LYSIS OF PHOSPHOLIPASE C PAHTWAY IN THE INDUCTION OF DEFENSE RESPONSES TRIGGERED BY PHOSPHATIDYL INOSITOL 4-PHOSPHATE

GONORAZKY, A. G.; LAXALT, A.M.; DE LA CANAL, L

Rosario

Congreso; SAFV; 2008

SAFV

Various phosphoinositides have been implicated in plant signaling. Phosphatidylinositol 4-phosphate (PI4P) plays a role as precursor of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. Both, PI4P and PI(4,5)P2, are substrates of phospholipase C (PLC) that lead to the production of inositol 1,4-biphosphate (IP2) or inositol 1,4,5-triphosphate (IP3), respectively, and diacylglycerol (DAG). The later is subsequently phosphorylated by DAG kinase (DGK) to produce the second messenger phosphatidic acid (PA). Recently we have demonstrated that PI4P is accumulated in the extracellular medium of xylanase-elicited tomato cells, which suggests a putative role of extracellular PI4P as an intercellular signaling molecule (Gonorazky et al 2008). We have also shown that addition of PI4P to tomato cell suspensions mimics xylanase effects by inducing oxidative burst, increased levels of defense genes and cell death. Here we analyzed whether extracellular PI4P would play a role as a defence response-inductor per se, or if it would act as a substrate to produce other phospholipid-derived molecules. As a first approach, we incubated tomato cell suspensions with in vivo labelled 32PIP, wherein PI4P represents 80% of the PIP pool. We detected that exogenous 32PIP was incorporated by tomato cells within 15 minutes, increasing its level throughout 1 hour of incubation. In addition, 32PIP was partially converted to 32PI but not to 32PIP2. We studied as well whether PI4P could be a substrate of the PLC/DGK pathway. PI4P treatment of tomato cells did not induce an increase in PA derived from PLC/DGK activity. Nevertheless, treatment of tomato cells with PLC inhibitor U73122 diminished oxidative burst induced by applied PI4P. This data suggests that extracellular PI4P triggers the production of PLC-derived signalling molecules different from PA. It remains to be demonstrated whether applied PI4P plays a role as a PLC-inductor, or if it acts as a PLC-substrate which is converted into IP2 and DAG.