CRISPR/Cas9-based knockout of BnaLYK compromises pattern-triggered immunity and resistance to Sclerotinia sclerotiorum in Brassica napus

Rapeseed (Brassica napus) is severely threatened by Sclerotinia sclerotiorum, the causal agent of Sclerotinia stem rot (SSR). The lack of fully resistant cultivars, combined with the genetic complexity of rapeseed as an allopolyploid species, has hindered the identification of major resistance genes for molecular breeding strategies. This study identifies the involvement of BnaLYK, a LysM receptor-like kinase, in disease resistance and immune signaling pathways. The two homologs, BnaA05.LYK and BnaC05.LYK, function as orthologs of AtLYK1 in B. napus. Both genes were induced upon S. sclerotiorum infection and were localized to the plasma membrane. Heterologous expression of either gene in the atlyk1 mutant restored chitin-triggered reactive oxygen species (ROS) burst, callose deposition, and defense gene expression. CRISPR/Cas9-mediated knockout of BnaLYK significantly compromised resistance against S. sclerotiorum, characterized by increased necrotic lesion formation and decreased expression levels of defense-related genes. BnaLYK was shown to be indispensable for chitin- and peptidoglycan-induced pattern-triggered immunity, regulating ROS production, callose accumulation, and defense gene expression. Our findings demonstrate BnaLYK is essential for chitin-induced immunity and basal resistance against S. sclerotiorum in rapeseed, which underscore the conserved functionality of LysM receptors in polyploid crops and offer a promising target for breeding SSR-resistant rapeseed varieties.