TaHST2 silencing shapes basal heat tolerance in allohexaploid wheat

Global warming poses a substantial threat to crop productivity, yet the genetic basis of thermotolerance in wheat remains poorly understood. Here we cloned a heat stress tolerance (HST) gene, TaHST2, and revealed that it underwent functional silencing during wheat domestication. As a negative regulator of basal HST, TaHST2 was progressively suppressed through intronic sequence polymorphisms and epigenetic modifications, which might be an evolutionary consequence of hexaploidization. Haplotype analysis suggests strong artificial selection against TaHST2 expression, favouring improved thermotolerance in cultivated wheat. Further studies demonstrated that TaHST2 encodes a ubiquitin hydrolase that stabilizes HST repression proteins TaHSC701 and TaHSC702, thereby modulating heat response pathways. Our findings uncover a potential key genetic event in wheat evolution and offer new strategies for utilizing synthetic hexaploidy and octoploid wheat to breed heat-resilient varieties.