Genome-Wide Analysis of BnaRLCK VII Gene Family in Brassica napus and Investigation of Its Function in Resistance to Sclerotinia sclerotiorum

Receptor-like cytoplasmic kinases (RLCKs) constitute a core family of signaling proteins that modulate diverse cellular activities and participate in multiple physiological and biochemical processes in plants. As a unique subclade of RLCKs, the receptor-like cytoplasmic kinases VII (RLCK VII) subfamily features a conserved kinase domain but lacks extracellular and transmembrane domains, and has been proven to exert crucial functions in plant immunity, growth and development, and yield formation. Background/Objectives: This study systematically identified and characterized RLCK VII family genes in the rapeseed (Brassica napus) genome, and explored their biological functions in plant resistance to Sclerotinia sclerotiorum. Methods: Multiple bioinformatics databases and online tools were employed to conduct a comprehensive analysis of the identified BnaRLCK VII genes, including their physicochemical properties, signal peptide characteristics, subcellular localization, phylogenetic relationships, gene structure, conserved motifs and domains, cis-regulatory elements, tissue-specific expression patterns, and gene duplication events. Transcriptome profiling (RNA-seq) and transient overexpression assays in Nicotiana tabacum were further performed to verify the function of BnaRLCK VII genes in S. sclerotiorum resistance. Results: A total of 173 RLCK VII family members were identified from the B. napus genome and designated as BnaRLCK VII genes. These genes were clustered into 10 distinct subgroups based on phylogenetic analysis. We further comprehensively analyzed their gene structures, conserved motifs, cis-acting elements, duplication patterns, and tissue expression profiles. RNA-seq analysis revealed that 31 BnaRLCK VII genes were significantly differentially expressed following S. sclerotiorum infection. Among these differentially expressed genes (DEGs), a homolog of Arabidopsis thaliana BIK1 was selected for functional validation and named BnaBIK1. Agrobacterium-mediated transient infiltration assays on tobacco leaves demonstrated that overexpression of BnaBIK1 could improve plant tolerance to S. sclerotiorum, which indicates that BnaBIK1 is a promising candidate gene for regulating rapeseed resistance against this pathogen. Conclusions: Collectively, these findings indicate that BnaRLCK VII family genes, particularly BnaBIK1, serve as key positive regulators of S. sclerotiorum resistance in B. napus.