Two G protein-coupled receptors with a phosphatidylinositol phosphate kinase domain have a role in asexual and sexual developments in Phytophthora sojae

G protein-coupled receptors (GPCRs) are cellular key components that mediate mostly extracellular signals into intracellular responses. They share an architecture consisting of seven transmembrane domains with a, at the cytosolic side located, C-terminal tail that initiates downstream signaling. A novel class of GPCRs exist in oomycetes that have a phosphatidylinositol phosphate kinase (PIPK) domain fused their C-terminus. Phytophthora species contain twelve GPCR-PIPKs (GK1-GK12). The present study focusses on two P. sojae GKs. Expression analysis revealed that PsGK4 and PsGK5 are differentially expressed during some development stages. The expression levels of PsGK4 and PsGK5 are peaking at the cyst stage or during cyst germination and during late infection stages. Functional analysis of PsGK4 and PsGK5 was accomplished by obtaining silenced transformants. Whereas The PsGK4 silenced transformants exhibited no difference in hyphae morphology, growth rate and oospore production in comparison to wild type and control transformants, they showed a higher level of encystment and a reduced cyst germination rate. In addition, zoospores lost the chemotaxis response to soybean root tips. The PsGK5 silenced transformants exhibited no differences in asexual development. Instead, the oospore production of silenced transformants was severely impaired. Both PsGK4 and PsGK5-silenced transformants showed reduced pathogenicity. RFP fusions of GK5 revealed the absence of the protein from the transmembrane but its presence in small vesicles of which a significant fraction moved rapidly. The obtained results point to involvement of GKs during various life-stages regulating zoospore behavior and oospore development. We propose that each of the GKs heads a pathway involved in development.