Transcriptome sequencing reveals hotspot mutation regions and dwarfing mechanisms in wheat mutants induced by γ-ray irradiation and EMS.

Induced mutation is an important approach for creating novel plant germplasms. The introduction of dwarf or semi-dwarf genes into wheat has led to great advancements in yield improvement. In this study, four elite dwarf wheat mutants, named dm1-dm4, induced from γ-ray irradiation or ethyl methanesulfonate (EMS) mutagenesis, were used to identify transcriptome variations and dwarfing mechanisms. The results showed that the hotspot regions of mutations distributed on the chromosomes were consistent among the four mutant lines and these regions were mainly located around the 50, 360 and 400 Mb positions of chromosome 1A and the distal regions of chromosomes 2A and 2BL. Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggested that 'protein processing in endoplasmic reticulum' was the most common significantly enriched pathway based on the differentially expressed genes (DEGs) between wildtype (WT) and the mutants. Notably, 18 out of 20 genes involved in this process encode heat shock proteins (HSPs). The results implied that HSPs might participate in wheat dwarfism response and function in the dwarfism process through protein folding and/or degradation. Moreover, seven genes in dm4 involved in modulating auxin levels were down-regulated and dm4 was more sensitive to auxin treatment compared with WT, indicating the important roles of auxin in regulation of dwarf phenotype in dm4. This study not only identified transcriptome sequence variation induced by physical and chemical mutagenesis but also revealed potential dwarfing mechanisms in the wheat mutant lines.