Search

Summary: Drought stress seriously impacts on plant development and productivity. Improvement of drought tolerance without yield penalty is a great challenge in crop biotechnology. Here, we report that the rice (Oryza sativa) homeodomain‐leucine zipper transcription factor gene, OsTF1L (Oryza sativa transcription factor 1‐like), is a key regulator of drought tolerance mechanisms. Overexpression of the OsTF1L in rice significantly increased drought tolerance at the vegetative stages of growth and promoted both effective photosynthesis and a reduction in the water loss rate under drought conditions. Importantly, the OsTF1L overexpressing plants showed a higher drought tolerance at the reproductive stage of growth with a higher grain yield than nontransgenic controls under field‐drought conditions. Genomewide analysis of OsTF1L overexpression plants revealed up‐regulation of drought‐inducible, stomatal movement and lignin biosynthetic genes. Overexpression of OsTF1L promoted accumulation of lignin in shoots, whereas the RNAi lines showed opposite patterns of lignin accumulation. OsTF1L is mainly expressed in outer cell layers including the epidermis, and the vasculature of the shoots, which coincides with areas of lignification. In addition, OsTF1L overexpression enhances stomatal closure under drought conditions resulted in drought tolerance. More importantly, OsTF1L directly bound to the promoters of lignin biosynthesis and drought‐related genes involving poxN/PRX38, Nodulin protein,DHHC4,CASPL5B1 and AAA‐type ATPase. Collectively, our results provide a new insight into the role of OsTF1L in enhancing drought tolerance through lignin biosynthesis and stomatal closure in rice. [ABSTRACT FROM AUTHOR]

The AP2/ ERF family is a plant-specific transcription factor family whose members have been associated with various developmental processes and stress tolerance. Here, we functionally characterized the drought-inducible Os ERF48, a group Ib member of the rice ERF family with four conserved motifs, CMI-1, -2, -3 and -4. A transactivation assay in yeast revealed that the C-terminal CMI-1 motif was essential for Os ERF48 transcriptional activity. When Os ERF48 was overexpressed in an either a root-specific ( ROX O s ERF 48) or whole-body ( OX O s ERF 48) manner, transgenic plants showed a longer and denser root phenotype compared to the nontransgenic ( NT) controls. When plants were grown on a 40% polyethylene glycol-infused medium under in vitro drought conditions, ROX O s ERF 48 plants showed a more vigorous root growth than OX O s ERF 48 and NT plants. In addition, the ROX O s ERF 48 plants exhibited higher grain yield than OX O s ERF 48 and NT plants under field-drought conditions. We constructed a putative Os ERF48 regulatory network by cross-referencing ROX O s ERF 48 root-specific RNA-seq data with a co-expression network database, from which we inferred the involvement of 20 drought-related genes in Os ERF48-mediated responses. These included genes annotated as being involved in stress signalling, carbohydrate metabolism, cell-wall proteins and drought responses. They included, Os CML16, a key gene in calcium signalling during abiotic stress, which was shown to be a direct target of Os ERF48 by chromatin immunoprecipitation- qPCR analysis and a transient protoplast expression assay. Our results demonstrated that Os ERF48 regulates Os CML16, a calmodulin-like protein gene that enhances root growth and drought tolerance. [ABSTRACT FROM AUTHOR]

Drought has a serious impact on agriculture worldwide. A plant's ability to adapt to rhizosphere drought stress requires reprogramming of root growth and development. Although physiological studies have documented the root adaption for tolerance to the drought stress, underlying molecular mechanisms is still incomplete, which is essential for crop engineering. Here, we identified Os NAC6-mediated root structural adaptations, including increased root number and root diameter, which enhanced drought tolerance. Multiyear drought field tests demonstrated that the grain yield of Os NAC6 root-specific overexpressing transgenic rice lines was less affected by drought stress than were nontransgenic controls. Genome-wide analyses of loss- and gain-of-function mutants revealed that Os NAC6 up-regulates the expression of direct target genes involved in membrane modification, nicotianamine ( NA) biosynthesis, glutathione relocation, 3′-phophoadenosine 5′-phosphosulphate accumulation and glycosylation, which represent multiple drought tolerance pathways. Moreover, overexpression of NICOTIANAMINE SYNTHASE genes, direct targets of Os NAC6, promoted the accumulation of the metal chelator NA and, consequently, drought tolerance. Collectively, Os NAC6 orchestrates novel molecular drought tolerance mechanisms and has potential for the biotechnological development of high-yielding crops under water-limiting conditions. [ABSTRACT FROM AUTHOR]

Protein-binding DNA microarray (PBM) is one of the high-throughput methods to define DNA sequences which potentially bind to a given DNA-binding protein. Quadruple 9-mer-based protein-binding DNA microarray, named Q9-PBM, is designed in such a way that target probes are synthesized as quadruples of all possible 9-mer combinations. Also, recombinant proteins fused with DsRed-monomer fluorescent protein are conveniently constructed. Q9-PBM confirms the well-known DNA-binding sequences of Cbf1 and CBF1/DREB1B transcription factors, and also identifies the adjacent sequences. Moreover, Q9-PBM is applied to elucidate the unidentified cis-acting element of the OsNAC6 rice transcription factor. This technology will facilitate greater understanding of genome-wide interactions between proteins and DNA.

Histone deacetylases (HDACs) modulate chromatin structure and transcription. Previously, we have shown that transgenic overexpression of OsHDAC1 gene alters the seedling root growth. In the current report, we have identified a group of genes that are transcriptionally repressed in the OsHDAC1 overexpressors (OsHDAC1(OE)) by performing a global profiling of root expressed genes. The OsNAC6 gene, a member of NAC family, was identified as a key component of the OsHDAC1 regulon and found to be repressed in OsHDAC1(OE). The root growth of OsNAC6 knock-out (OsNAC6(KO)) seedlings was observed to be similar to that of the OsHDAC1(OE) seedlings. Conversely, the root growth of the OsNAC6 overexpressors (OsNAC6(OE)) was similar to that of the OsHDAC1 knock-out (OsHDAC1(KO)) seedlings. We further demonstrated that OsHDAC1 interact with the OsNAC6 gene promoter at a epigenetic level by deacetylating K9, K14 and K18 on H3 and K5, K12 and K16 on H4. Overall, our results suggest that OsHDAC1 represses the OsNAC6 gene expression, which is primarily responsible for the alteration of root growth of rice seedlings.