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Clubroot, a soil-borne disease caused by Plasmodiophora brassicae, is one of the most destructive diseases of Brassica oleracea all over the world. However, the mechanism of clubroot resistance remains unclear. In this research, transcriptome sequencing was conducted on root samples from both resistant (R) and susceptible (S) B. oleracea plants infected by P. brassicae. Then the comparative analysis was carried out between the R and S samples at different time points during the infection stages to reveal clubroot resistance related pathways and candidate genes. Compared with 0 days after inoculation, a total of 4991 differential expressed genes were detected from the S pool, while only 2133 were found from the R pool. Gene function enrichment analysis found that the effector-triggered immunity played a major role in the R pool, while the pathogen-associated molecular pattern triggered immune response was stronger in the S pool. Simultaneously, candidate genes were identified through weighted gene co-expression network analysis, with Bol010786 (CNGC13) and Bol017921 (SD2-5) showing potential for conferring resistance to clubroot. The findings of this research provide valuable insights into the molecular mechanisms underlying clubroot resistance and present new avenues for further research aimed at enhancing the clubroot resistance of B. oleracea through breeding. [ABSTRACT FROM AUTHOR]

Improving Brassica napus via introgression of the genome components from its parental species, B. oleracea and B. rapa, is an important breeding strategy. Interspecific hybridization between B. napus and B. rapa is compatible with high rate of survival ovules, while the hybridization between B. napus and B. oleracea is incompatible with the high occurrence of embryo abortion. To understand the diverse embryo fate in the two interspecific hybridizations, here, the siliques of B. napus pollinated with B. oleracea (AE) and B. rapa (NE) were employed for transcriptome sequencing at 8 and 16 days after pollination. Compared to NE and the parental line of B. napus, more specific differentially expressed genes (DEGs) (1274 and 1698) were obtained in AE and the parental line of B. napus at 8 and 16 days after pollination (DAP). These numbers were 51 and 5.8 times higher than the number of specific DEGs in NE and parental line of B. napus at 8 and 16 DAP, respectively, suggesting more complex transcriptional changes in AE. Most of DEGs in the terms of cell growth and cell wall formation exhibited down-regulated expression patterns (96(down)/131(all) in AE8, 174(down)/235(all) in AE16), while most of DEGs in the processes of photosynthesis, photorespiration, peroxisome, oxidative stress, and systemic acquired resistance exhibited up-regulated expression patterns (222(up)/304(all) in AE8, 214(up)/287(all) in AE16). This is in accordance with a high level of reactive oxygen species (ROS) in the siliques of B. napus pollinated with B. oleracea. Our data suggest that the disorder of plant hormone metabolism, retardation of cell morphogenesis, and the accumulation of ROS may be associated with hybrid incompatibility between B. napus and B. oleracea. [ABSTRACT FROM AUTHOR]

Glucosinolates are amino acid‐derived secondary metabolites that act as chemical defense agents against pests. However, the presence of high levels of glucosinolates severely diminishes the nutritional value of seed meals made from rapeseed (Brassica napus L.). To identify the loci affecting seed glucosinolate content (SGC), we conducted genome‐wide resequencing in a population of 307 diverse B. napus accessions from the three B. napus ecotype groups, namely, spring, winter, and semi‐winter. These resequencing data were used for a genome‐wide association study (GWAS) to identify the loci affecting SGC. In the three ecotype groups, four common and four ecotype‐specific haplotype blocks (HBs) were significantly associated with SGC. To identify candidate genes controlling SGC, transcriptome analysis was carried out in 36 accessions showing extreme SGC values. Analyses of haplotypes, genomic variation, and candidate gene expression pointed to five and three candidate genes in the common and spring group‐specific HBs, respectively. Our expression analyses demonstrated that additive effects of the three candidate genes in the spring group‐specific HB play important roles in the SGC of B. napus. [ABSTRACT FROM AUTHOR]

Increasing clubroot resistance (CR) of Brassica oleracea by ascertaining the molecular mechanisms has been the key focus in modern B. oleracea breeding. In order to identify the quantitative trait loci (QTLs) associated with CR in B. oleracea, 94 F2 vegetative lines which were developed by tissue culture of selfed seeds from the F1 generation between a clubroot-resistant B. oleracea inbred line and a susceptible line, were identified for disease incidence and six CR-associated traits under a lab inoculation by Plasmodiophora brassicae and were genotyped with the 60K Brassica SNP array. Significant correlations were detected for numbers of fibrous roots and P. brassicae content in roots with disease incidence. Nine linkage groups were constructed from 565 bins which covered around 3,000 SNPs, spanning 1,028 cM of the B. oleracea genome with an average distance of 1.82 cM between adjacent bins. A total of 23 QTLs were identified for disease incidence and the other two correlated traits, individually explaining 6.1–17.8% of the phenotypic variation. Several overlaps were detected among traits, including one three-traits-overlapped locus on linkage group C08 and two important overlapped regions between the two CR-associated traits on C06. The QTLs were compared with known CR loci/genes and the novelty of our QTLs was discussed. [ABSTRACT FROM AUTHOR]

Sclerotinia sclerotiorum is a devastating necrotrophic plant pathogen with a worldwide distribution. Cell wall-degrading enzymes and oxalic acid are important to the virulence of this pathogen. Here, we report a novel secretory protein, Ss-Rhs1, which is essential for the virulence of S. sclerotiorum. Ss-Rhs1 is believed to contain a typical signal peptide at the N-terminal and eight rearrangement hotspot (Rhs) repeats. Ss-Rhs1 exhibited a high level of expression at the initial stage of sclerotial development, as well as during the hyphal infection process. Targeted silencing of Ss-Rhs1 resulted in abnormal colony morphology and reduced virulence on host plants. Microscopic observations indicated that Ss-Rhs1-silenced strains exhibited reduced efficiency in compound appressoria formation. [ABSTRACT FROM AUTHOR]

DNA methylation is an important regulatory mechanism for gene expression that involved in the biological processes of development and differentiation in plants. To investigate the association of DNA methylation with heterosis in Brassica, a set of intraspecific hybrids in Brassica rapa and B. napus and interspecific hybrids between B. rapa and B. napus, together with parental lines, were used to monitor alterations in cytosine methylation at 5′-CCGG sites in seedlings and buds by methylation-sensitive amplification polymorphism analysis. The methylation status of approximately a quarter of the methylation sites changed between seedlings and buds. These alterations were related closely to the genomic structure and heterozygous status among accessions. The methylation status in the majority of DNA methylation sites detected in hybrids was the same as that in at least one of the parental lines in both seedlings and buds. However, the association between patterns of cytosine methylation and heterosis varied among different traits and between tissues in hybrids of Brassica, although a few methylation loci were associated with heterosis. Our data suggest that changes in DNA methylation at 5′-CCGG sites are not associated simply with heterosis in the interspecific and intraspecific hybridizations derived from B. rapa and B. napus. [ABSTRACT FROM AUTHOR]

DNA methylation is an important regulatory mechanism for gene expression that involved in the biological processes of development and differentiation in plants. To investigate the association of DNA methylation with heterosis in Brassica, a set of intraspecific hybrids in Brassica rapa and B. napus and interspecific hybrids between B. rapa and B. napus, together with parental lines, were used to monitor alterations in cytosine methylation at 5′-CCGG sites in seedlings and buds by methylation-sensitive amplification polymorphism analysis. The methylation status of approximately a quarter of the methylation sites changed between seedlings and buds. These alterations were related closely to the genomic structure and heterozygous status among accessions. The methylation status in the majority of DNA methylation sites detected in hybrids was the same as that in at least one of the parental lines in both seedlings and buds. However, the association between patterns of cytosine methylation and heterosis varied among different traits and between tissues in hybrids of Brassica, although a few methylation loci were associated with heterosis. Our data suggest that changes in DNA methylation at 5′-CCGG sites are not associated simply with heterosis in the interspecific and intraspecific hybridizations derived from B. rapa and B. napus. [ABSTRACT FROM AUTHOR]