Multilevel Characterization Reveals Divergent Heat Responses Among Diploid, Tetraploid, and Hexaploid Wheat Genotypes

Understanding heat stress (HS) responses in wheat is important for breeding varieties adapted to increasing temperature. HS during grain filling reduces wheat yield, but transcriptional and alternative-splicing responses among wheat genotypes of different ploidy remain poorly characterized. We conducted two field experiments with diploid Triticum monococcum, tetraploid T. turgidum subsp. durum, and hexaploid T. aestivum. In Exp. 2, one genotype per species was exposed to severe HS for four consecutive days beginning 10 days after anthesis, and grains were sampled for RNA sequencing 3 h after treatment onset. Mean grain yield declined by 59.4%, 19.0%, and 37.9% in the diploid, tetraploid, and hexaploid genotypes, respectively, accompanied by reductions in thousand-grain weight. After homoeolog grouping, the tetraploid genotype had the smallest fraction of heat-responsive groups and the hexaploid the largest. HS also altered alternative splicing, with broader functional enrichment in the hexaploid genotype. In this genotype, all three homoeologs of an NF-YB gene showed heat-induced skipping of exon E6, and the splice products of the D-genome locus were confirmed by RT-PCR and Sanger sequencing. These results show that the three examined genotypes differed in phenotypic, transcriptional, and splicing responses to HS and identify NF-YB splicing as a candidate component of the hexaploid grain response. Main conclusionEarly grain-filling heating reduced yield and altered transcription and splicing in the three examined wheat genotypes, including increased NF-YB exon E6 skipping in the hexaploid wheat genotype.