Spray Induced Gene Silencing in Phytophthora infestans : investigating exogenous dsRNA application for the control of potato late blight

Sammanfattning: Phytophthora infestans is an oomycete pathogen and the causal agent of late blight disease in potato and tomato. Even today, it causes massive loss to crop and economy worldwide. Current disease control strategies include breeding for resistance and extensive fungicide spray. However, fungicides raise serious environmental concerns and include the risk of P. infestans developing resistance. Previously, RNA interference has been successfully employed to control the disease severity through a transgenic approach known as host-induced gene silencing. In this study, we exploit the RNAi mechanism in an alternative, non-transgenic way through a method called sprayinduced gene silencing (SIGS). To achieve reduced disease progression, SIGS utilizes double stranded RNA (dsRNA) in the form of a foliar spray to target pathogen genes important for growth and infection. We targeted five genes in P. infestans. The guanine-nucleotide binding protein βsubunit (PiGPB1) is important in sporangia formation, the oxysterol binding protein (PiOSBP) is a fungicide target and the haustorial membrane protein (PiHmp1) is important to establish infection. In addition, the carbohydrate-active enzymes cutinase (PiCut3) & endo-1,3(4)-β-glucanase (PiEndo3) are essential for penetration and colonization of the host tissue. Through confocal imaging, we have provided a proof of concept that in vitro synthesized dsRNA is taken up by P. infestans sporangia from surrounding environment and dsRNA sprayed leaves. We then show that targeted dsRNA spray reduces P. infestans disease progression through detached leaf assay. The varying degree of disease reduction observed in the different dsRNA treatments indicated that the efficiency of SIGS relies on the selection of target genes. Thus, we conclude that target-specific gene silencing using SIGS can be a potential methodology to sustainably control potato late blight.