Natural Variation in TaFAD8-D Promoter Enhances Thermotolerance in Wheat Through Fatty Acid and Lipid Remodelling.

Heat stress (HS) has become an increasing threat to wheat productivity under global warming. However, the genetic loci for thermotolerance and the underlying molecular mechanisms remain largely unknown. In this study, genetic mapping identified a thermotolerance locus, QMpe.cau-2D, encoding fatty acid desaturase 8 (FAD8), with the transposable element (TE) insertions present in the promoter region in the thermotolerant cultivar. The expression of TaFAD8-D was negatively associated with thermotolerance. Loss-of-function mutations in TaFAD8 enhanced photosynthetic efficiency, seedling survival rate, and thousand-grain weight under HS. Transcriptome, fatty acid, and lipid profiling analyses showed that TaFAD8 mutation affected the expression of genes involved in lipid biosynthesis and metabolism to mediate the fatty acid composition and lipid remodelling, thereby maintaining chloroplast membrane fluidity and integrity under HS. TaWRKY71 negatively regulated the transcription of TaFAD8 by binding to its promoter, and mutation of TaWRKY71 reduced photosynthetic efficiency under HS. Our findings identify a beneficial TaFAD8-D haplotype, uncover its molecular mechanism and regulatory pathways in heat response, and provide a strategy for breeding climate-resilient wheat varieties.