BnTX1–BnNCED3 interaction contributes to the ABA biosynthesis response in the Brassica napus–Leptosphaeria maculans pathosystem

AbstractAbscisic acid (ABA) plays multiple and pivotal roles in plant defence against abiotic and biotic stresses. Blackleg, mainly caused by the fungal pathogen Leptosphaeria maculans, is one of the most devastating diseases in canola (Brassica napus) resulting in significant yield loss worldwide. Few studies have investigated the function of ABA biosynthesis genes in response to fungal pathogens. In this study, we identified and characterized BnNCED3 (9‐cis‐epoxycarotenoid dioxygenease) and BnTX1 (trithorax‐like factor) from B. napus. Transgenic B. napus ‘Westar’ plants overexpressing BnNCED3 showed enhanced adult plant resistance to blackleg infection. Chromatin immunoprecipitation‐quantitative PCR demonstrated that BnTX1 bound to the promoter region of the BnNCED3 gene. However, the overexpression of BnTX1 in transgenic plants decreased adult plant resistance to blackleg pathogen infection. The expression analysis confirmed the abundance of BnNCED3 transcripts was higher in BnTX1‐RNAi knockdown plants than in overexpressing plants. Thus, BnTX1 might play a negative role in regulating BnNCED3 gene expression and hence ABA biosynthesis, thereby affecting plant disease resistance. Our study provides a new model demonstrating how increased ABA levels can enhance plant disease resistance, which may lead to the characterization of minor/quantitative genes in the B. napus–L. maculans interaction.