Multifunctional Transcription Factor YABBY6 Regulates Morphogenesis, Drought and Cold Stress Responses in Rice.

The roles of plant-specific transcription factor family YABBY may vary among different members. OsYABBY6 is a rice YABBY gene, whose function is not well elucidated so far. In this paper, we show that OsYABBY6 is a nucleus-localized protein with transcriptional activation activity. OsYABBY6 is predominantly expressed in the palea and lemma, as well as in the sheath, culm and node. OsYABBY6 RNA interference (RNAi) plants exhibited altered plant height and larger grain size. Under cold treatment, OsYABBY6 overexpression (OE) plants had up-regulated expression of cold responsive genes, and accumulated less reactive oxygen species but more proline compared to wild type, resulting in improved cold tolerance. On the other hand, RNAi plants showed enhanced drought tolerance compared to the wild type by slower water loss, less reactive oxygen species but more proline and soluble sugar accumulation. In addition, endogenous abscisic acid (ABA) level was reduced in OsYABBY6 RNAi plants, and RNAi and OE plants were more and less sensitive to ABA treatment, respectively. Accordingly, we deduce that OsYABBY6 positively regulates cold response but negatively regulates drought response through different pathways. Our study reveals the crucial roles of OsYABBY6 in plant architecture and grain development, as well as in abiotic stress response, providing new insights into the functions of YABBYs in rice.