The zinc-finger ubiquitin E3 ligase TaSAP5 regulates drought stress responses by promoting the degradation of DREB2A-INTERACTING PROTEIN in wheat

In Arabidopsis plants growing under normal conditions, DEHYDRATION-RESPONSIVE ELEMENT BINDING PROTEIN2A (DREB2A) is present at low levels because is ubiquitinated and destabilized by DREB2A INTERACTING PROTEIN 1 (DRIP1) and DRIP2 through 26S proteasome–mediated proteolysis. Conversely, drought stress counteracts the ubiquitination and proteolysis, thus allowing accumulation of a sufficient amount of DREB2A protein to activate downstream gene expression. The mechanisms leading to drought stress mediated DREB2A accumulation are still unclear. Here, we report that the wheat TaSAP5 protein, containing A20/AN1 domain, acts as an E3 ubiquitin ligase to mediate DRIP degradation and to increase DREB2A expression. Wheat TaSAP5 gene is inducible by drought, and TaSAP5 overexpression in Arabidopsis and wheat seedlings increased their drought tolerance as measured by survival rate and grain yield under severe drought stress. TaSAP5 interacts with and ubiquitinated AtDRIP1, AtDRIP2, and TaDRIP, leading to their subsequent degradation through the 26S proteasome pathway. Consistently, TaSAP5 overexpression enhances DRIP degradation and increases level of DREB2A protein and of its downstream targets. These results suggest that TaSAP5 acts to link drought with DREB2A accumulation and illustrate the molecular mechanisms involved in this process.