Identification of BnaAOS in Brassica napus and its regulatory effect on resistance to Sclerotinia sclerotiorum

INTRODUCTION: Sclerotinia sclerotiorum is a destructive fungal pathogen that severely threatens the production of Brassica napus. Jasmonic acid (JA) signaling plays a central role in plant defense against necrotrophic pathogens. Allene oxide synthase (AOS) is a key rate-limiting enzyme in JA biosynthesis; however, its function in rapeseed resistance to S. sclerotiorum remains unclear. RATIONALE: RATIONALE: Previous studies have demonstrated that AOS contributes to disease resistance in model plants, but its role in B. napus has not been systematically investigated. We hypothesized that BnaAOS genes participate in JA-mediated defense against S. sclerotiorum. To test this, we combined gene identification, expression analysis, and heterologous genetic approaches to study its function. RESULTS: Two AOS homologs, BnaA02.AOS and BnaC02.AOS, were identified in B. napus, both encoding conserved proteins localized in chloroplasts. Expression analysis revealed that BnaAOS and AtAOS were significantly induced at the late stages of infection. Moreover, JA signaling-related genes (MYC2 and PDF1.2) were upregulated in response to pathogen invasion. Genetic analysis in Arabidopsis thaliana showed that the aos mutant exhibited increased susceptibility, whereas AtAOS overexpression enhanced its resistance to S. sclerotiorum. Importantly, heterologous expression of BnaAOS restored both fertility and disease resistance in the aos mutant, demonstrating the functional equivalence of BnaAOS in A. thaliana. CONCLUSION: Our results indicate that AOS positively regulates plant resistance to S. sclerotiorum through JA-mediated defense pathways. The functional conservation of BnaAOS highlights its role as a key component in JA biosynthesis, and provides a foundation for disease resistance management in rapeseed.