The inositol polyphosphate phosphatase family in oomycetes

Phosphoinositides (PIs) play essential roles in intracellular transport and communication. They function as membrane signalling molecules and modulate the activity of a plethora of proteins. Eukaryotic cells harbour seven distinct PI isoforms, the levels of which are governed by the activity of PI kinases (PIKs and PIPKs) and inositol polyphosphate phosphatases (INPPs) that rapidly convert one PI into another. Previously we identified a unique repertoire of PI(P)Ks in Phytophthora spp. including twelve GPCR-PIPKs (GKs) composed of a N-terminal G-protein-coupled-receptor (GPCR) domain fused to a PIPK catalytic domain. GK4 and GK5 have been shown to be involved in developmental transitions in Phytophthora (Yang et al. 2013, Mol. Microbiol.; Hua et al. 2013, Mol. Microbiol.). Here we focus on Phytophthora INPP genes. A genome-wide inventory of Phytophthora spp. and other oomycetes revealed that most genomes encode around 22 distinct INPPs. They are well conserved in their catalytic domains and correlate to the known INPPs classes (INPP3, -4, -5 and SAC-like lipid phosphatases). However, in a subset of the INPPs the catalytic region, either INPP4 or INPP5 is fused to an N-terminal GPCR moiety. These GPCR-INPPs (GIs) thus resemble the GKs and this structural similarity points to a role in spatiotemporal distribution of PIs at distinct membranes. With the ongoing research on putative phospholipid-based transport of effectors that are essential for pathogenicity it is worth to investigate the in vivo functions of GIs. Moreover, since GPCRs are the main drug targets, GKs and GIs might have potential as oomicide targets.