The Sclerotinia sclerotiorum-inducible promoter pBnGH17 D7 in Brassica napus: isolation, characterization, and application in host-induced gene silencing

Abstract

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 means for developing SSR-resistant Brassica crops. Compared with constitutive promoter, 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 A. thaliana plants defined a 189-bp region of pBnGH17, that 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 small interfering RNAs against S. sclerotiorum pathogenic-factor gene specifically during infection, leading to increased resistance.

Natural variation in BnaA07.MKK9 confers resistance to Sclerotinia stem rot in oilseed rape

“…For S. sclerotiorum inoculation in Arabidopsis, 4-week-old unfolded leaves were detached and placed on 2 mm in diameter mycelial agar plugs for leaf inoculation following the method outlined by Lin et al 57 . The inoculated leaves were photographed and quantified at 30 hpi.…”

Genetic breakthroughs in the Brassica napus–Sclerotinia sclerotiorum interactions

“…The discovery of S. sclerotiorum-induced promoters is particularly important, and overexpression of resistance genes can enhance plant resistance and cause energy loss (Ding et al, 2021a). The promoter of glycosyl hydrolase 17 gene (pBnGH17) in rapeseed was shown to be induced by S. sclerotiorum; 5′-deletions and promoter activity analysis showed that a 189-bp region was essential for S. sclerotiorum to induce responses, and the promoter pBnGH17 D7 , which connects this region to the core promoter region, was induced after S. sclerotiorum infection, but it was less active under normal growth conditions (Lin et al, 2022). This provides an important reference for future work.…”

Fungal effectors versus defense-related genes of B. juncea and the status of resistant transgenics against fungal pathogens

“…Yield penalty is a serious issue caused by the ectopic expression of defense-related genes, so an S. sclerotiorum-induced promoter needs to be developed. In this line, Lin et al (2022) developed pBnGH17 D7 which overcame this issue. It was also used for host-induced gene silencing control of the disease.…”