Phosphatidylinositides defining effector protein delivery in Phytophthora

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Oomycete plant pathogens, exemplified by the potato and tomato late blight pathogen Phytophthora infestans, cause some of the most destructive crop diseases. Infection is driven by delivery of effector proteins into host tissues. In Phytophthora, effectors can be secreted via at least two different pathways. Protein secretion involves coordination of specialised membranous organelles and vesicles. Membranes can be differentiated by the presence of specific phosphatidylinositol phosphates (PtdIns) that are interconverted by lipid kinases and phosphatases. Inhibition of the kinases and phosphatases that synthesise PtdIns can potentially disrupt membrane trafficking, block effector protein secretion and control disease. The occurrence and localisations of PtdIns and their associated PtdIns kinases (PIKs) and phosphatases are largely unknown in Phytophthora.

We propose to use PtdIns binding proteins, fused to fluorescent proteins, as biosensors in P. infestans to reveal which PtdIns are present in secretory pathways. We will localise infection-up-regulated lipid kinases/phosphatases to reveal major sites of PtdIns modification during infection, and their association with secretory pathways. PtdIns-4-kinases (PI4Ks) and PI3Ks are potentially associated with secretory pathways, thus we will use pan-PI4K/PI3K and Phytophthora-specific PI4K inhibitors to determine their impact on effector secretion pathways in P. infestans. Finally, we will use gene silencing to remove the activity of specific infection up-regulated PI4Ks, PI3K and phosphatases to determine their importance for pathogenicity and effector secretion in P. infestans, thus providing potential targets for agrochemical control.