Chemotaxis and oospore formation in Phytophthora sojae are controlled by G‐protein‐coupled receptors with a phosphatidylinositol phosphate kinase domain

Abstract

SummaryG-protein-coupled receptors (GPCRs) are key cellular components that mediate extracellular signals into intracellular responses. Genome mining revealed that Phytophthora spp. have over 60 GPCR genes among which a prominent class of 12 encoding novel proteins with an N-terminal GPCR domain fused to a C-terminal phosphatidylinositol phosphate kinase (PIPK) domain. This study focuses on two GPCRPIPKs (GKs) in Phytophthora sojae. PsGK4 and PsGK5 are differentially expressed during the life cycle with the highest expression in cysts and during cyst germination, and at late infection stages. In P. sojae transformants that constitutively express RFP-tagged PsGK4 and PsGK5, the fusion proteins in hyphae reside in small, rapidly moving vesicular-like structures. Functional analysis using gene silencing showed that PsGK4-silenced transformants displayed higher levels of encystment and a reduced cyst germination rate when compared with the recipient strain. Moreover, GK4 deficiency (or reduction) resulted in severe defects in zoospore chemotaxis towards isoflavones and soybean roots. In contrast, PsGK5-silenced transformants exhibited no obvious defects in asexual development but oospore production was severely impaired. Both, PsGK4-and PsGK5-silenced transformants showed reduced pathogenicity. These results point to involvement of GKs in zoospore behaviour, chemotaxis and oospore development, and suggest that PsGK4 and PsGK5 each head independent signalling pathways.

Profiling the Secretome and Extracellular Proteome of the Potato Late Blight Pathogen Phytophthora infestans

“…The mechanism that triggers protein secretion in Phytophthora remains to be determined but, as reported for fungi, nutrient sensing G protein-coupled receptors (GPCRs) could play a crucial role in this process (57). Indeed, the Phytophthora genomes harbor around 60 genes encoding putative GPCRs, among which are novel classes that might be involved in direct downstream signaling and play roles in chemotaxis as well as in developmental aspects (58,59).…”

GK4, a G‐protein‐coupled receptor with a phosphatidylinositol phosphate kinase domain in Phytophthora infestans, is involved in sporangia development and virulence

“…Similar GK expression patterns were observed in P. sojae for which we extracted data from the P. sojae RNA‐seq transcriptional database presented by Ye et al . (Ye et al ., ; Yang et al ., , accompanying paper).…”

“…Transformants expressing full‐length mRFP fusion proteins (OX G4K4R 1, 2 and 3) showed significantly lower fluorescence intensity but their distribution matched the observations made for GPCR::mRFP fusion proteins. Similar to PiGK1 and PiGK4, PsGK5 in P. sojae does not localize to the plasma membrane but resides in fast moving vesicles that might be different from the ones that contain PiGK1 or PiGK4 (Yang et al ., , accompanying paper). In other organisms, GPCRs are primarily localized in plasma membranes although presence in intracellular organelles including ER, Golgi and endosomes has been reported (Marchese et al ., ; Toshima et al ., ; Hislop and von Zastrow, ).…”

“…In fact, this study and the accompanying paper by Yang et al . () demonstrate potentially distinct functions for Phytophthora GKs because the phenotypes of silenced transformants as well as their subcellular localization differ. GKs are also illustrative examples of oomycete‐specific proteins with novel domain combinations.…”

“…The phenotypic changes observed upon silencing and overexpression of GK genes in P. infestans in this study and in P. sojae by Yang et al . (, accompanying paper) imply that GKs are involved in various aspects of life cycle management. GPCRs are currently the most important and successful target proteins for drug development (Schlyer and Horuk, ; Xue et al ., ) highlighting oomycete GKs as interesting tools to support the search for new compounds that target aggressive oomycete plant pathogens such as Phytophthora .…”