Putative megaenzyme DWA1 plays essential roles in drought resistance by regulating stress-induced wax deposition in rice

Drought stress is a major limiting factor for crop production. Cuticular wax plays an important role in preventing water loss from drought stress. However, the genetic control of cuticular wax deposition under drought stress conditions has not been characterized. Here, we identified a rice gene Drought-Induced Wax Accumulation 1 (DWA1) encoding a very large protein (2,391 aa in length) containing multiple enzymatic structures, including an oxidoreductase-like domain; a prokaryotic nonribosomal peptide synthetase-like module, including an AMP-binding domain; and an allene oxide synthase-like domain. This previously unreported putative megaenzyme is conserved in vascular plants. A dwa1 KO mutant was highly sensitive to drought stress relative to the WT. DWA1 was preferentially expressed in vascular tissues and epidermal layers and strongly induced by drought stress. The dwa1 mutant was impaired in cuticular wax accumulation under drought stress, which significantly altered the cuticular wax composition of the plant, resulting in increased drought sensitivity. The mutant had reduced levels of very-long-chain fatty acids, and plants over-expressing DWA1 showed elevated levels of very-long-chain fatty acids relative to the WT. The expression of many wax-related genes was significantly suppressed in dwa1 under drought conditions. The AMP-binding domain exhibited in vitro enzymatic activity in activating long-chain fatty acids to form acyl-CoA. Our results suggest that DWA1 controls drought resistance by regulating drought-induced cuticular wax deposition in rice. This finding may have significant implications for improving the drought resistance of crop varieties.