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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]

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Temperature is considered one of the crucial environmental elements in plant pathological interactions, and previous studies have indicated that there is a relationship between temperature change and host–pathogen interactions. The objective of this research is to investigate the link between temperature and the incompatible interactions of the host and pathogen. In this study, two Leptosphaeria maculans isolates (HCRT75 8-1 and HCRT77 7-2) and two Brassica napus genotypes (Surpass400 and 01-23-2-1) were selected. The selected B. napus genotypes displayed intermediate and resistant phenotypes. The inoculated seedlings were tested under three temperature conditions: 16 °C/10 °C, 22 °C/16 °C and 28 °C/22 °C (day/night: 16 h/8 h). Lesion measurements demonstrated that the necrotic lesions from the 28 °C/22 °C treatment were enlarged compared with the other two temperature treatments (i.e., 16 °C/10 °C and 22 °C/16 °C). The results of expression analysis indicated that the three temperature treatments displayed distinct differences in two marker genes (PATHOGENESIS–RELATED (PR) 1 and 2) for plant defense and one temperature-sensitive gene BONZAI 1 (BON1). Additionally, seven dpi at 22 °C/16 °C appeared to be the optimal pre-condition for the induction of PR1 and 2. These findings suggest that B. napus responds to temperature changes when infected with L. maculans. [ABSTRACT FROM AUTHOR]

Global warming by increased atmospheric CO2 concentration has been widely accepted. Yet, there has not been any consistent conclusion on the doubled CO2 concentration that in the future will affect plant disease incidence and severity. Blackleg disease, mainly caused by Leptosphaeria maculans, is a major disease on canola production globally. Brassica napus and L. maculans have a gene-for-gene interaction, which causes an incompatible reaction between canola plants carrying resistance genes and L. maculans isolates carrying corresponding avirulence genes. In this study, B. napus varieties and lines inoculated with different Leptosphaeria isolates were subjected to simulated growth conditions, namely, growth chambers with normal environments and with controlled CO2 concentrations of 400, 600, and 800 ppm. The results indicated that the elevated CO2 concentrations have no noticeable effect on the inferred phenotypes of the canola–blackleg interactions. However, the disease severity decreased in most of the B. napus–L. maculans interactions at extremely high CO2 concentration (800 ppm). The varied pathogenicity changes of the B. napus–L. maculans pathosystem under elevated CO2 concentrations at 400 or 600 ppm may be due to the genetic background or physiological differences in plants and pathogenicity differences in L. maculans isolates having different Avr gene profiles. The mechanisms by which elevated CO2 concentrations affect the B. napus–L. maculans pathosystem will help us understand how climate change will impact crops and diseases. [ABSTRACT FROM AUTHOR]

Blackleg (Phoma stem canker) of crucifers is a globally important disease caused by the ascomycete species complex comprising of Leptosphaeria maculans and Leptosphaeria biglobosa. Six blackleg isolates recovered from Brassica rapa cv. Mizspoona in the Willamette Valley of Oregon were characterized as L. biglobosa based on standard pathogenicity tests and molecular phylogenetic analysis. These isolates were compared to 88 characterized L. biglobosa isolates from western Canada, 22 isolates from Australia, and 6 L. maculans isolates from Idaho, USA using maximum parsimony and distance analysis of phylogenetic trees generated from the ITS rDNA (internal transcribed spacer rDNA) sequence, and the actin and β-tubulin gene sequences. The L. biglobosa isolates derived from B. rapa collected in Oregon formed a separate subclade based on concatenated gene sequences or a single gene sequence, regardless of the analyses. Pathogenicity tests showed that these isolates failed to infect either resistant or susceptible B. napus cultivars, but caused severe symptoms on three B. rapa cultivars (Accession number: UM1113, UM1112, and UM1161), a B. oleracea var. capitata (cabbage) cultivar (Copenhagen Market), and two B. juncea cultivars (CBM, a common brown Mustard, and Forge). These findings demonstrated that the L. biglobosa isolates derived from a B. rapa crop in Oregon were genetically distinct from existing species of L. biglobosa, and constitute a new subclade, herein proposed as L. biglobosa 'americensis'. [ABSTRACT FROM AUTHOR]

Callose plays a critical role in different biological processes including development as well as in the response to multiple biotic and abiotic stresses. In this study, we characterized the callose deposition in cotyledons of different Brassica napus varieties post-inoculated with different Leptosphaeria maculans isolates. Further, members of the callose synthase gene were identified from the whole genome of B. napus using the 12 Arabidopsis thaniana callose synthase protein sequences, and were then classified into three groups based on their phylogenetic relationships. Chromosomal location and duplication patterns indicated uneven distribution and segmental duplication patterns of BnCalS genes in the B. napus genome. Subsequently, gene structures, conserved domains analysis, and protein properties were analyzed for BnCalS genes. In addition, 12 B. napus orthologs of the AtCalS were selected for investigating the tissue expression pattern, indicating diverse expression patterns for these BnCalS genes. Responses of the selected 12 orthologs and all the BnCalS genes were characterized in the different types (AvrLm1-Rlm1, AvrLm4-Rlm4, AvrLepR1-LepR1) of B. napus–L. maculans interactions and B. napus-Leptosphaeria biglobosa interactions, implying their potential roles in response to Leptosphaeria infection. [ABSTRACT FROM AUTHOR]

• LmCBP1 is a secreted protein and can bind to chitin. • Knockout of LmCBP1 in Leptosphaeria maculans using CRISPR-Cas9 lowered the pathogenicity of this pathogen on Brassica napus. • The knockout mutants of LmCBP1 were more sensitive to hydrogen peroxide. Leptosphaeria maculan s is the causal agent of blackleg disease on Brassica napus. Determining the underlying functions of genes required for pathogenesis is essential for understanding the infection process. A chitin-binding protein (LmCBP1) was discovered as a pathogenicity factor for the infection of B. napus by L. maculans through gene knockout using the CRISPR-Cas9 system. Chitin-binding activity was demonstrated through a chitin-protein binding assay. A secreted signal peptide was detected using a yeast secreted-signal peptide trap assay. An increased expression level during the infection stage was also observed, suggesting that LmCBP1 is a secreted protein. The knockout mutants showed decreased infection on B. napus , with reduced pathogenicity on ten cultivars with/without diverse R genes. The mutants were more sensitive to H 2 O 2 compared to wild type L. maculans isolate JN3. This study provides evidence of the virulence of a novel chitin-binding protein LmCBP1 on B. napus through mutants created via the CRISPR-Cas9 system. [ABSTRACT FROM AUTHOR]