Detection of Endogenous Phosphatidylinositol 4,5–bisphosphate in Phytophthora cinnamomi

Plant diseases caused by Phytophthora species are serious threats to agriculture and the natural environment. Genome sequencing has revealed the lack of a gene for canonical phospholipase C (PLC), an enzyme that was hitherto thought to be ubiquitous in eukaryotes. PLC acts in the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5-P2 ), a membrane-bound phospholipid critical for signal initiation in many cellular processes. Previous studies have not provided evidence of endogenous PtdIns-4,5-P2 in Phytophthora and, in the absence of canonical PLC, argued for redundancy or loss in the PLC pathway in Phytophthora. Using liquid chromatography mass spectrometry, we have detected endogenous PtdIns-4,5-P2 in Phytophthora cinnamomi. This is the first identification of the phospholipid in the genus, and is significant because it indicates that the signal transduction pathway of the PLC product, inositol 1,4,5-trisphosphate (IP3 ), may have been retained in Phytophthora incorporating an as-yet unidentified homolog or analog of PLC.