Subcellular localization and kinase activity of GK4, a Phytophthora infestans GPCR-PIPK involved in actin cytoskeleton organisation

For dispersal and host infection plant pathogens largely depend on asexual spores. Pathogenesis and sporulation are complex processes that are governed by various cellular signaling networks including G-protein and phospholipid signaling. Oomycetes possess a family of novel proteins called GPCR-PIPKs (GKs) that are composed of a seven transmembrane spanning (7-TM) domain fused to a phosphatidylinositol phosphate kinase (PIPK) domain. Based on this domain structure GKs are anticipated to link G-protein and phospholipid signalling pathways. Our studies in the potato late blight pathogen Phytophthora infestans revealed involvement of one of twelve GKs (i.e. PiGK4) in spore development, hyphal elongation and infection. Moreover, ectopic expression in P. infestans of subdomains of PiGK1 and PiGK4 fused to a fluorescent protein showed that the GPCR domain targets the GKs to membranes surrounding different cellular compartments. To further elucidate the function of the PIPK domain we tested kinase activity of PiGK4 both in vivo and in vitro and analysed the relationship between PiGK4, phosphoinositide signaling and the organisation of the actin cytoskeleton using complementation in yeast combined with various live-cell markers.