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Abscisic 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. [ABSTRACT FROM AUTHOR]

Leptosphaeria maculans is a fungal pathogen that causes blackleg disease in canola (Brassica napus), resulting in significant yield and economic losses in Canada and many parts of the world. Plant NAC transcription factors play critical roles in plant development and response to biotic or abiotic stress. In this study, we identified and characterized a BnNAC19 gene from Brassica napus. The overexpression of BnNAC19 in transgenic canola plants contributed to the improvement of seedling resistance against L. maculans. The mycelial growth of a green fluorescent protein‐tagged strain of L. maculans and production of pycnidiospores were shown to be inhibited in the transgenic canola plants overexpressing BnNAC19. In addition, the canola transgenic line overexpressing BnNAC19 showed increased disease resistance in the adult plant, which was determined by quantitative resistance. Both increased seedling and adult plant resistance in transgenic canola plants overexpressing BnNAC19 indicate that the BnNAC19 gene plays a positive role against L. maculans. The expression pattern of genes BnNAC19 upstream and downstream of BnNAC19 that participate in plant defence pathways were investigated to elucidate the B. napus resistance mechanisms to L. maculans infection, and hence to aid the long‐term blackleg disease‐resistant breeding programmes. [ABSTRACT FROM AUTHOR]