BnaA07.WRKY40 transcription factor confers enhanced defensive response to Sclerotinia sclerotiorum in Brassica napus.

Oilseed rape (Brassica napus, B. napus) is one of the most important oil crops globally, contributing significantly to the world's supply of vegetable oil. However, its production is severely threatened by Sclerotinia stem rot, a disease caused by the broad-host-range fungus Sclerotinia sclerotiorum (Lib.) de Bary (S. sclerotiorum). Despite extensive research efforts, the identification of defense genes in B. napus remains limited, underscoring the urgent need to discover more robust and functional genes that confer effective defense against this pathogen. In this study, we demonstrate that BnaA07.WRKY401 acts as a positive regulator in response to S. sclerotiorum infection. The expression of BnaA07.WRKY40 is highly induced following exposure to S. sclerotiorum, and its overexpression in B. napus markedly enhance plant defense against Sclerotinia stem rot. In contrast, BnaA07.WRKY40-RNAi and knockout mutants displayed increased susceptibility to S. sclerotiorum. Yeast two-hybrid and luciferase complementation imaging assays suggest that BnaA07.WRKY40 proteins may function by forming homodimers. Further insights into the role of BnaA07.WRKY40 is gained through DAP-Seq and RNA-Seq analyses, complemented by yeast one-hybrid assay. It is revealed that BnaA07.WRKY40 regulates downstream target genes encoding Hypoxia-responsive family protein (HRP), β-1,3-glucanase 2 (BG2), Precursor of peptide 1 (PEP1), and Acyl-CoA N-acyltransferase (ACNAT) superfamily protein. Following S. sclerotiorum inoculation, the lesion areas on the leaves of mutants for these target genes were significantly larger than those on wild-type plants, indicating that knockout of these genes increased susceptibility to S. sclerotiorum. These findings provide valuable insights into the molecular mechanisms by which BnaA07.WRKY40 regulates defensive response to Sclerotinia stem rot and offer new avenues for the molecular breeding of oilseed rape with enhanced resistance to S. sclerotiorum.