The Roc10, a Rice Homeodomain-leucine Zipper Transcription Factor, Modulates Lignin Biosynthesis that Confers Drought Tolerance [RNA-seq]

Drought is a major environmental constraint affecting physiological, biochemical and molecular changes of crops, causing loss in crop productivities. Understanding the molecular mechanisms of drought tolerance is important for crop biotechnology. Here, we report that the rice (Oryza sativa) homeodomain-leucine zipper class IV transcription factor gene, Rice outermost cell-specific gene 10 (Roc10), improves drought tolerance and grain yield by increasing lignin accumulation in ground tissues of rice plants. Overexpression of Roc10 significantly enhanced drought tolerance of transgenic rice plants at the vegetative stages of growth with highly effective photosystem and reduction of water loss rate as compared with non-transgenic control and RNAi plants. More importantly, Roc10 overexpression plants had higher drought tolerance at the reproductive stage of growth with higher grain yield over controls under field-drought conditions. We identified downstream and putative target genes of Roc10 by using RNA-seq and ChIP-seq data of rice shoots. Roc10 overexpression elevated the expression levels of lignin biosynthetic genes in shoots with a concomitant increase in accumulation of lignin. The overexpression and RNAi lines showed opposite patterns of lignin accumulation. The Roc10 is mainly expressed in the outer cell layers including epidermis and vasculature of shoots that coincides with areas of increased lignification. Furthermore, the Roc10 was found to directly bind to the promoter of PEROXIDASEN/PEROXIDASE38, a key gene in lignin biosynthesis. Together, our findings suggested that the Roc10 confers drought stress tolerance by enhancing lignin biosynthesis in ground tissues of rice plants. Overall design: RNA-seq using leaves of NT and Roc10 transgenic plants.

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