Overexpression of Transcription Factor OsWR2 Regulates Wax and Cutin Biosynthesis in Rice and Enhances its Tolerance to Water Deficit

Drought is the major abiotic stress limiting crop production. Plant cuticle represents the outer-most layer of the epidermis and plays an important role in decreasing plant water loss under drought stress by restricting non-stomatal transpiration. We report here that the Wax Synthesis Regulatory 2 gene (OsWR2) in rice (Oryza sativa L.) is highly expressed in epidermal tissues and contributes to the transcriptional regulation of both cuticular wax and cutin biosynthesis in rice cuticle. Overexpression of OsWR2 in rice increased the total cuticular wax level by 48.6 % in leaves and by 72.4 % in panicles. Of the major wax classes, aldehydes increased most in leaves, and alkanes increased most in panicles. Total cutin amounts were increased by 48.1 % in leaves and 65.9 % in panicles of rice overexpressing OsWR2, and these increases were due primarily to the increase in omega-OH and di-OH acids. Our results showed that 19 genes previously associated with wax and cutin biosynthesis were up-regulated in OsWR2 overexpressors. Overexpression of OsWR2 also altered cuticular wax crystallization and cuticle membrane ultrastructure. Furthermore, OsWR2 overexpression in rice decreased leaf chlorophyll leaching rate, reduced water loss rate, and enhanced tolerance to water-limited conditions. We demonstrate in this report that OsWR2 regulates wax and cutin biosynthesis differently than does the OsWR1 homologue, and plays a major role in controlling cuticle permeability. The increased resistance to water deficit conditions by OsWR2 overexpression in rice elucidates a potential new strategy for genetic improvement of plant drought tolerance.