing transgenic lines under drought conditions. OsERF71 overexpression in roots elevated the expression levels of genes related to cell wall loosening and lignin biosynthetic genes, which correlated with changes in root structure, the formation of enlarged aerenchyma and high lignification levels. Furthermore, OsERF71 was found to directly bind to the promoter of OsCCR1, a key gene in lignin biosynthesis. These results indicate that the OsERF71-mediated drought resistance pathway recruits factors involved in cell wall modification to enable root morphological adaptations, thereby providing a mechanism for enhancing drought resistance.
Project description:Freshwater is a limited and dwindling global resource; therefore, efficient water use is required for food crops that have high water demands, such as rice, or for the production of sustainable energy biomass. We show here that expression of the Arabidopsis HARDY (HRD) gene in rice improves water use efficiency, the ratio of biomass produced to the water used, by enhancing photosynthetic assimilation and reducing transpiration. These drought tolerant low-water-consuming rice plants exhibit increased shoot biomass under well irrigated conditions and an adaptive increase in root biomass under drought stress. The HRD gene, an AP2/ERF-like transcription factor, identified by a gain-of-function Arabidopsis mutant hrd-D having roots with enhanced strength, branching, and cortical cells, exhibits drought resistance and salt tolerance, accompanied by an enhancement in the expression of abiotic stress associated genes. Although HRD overexpression in Arabidopsis produces thicker leaves with more chloroplast-bearing mesophyll cells, in rice there is an increase in leaf biomass and bundle sheath cells that probably contribute to the enhanced photosynthesis assimilation and efficiency. HRD overexpression was also studied for clues of molecular mechanisms involved using microarrays. The results exemplify application of a gene identified from the model plant Arabidopsis for the improvement of water use efficiency coincident with drought resistance in the crop plant rice. Keywords: Genetic modification transcription factor overexpression mutant
Project description:The AP2/ERF family is one of the plant-specific transcription factors (TFs) whose members have been associated with various developmental processes and stress tolerance. Here, we functionally characterized the drought-inducible OsERF48, a group Ib member of the rice ERF family that contains four conserved motifs, CMI-1, 2, 3 and 4. Transactivation assay in yeast revealed that the CMI-1 at the C-terminal end was essential for its transcriptional activity. When the OsERF48 was overexpressed in an either root-specific (ROXOsERF48) or whole-body (OXOsERF48) expression manner, both transgenic plants showed a longer and denser root phenotype than the nontransgenic (NT) controls. When plants were grown on a 40% PEG-infused medium, an in vitro drought condition, ROXOsERF48 plants showed a more vigorous root growth over OXOsERF48 and NT plants. In addition, the ROXOsERF48 plants exhibited higher grain yield under field-drought conditions than OXOsERF48 and NT plants. We constructed a putative regulatory network of OsERF48 by cross-referencing of RNA-seq data of ROXOsERF48 roots with a co-expression network database, revealing an involvement of 20 drought-related genes. These include genes for stress signaling, carbohydrate metabolism, cell-wall proteins, and drought-response. More importantly, OsCML16, a key gene for calcium signaling during abiotic stress, was identified to be the direct target of OsERF48 by the ChIP-qPCR and the protoplast transient assay. Thus, our results demonstrated that OsERF48 regulates OsCML16, a calmodulin-like protein gene that enhance root growth and drought tolerance.
Project description:Drought is one of the most detrimental environmental factors that adversely affect crop production, thus jeopardizing food supplies for a growing world population. Over the past years, it has become evident that microorganisms associated with plants can enhance drought tolerance. However, the specific genetic and molecular mechanisms underpinning bacterial induction of drought tolerance in plants are still largely unknown.In our work, we have shown that a root endophytic Flavobacterium confers significant drought tolerance to Arabidopsis thaliana. We showed that the bacterium enhances drought tolerance by maintaining (and inducing) root hair formation and elongation under drought. By combining molecular, genetics, and omics technologies we identified an essential role of ethylene and two ethylene-induced transcription factors belonging to the ERF family (ERF115 and ERF114) through which flavobacterium exerts its effect on plant root hair formation and drought tolerance. Here we performed transcriptome analysis using RNA-seq to identify genes downstream of the two ERF transcription factors.
Project description:OsNAC6 is a stress responsive NAC transcription factor in rice known as a regulator for the transcriptional networks of the drought tolerance mechanisms. However, little is known about the associated molecular mechanisms for drought tolerance. Here, we identified OsNAC6-mediated root structural adaptation such as increased root number and root diameter that was sufficient to confer drought tolerance. Multiyear (5 years) drought field tests clearly demonstrated that OsNAC6 overexpression in roots produced higher grain yield under drought conditions. Genome-wide analyses revealed that OsNAC6 directly up-regulated 13 genes. Taken together, OsNAC6 is a valuable candidate for genetic engineering of drought-tolerant high-yielding crops.
Project description:OsNAC6 is a stress responsive NAC transcription factor in rice known as a regulator for the transcriptional networks of the drought tolerance mechanisms. However, little is known about the associated molecular mechanisms for drought tolerance. Here, we identified OsNAC6-mediated root structural adaptation such as increased root number and root diameter that was sufficient to confer drought tolerance. Multiyear (5 years) drought field tests clearly demonstrated that OsNAC6 overexpression in roots produced higher grain yield under drought conditions. Genome-wide analyses revealed that OsNAC6 directly up-regulated 13 genes. Taken together, OsNAC6 is a valuable candidate for genetic engineering of drought-tolerant high-yielding crops.
Project description:The functions of AP2/ERF family transcription factors in stress responses are well documented, but their roles in the brassinosteroid (BR)-regulated growth and stress responses have not been established. Here we show that stress-inducible AP2/ERF family transcription factor TINY inhibits BR-regulated growth while promoting drought response. TINY overexpression plants have stunted growth, increased sensitivity to BR biosynthesis inhibitors and compromised BR-responsive gene expression. In contrast, a tiny tiny2 tiny3 triple mutant has increased BR-regulated growth and BR-responsive gene expression. TINY positively regulates drought response by activating drought responsive genes and promoting abscisic acid-mediated stomatal closure. Global gene expression studies revealed that TINY and BRs oppositely regulate genes involved in plant growth and stress response. TINY interacts with and antagonizes BES1 in the regulation of these genes. The GSK3-like protein kinase BIN2, a negative regulator in the BR pathway, phosphorylates and stabilizes TINY, providing a mechanism for BR-mediated down-regulation of TINY to prevent activation of stress response under optimal growth conditions. Taken together, our results demonstrate that TINY is negatively regulated by BR signaling through BIN2 phosphorylation and positively regulates drought response, as well as inhibits BR-mediated plant growth through TINY-BES1 antagonistic interactions. Our results thus provide insight into the coordination of BR-regulated growth and drought responses.