Abstract: INOSITOL-REQUIRING ENZYME 1 (IRE1) is conserved in plants and mammals to regulate stress responses. Here, we found that TaIRE1 is involved in the unconventional splicing of cell membrane-localized TabZIP60 messenger RNA (mRNA), which results in a nucleus resident protein form (TabZIP60s), and enhanced heat stress tolerance. Transcriptome analysis together with binding element prediction revealed 121 high-confidence targets of TabZIP60s responsive to heat stress in wheat (Triticum aestivum), including heat shock protein genes. Interestingly, we found that an asparagine to glutamic acid substitution, located next to DNA-binding domain of TabZIP60s, results in reduced binding affinity and transcriptional activity to downstream targets, and this heat stress tolerance inferior allele was positively selected during modern wheat breeding programs in China, possibly due to their negative effects on yield potential. Finally, we showed that TaIRE1 is also responsible for the mis-cleavage of miR172 precursors, and consequently contribute to heat stress tolerance. To the best of our knowledge, this represents the first report showing that, like in mammals, IRE1 also regulates miRNA cleavage in response to heat stress in plants. Together, this coordinate control of two signaling pathways provides new insights into heat stress tolerance regulation in wheat.

Key words: heat stress tolerance, miR172, TabZIP60, TaIRE1, wheat