Epsilon Archive for Student Projects

Abstract

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.