SET domain group encoding proteins function as histone lysine methyltransferases. These proteins are involved in various biological processes, including plant development and adaption to the environment by modifying the chromatin structures. So far, the SET domain genes (SDGs) have not been systematically investigated in Brassica napus (B. napus). In the current study, through genome-wide analysis, a total of 122 SDGs were identified in the B. napus genome. These BnSDGs were subdivided into seven (I–VII) classes based on phylogeny analysis, domain configurations, and motif distribution. Segmental duplication was involved in the evolution of this family, and the duplicated genes were under strong purifying selection. The promoter sequence of BnSDGs consisted of various growth, hormones, and stress-related cis-acting elements along with transcription factor binding sites (TFBSs) for 20 TF families in 59 of the 122 BnSDGs. The gene ontology (GO) analysis revealed that BnSDGs were closely associated with histone and non-histone methylation and metal binding capacity localized mostly in the nucleus. The in silico expression analysis at four developmental stages in leaf, stem root, floral organ, silique, and seed tissues showed a broad range of tissue and stage-specific expression pattern. The expression analysis under four abiotic stresses (dehydration, cold, ABA, and salinity) also provided evidence for the importance of BnSDGs in stress environments. Based on expression analysis, we performed reverse transcription-quantitative PCR for 15 target BnSDGs in eight tissues (young leaf, mature leaf, root, stem, carpel, stamen, sepal, and petals). Our results were in accordance with the in silico expression data, suggesting the importance of these genes in plant development. In conclusion, this study lays a foundation for future functional studies on SDGs in B. napus.

Brassica napus (oilseed rape) is an economically important oil crop worldwide. Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum is a threat to oilseed rape production. Because the flower petals play pivotal roles in the SSR disease cycle, it is useful to express the resistance-related genes specifically in flowers to hinder further infection with S. sclerotiorum. To screen flower-specific promoters, we first analyzed the transcriptome data from 12 different tissues of the B. napus line ZS11. In total, 249 flower-specific candidate genes with high expression in petals were identified, and the expression patterns of 30 candidate genes were verified by quantitative real-time transcription-PCR (qRT-PCR) analysis. Furthermore, two novel flower-specific promoters (FSP046 and FSP061 promoter) were identified, and the tissue specificity and continuous expression in petals were determined in transgenic Arabidopsis thaliana with fusing the promoters to β-glucuronidase (GUS)-reporter gene. GUS staining, transcript expression pattern, and GUS activity analysis indicated that FSP046 and FSP061 promoter were strictly flower-specific promoters, and FSP046 promoter had a stronger activity. The two promoters were further confirmed to be able to direct GUS expression in B. napus flowers using transient expression system. The transcriptome data and the flower-specific promoters screened in the present study will benefit fundamental research for improving the agronomic traits as well as disease and pest control in a tissue-specific manner.

In plants, phloem is not only a vital structure that is used for nutrient transportation, but it is also the location of a response that defends against various stresses, named phloem-based defense (PBD). Phloem proteins (PP2s) are among the predominant proteins in phloem, indicating their potential functional role in PBD. Sclerotinia disease (SD), which is caused by the necrotrophic fungal pathogen S. sclerotiorum (Sclerotinia sclerotiorum), is a devastating disease that affects oil crops, especially Brassica napus (B. napus), mainly by blocking nutrition and water transportation through xylem and phloem. Presently, the role of PP2s in SD resistance is still largely estimated. Therefore, in this study, we identified 62 members of the PP2 gene family in the B. napus genome with an uneven distribution across the 19 chromosomes. A phylogenetic analysis classified the BnPP2s into four clusters (I–IV), with cluster I containing the most members (28 genes) as a consequence of its frequent genome segmental duplication. A comparison of the gene structures and conserved motifs suggested that BnPP2 genes were well conserved in clusters II to IV, but were variable in cluster I. Interestingly, the motifs in different clusters displayed unique features, such as motif 6 specifically existing in cluster III and motif 1 being excluded from cluster IV. These results indicated the possible functional specification of BnPP2s. A transcriptome data analysis showed that the genes in clusters II to IV exhibited dynamic expression alternation in tissues and the stimulation of S. sclerotiorum, suggesting that they could participate in SD resistance. A GWAS analysis of a rapeseed population comprising 324 accessions identified four BnPP2 genes that were potentially responsible for SD resistance and a transgenic study that was conducted by transiently expressing BnPP2-6 in tobacco (Nicotiana tabacum) leaves validated their positive role in regulating SD resistance in terms of reduced lesion size after inoculation with S. sclerotiorum hyphal plugs. This study provides useful information on PP2 gene functions in B. napus and could aid elaborated functional studies on the PP2 gene family.

Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum (S. sclerotiorum) is the main disease threat of oilseed rape (Brassica napus), resulting in huge economic losses every year. SSR resistance manifests as quantitative disease resistance (QDR), and no gene with complete SSR resistance has been cloned or reported so far. Transcriptome analysis has revealed a large number of defense-related genes and response processes. However, the similarities and differences in the defense responses of different tissues are rarely reported. In this study, we analyzed the similarities and differences of different tissues in response to S. sclerotiorum at 24 h post inoculation (hpi) by using the published transcriptome data for respective leaf and stem inoculation. At 24 hpi, large differences in gene expression exist in leaf and stem, and there are more differentially expressed genes and larger expression differences in leaf. The leaf is more sensitive to S. sclerotiorum and shows a stronger response than stem. Different defense responses appear in the leaf and stem, and the biosynthesis of lignin, callose, lectin, chitinase, PGIP, and PR protein is activated in leaf. In the stem, lipid metabolism-mediated defense responses are obviously enhanced. For the common defense responses in both leaf and stem, the chain reactions resulting from signal transduction and biological process take the primary responsibility. This research will be beneficial to exploit the potential of different tissues in plant defense and find higher resistance levels of genotypic variability in different environments. Our results are significant in the identification of resistance genes and analysis of defense mechanisms.

Rapeseed (Brassica napus L.) is an important crop for healthy edible oil and stockfeed worldwide. However, its growth and yield are severely hampered by black rot, a destructive disease caused by Xanthomonas campestris pv. campestris (Xcc). Despite the identification of several quantitative trait loci (QTLs) associated with resistance to black rot in Brassica crops, the underlying molecular mechanisms remain largely unexplored. In this study, we investigated Xcc-induced transcriptomic and metabolic changes in the leaves of two rapeseed varieties: Westar (susceptible) and ZS5 (resistant). Our findings indicated that Xcc infection elicited more pronounced overall transcriptomic and metabolic changes in Westar compared to ZS5. Transcriptomic analyses revealed that the phenylpropanoid biosynthesis, cutin, suberine and wax biosynthesis, tryptophan metabolism, and phenylalanine metabolism were enriched in both varieties. Notably, photosynthesis was down-regulated in Westar after infection, whereas this down-regulation occurred at a later stage in ZS5. Integrated analyses of transcriptome and metabolome revealed that the tryptophan metabolism pathway was enriched in both varieties. Indolic glucosinolates and indole-3-acetic acid (IAA) are two metabolites derived from tryptophan. The expression of genes involved in the indolic glucosinolate pathway and the levels of indolic glucosinolates were significantly elevated in both varieties post-infection. Additionally, exogenous application of IAA promoted the development of black rot, whereas the use of an IAA synthesis inhibitor attenuated black rot development in both resistant and susceptible rapeseed varieties. These findings provide valuable molecular insights into the interactions between rapeseed and Xcc, facilitating the advancement of black rot resistance breeding in Brassica crops.

Plant immune genes are traditionally classified as resistance genes, susceptibility genes, or positive/negative regulators of defense. However, this framework does not fully explain a subset of immune-associated genes that display paradoxical disease phenotypes, in which genetic disruption enhances resistance despite the normal involvement of these genes in defense-related processes. GSL5/PMR4 is a representative example. As a pathogen-induced callose synthase, GSL5 contributes to papillary callose deposition and structural defense. Paradoxically, loss of GSL5 confers resistance to powdery mildew through salicylic acid- and N-hydroxypipecolic acid-associated pathways, as well as broad-spectrum resistance to Plasmodiophora brassicae through jasmonic acid-dependent immunity. Here, we refer to such genes as dual-state immune regulators, whose functional presence and genetic disruption promote resistance through distinct immune states. Similar regulatory patterns have been reported in several immune-related processes, including MAPK signaling, calcium influx, membrane trafficking, and receptor-proximal immune signaling. Representative examples include the MEKK1–MKK1/MKK2–MPK4 module, CNGC2/CNGC4, EXO70B1 and BIK1. This review uses GSL5 as a central example to discuss paradoxical immune phenotypes and dual-state immune regulators in plants, focusing on their biological features, potential mechanisms, and implications for resistance breeding.