The OsRFP1-OsMYB61 module regulates rice drought tolerance by modulating the transcription of ABA- and drought-responsive genes.

Abstract

Rice (Oryza sativa L.) is a major food crop worldwide. With the acceleration of global warming, drought is becoming one of the major limitations for rice productivity. In plants, MYB transcription factors (TF) play pivotal roles in mediating drought stress tolerance. The rice OsMYB61 encodes an R2R3-MYB protein. OsMYB61 is localized both in the nucleus and the stomatal guard cells in the Nicotiana benthamiana leaves. The expression of OsMYB61 is repressed by ABA and PEG treatments. OsMYB61-overexpressing rice lines exhibited decreased drought tolerance. qRT-PCR evidence showed that the transcription levels of OsDREB2A and OsNCED1/4 in transgenic rice plants were differentially altered by PEG treatment. The yeast one-hybrid (Y1H) assay and transient luciferase reporter experiments demonstrated that OsMYB61 may bind to the promoters OsNCED1/4 and OsDREB2A, and hence inhibits their expression. OsRFP1 is a RING-finger E3 ubiquitin ligase and promotes stomatal opening. Our evidence showed that OsMYB61 interacts with and ubiquitinates OsRFP1 directly, thereby promoting its degradation via the ubiquitin-26S proteasome pathway. Moreover, knockout of OsRFP1 via the CRISPR-Cas9 technique led to decreased drought and osmotic tolerance of osrfp1 mutants, implying that OsRFP1 positively regulates drought and osmotic stress response. Furthermore, co-expression of OsRFP1 and OsMYB61 attenuated the repressive effects of OsMYB61 on the transcription of OsNCED1/4 and OsDREB2A. Collectively, our findings unraveled the molecular mechanisms of the OsRFP1-OsMYB61 module in regulating rice drought tolerance, which provide potential targets for rice breeding with improved drought tolerance.