P-351 - Spatial Dynamics of Host Defense Responses during Sclerotinia sclerotiorum infection in Canola

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, poses a global threat to crops such as canola (Brassica napus). This necrotrophic pathogen undermines host immunity to establish infection and promote tissue colonization. We investigated the plant-pathogen interactions across distinct tissue regions (necrotic, margin, and uninfected zones) to elucidate the spatially regulated defense responses. Notably, the margin zone, where defense activation is critical, showed more pronounced chlorosis in canola leaves infected with the oxalate-deficient S. sclerotinia mutant (M202) than the wild-type strain. Transcriptomic analysis revealed a localized upregulation of defense-related genes and light-harvesting complex precursors in the margin zone. These findings were validated by quantitative RT-PCR, which confirmed differential expression of salicylic acid and jasmonic acid marker genes. Metabolic profiling showed a significant increase in photoprotective metabolites involved in the xanthophyll cycle, specifically in the margin and necrotic zones during wild-type infection, and mainly in the margin zone during mutant-type infection, potentially impacting host immunity. Additionally, genes involved in abscisic acid biosynthesis (e.g., AAO, and NCED3) exhibited zone-specific expression, with higher expression in the margin zone during M202 infection and broader expression during wild-type infection. These findings provide new insights into spatially regulated defense mechanisms against S. sclerotiorum and offer potential targets for improving plant resistance.