Regulated gene silencing in the fungal pathogen Ophiostoma novo-ulmi

Ophiostoma novo-ulmi is the third most devastating fungal pathogen in Canada, affecting native Ulmus spp. Control efforts are pursuing a gene regulation approach, using RNAi cassettes driven by constitutive heterologous promoters to evaluate virulence-related genes. A homologous carbon-catabolite regulated promoter (alcA) was developed for a cassette that regulates endopolygalacturonase (EPG) expression. Using the YFP reporter to assess promoter functionality, expression was repressed under glucose, released with its depletion and not repressed under glycerol. The EPG-alcA-RNAi cassette was similarly inactive under glucose, but highly expressed following glucose depletion, reducing EPG expression by 80–100%. Transfer to glucose medium restored native EPG expression as RNAi was down-regulated. This demonstration of RNAi regulation by carbon source offers a promising tool to evaluate gene functionality.

► A carbon-catabolite regulated promoter was developed based on the alcA gene.
► This is the first endogenous promoter developed for this important tree pathogen.
► This promoter was used for regulated expression of EPG-RNA interference cassettes.
► RNAi expression may selectively inactivate gene targets by glucose starvation.
► This construct provides a robust tool to determine gene function in Ophiostoma.