XBAT31 regulates reproductive thermotolerance through controlling the accumulation of HSFB2a/B2b under heat stress conditions

Heat shock transcription factors (HSFs) play a crucial role in heat stress tolerance in vegetative tissues. However, their involvement in reproductive tissues and their post-translational modifications are not well understood. In this study, we identify the E3 ligase XB3 ORTHOLOG 1 IN ARABIDOPSIS THALIANA (XBAT31) as a key player in the ubiquitination and degradation of HSFB2a/B2b. Our results show that the xbat31 mutant exhibits a higher percentage of unfertile siliques and decreased expression of HSPs in flowers under heat stress conditions compared to the wild type. Conversely, the hsfb2a hsfb2b double mutant displays improved reproductive thermotolerance. We find that XBAT31 interacts with HSFB2a/B2b and mediates their ubiquitination. Furthermore, HSFB2a/B2b ubiquitination is reduced in the xbat31-1 mutant, resulting in higher accumulation of HSFB2a/B2b in flowers under heat stress conditions. Overexpression of HSFB2a or HSFB2b leads to an increase in unfertile siliques under heat stress conditions. Thus, our results dissect the important role of the XBAT31-HSFB2a/B2b module in conferring reproductive thermotolerance in plants. [Display omitted] •XBAT31 positively regulates reproductive thermotolerance•XBAT31 interacts with and ubiquitinates HSFB2a/B2b•XBAT31 suppresses HSFB2a/B2b accumulation in flower buds Zhang et al. show that the XBAT31-HSFB2a/B2b module plays an important role in maintaining fertility under heat stress conditions. They show that XBAT31 interacts with HSFB2a/B2b to mediate their ubiquitination and degradation. Thus, XBAT31 suppresses transcriptional repressors such as HSFB2a/B2b to promote stress-responsive gene expression and confer reproductive thermotolerance.