The Sclerotinia sclerotiorum-inducible promoter pBnGH17D7 in Brassica napus: isolation, characterization, and application in host-induced gene silencing.

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, is among the most devastating diseases in Brassica napus worldwide. Conventional breeding for SSR resistance in Brassica species is challenging due to the limited availability of resistant germplasm. Therefore, genetic engineering is an attractive approach for developing SSR-resistant Brassica crops. Compared with the constitutive promoter, an S. sclerotiorum-inducible promoter would avoid ectopic expression of defense genes that may cause plant growth deficits. In this study, we generated a S. sclerotiorum-inducible promoter. pBnGH17D7, from the promoter of B. napus glycosyl hydrolase 17 gene (pBnGH17). Specifically, 5'-deletion and promoter activity analyses in transgenic Arabidopsis thaliana plants defined a 189 bp region of pBnGH17 which was indispensable for S. sclerotiorum-induced response. Compared with pBnGH17, pBnGH17D7 showed a similar response upon S. sclerotiorum infection, but lower activity in plant tissues in the absence of S. sclerotiorum infection. Moreover, we revealed that the transcription factor BnTGA7 directly binds to the TGACG motif in pBnGH17D7 to activate BnGH17. Ultimately, pBnGH17D7 was exploited for engineering Sclerotinia-resistant B. napus via host-induced gene silencing. It induces high expression of siRNAs against the S. sclerotiorum pathogenic factor gene specifically during infection, leading to increased resistance.

Genome-Wide Analysis of Myeloblastosis-Related Genes in Brassica napus L. and Positive Modulation of Osmotic Tolerance by BnMRD107.

Myeloblastosis (MYB)-related transcription factors comprise a large subfamily of the MYB family. They play significant roles in plant development and in stress responses. However, MYB-related proteins have not been comprehensively investigated in rapeseed (Brassica napus L.). In the present study, a genome-wide analysis of MYB-related transcription factors was performed in rapeseed. We identified 251 Brassica napus MYB (BnMYB)-related members, which were divided phylogenetically into five clades. Evolutionary analysis suggested that whole genome duplication and segmental duplication events have played a significant role in the expansion of BnMYB-related gene family. Selective pressure of BnMYB-related genes was estimated using the Ka/Ks ratio, which indicated that BnMYB-related genes underwent strong purifying selection during evolution. In silico analysis showed that various development-associated, phytohormone-responsive, and stress-related cis-acting regulatory elements were enriched in the promoter regions of BnMYB-related genes. Furthermore, MYB-related genes with tissue or organ-specific, stress-responsive expression patterns were identified in B. napus based on temporospatial and abiotic stress expression profiles. Among the stress-responsive MYB-related genes, BnMRD107 was strongly induced by drought stress, and was therefore selected for functional study. Rapeseed seedlings overexpressing BnMRD107 showed improved resistance to osmotic stress. Our findings not only lay a foundation for further functional characterization of BnMYB-related genes, but also provide valuable clues to determine candidate genes for future genetic improvement of B. napus.