The gene encoding flavonol synthase contributes to lesion mimic in wheat

Lesion mimic often exhibits leaf disease-like symptoms even in the absence of pathogen infection, and is characterized by a hypersensitive-response (HR) that closely linked to plant disease resistance. Despite this, only a few lesion mimic genes have been identified in wheat. In this investigation, a lesion mimic wheat mutant named je0297 was discovered, showing no alteration in yield components when compared to the wild type (WT). Segregation ratio analysis of the F2 individuals resulting from the cross between the WT and the mutant revealed that the lesion mimic was governed by a single recessive gene in je0297. Using Bulked segregant analysis (BSA) and exome capture sequencing, we mapped the lesion mimic gene designated as lm6 to chromosome 6BL. Further gene fine mapping using 3315 F2 individuals delimited the lm6 within a 1.18 Mb region. Within this region, we identified 16 high-confidence genes, with only two displaying mutations in je0297. Notably, one of the two genes, responsible for encoding flavonol synthase, exhibited altered expression levels. Subsequent phenotype analysis of TILLING mutants confirmed that the gene encoding flavonol synthase was indeed the causal gene for lm6. Transcriptome sequencing analysis revealed that the DEGs between the WT and mutant were significantly enriched in KEGG pathways related to flavonoid biosynthesis, including flavone and flavonol biosynthesis, isoflavonoid biosynthesis, and flavonoid biosynthesis pathways. Furthermore, more than 30 pathogen infection-related (PR) genes exhibited upregulation in the mutant. Corresponding to this expression pattern, the flavonoid content in je0297 showed a significant decrease in the 4th leaf, accompanied by a notable accumulation of reactive oxygen, which likely contributed to the development of lesion mimic in the mutant. This investigation enhances our comprehension of cell death signaling pathways and provides a valuable gene resource for the breeding of disease-resistant wheat.