Characterization, genetic analysis and gene identification of an EMS-mutagenized lesion-mimic mutant with enhanced powdery mildew resistance in bread wheat (Triticum aestivum L.).

Lesion mimic mutants (LMMs) are ideal for dissecting plant immunity mechanisms. Here, we characterized lm10373, a stable LMM isolated from an EMS-induced library of wheat cultivar AK58. lm10373 developed light-dependent lesion spots on leaves from the late tillering stage, accompanied by programmed cell death (PCD) and reactive oxygen species (ROS) accumulation. Phenotypically, lm10373 showed reduced photosynthetic capacity and yield-related traits, but enhanced powdery mildew resistance at the heading stage. Genetic analysis revealed the lesion trait was controlled by a single semi-dominant nuclear gene, mapped to a 35 Mb interval on chromosome 3B via bulked segregant analysis coupled with exome capture sequencing (BSE-seq). Integrating exome sequencing and transcriptome data, we identified TaWSD1-3B (encoding an O-acyltransferase of the WSD1 family) as the causal gene. A G-to-A mutation (p.Ala79Thr) in its conserved acyltransferase domain introduced a new phosphorylation site, disrupting triacylglycerol biosynthesis. Two independent mutants (lm129, p.Arg207His; lm295, 3'UTR mutation) validated TaWSD1-3B function. Haplotype analysis of 183 wheat accessions identified three TaWSD1-3B haplotypes: Hap1 was associated with higher 1000-grain weight and lower leaf tip necrosis (LTN) severity, making it a favorable allele for breeding. This study characterized a wheat LMM mutant and candidate gene TaWSD1-3B, suggesting a lipid-ROS-PCD pathway regulating immunity, and provides valuable markers for stress-tolerant, high-yield wheat breeding.