Host-induced gene silencing of multiple pathogenic factors of Sclerotinia sclerotiorum confers resistance to Sclerotinia rot in Brassica napus

Sclerotinia sclerotiorum is generally considered one of the most economically damaging pathogens in oilseed rape (Brassica napus). Breeding for Sclerotinia resistance is challenging, as no immune germplasm available in B. napus. It is desirable to develop new breeding strategies. In the present study, host-induced gene silencing (HIGS), developed based on RNA interference (RNAi), was applied to protect B. napus from S. sclerotiorum infection. Three pathogenicity genes, the endo-polygalacturonase gene (SsPG1), cellobiohydrolase gene (SsCBH), and oxaloacetate acetylhydrolase gene (SsOAH1), were chosen as HIGS targets. Co-incubation of synthesized double-stranded RNAs (dsRNAs) with S. sclerotiorum in liquid medium significantly reduced the transcript levels of the target genes. Application to plant surfaces of dsRNA targeting the three genes conferred effective protection against S. sclerotiorum. Stable transgenic B. napus plants expressing small interfering RNAs with sequence identity to SsPG1, SsCBH, and SsOAH1 were generated. HIGS transgenic B. napus prevented the expression of S. sclerotiorum target genes, slowed pathogenicity-factor accumulation, impeded fungal growth, and suppressed appressorium formation, thereby conferring resistance to S. sclerotiorum. Simultaneous silencing of SsPG1, SsCBH, and SsOAH1 by stable expression of a chimeric hairpin RNAi construct in B. napus led to enhanced protection phenotypes (with disease lesion size reduced by 36.8%–43.7%). We conclude that HIGS of pathogenic-factor genes of S. sclerotiorum is a promising strategy for controlling Sclerotinia rot in oilseed rape.