Translocation of phospholipase A(2)alpha to apoplasts is modulated by developmental stages and bacterial infection in Arabidopsis

Phospholipase A(2) (PLA(2)) hydrolyzes phospholipids at the sn-2 position to yield lysophospholipids and free fatty acids. Of the four paralogs expressed in Arabidopsis, the cellular functions of PLA(2)alpha in planta are poorly understood. The present study shows that PLA(2)alpha possesses unique characteristics in terms of spatiotemporal subcellular localization, as compared with the other paralogs that remain in the ER and/or Golgi apparatus during secretory processes. Only PLA(2)alpha is secreted out to extracellular spaces, and its secretion to apoplasts is modulated according to the developmental stages of plant tissues. Observation of PLA(2)alpha-RFP transgenic plants suggests that PLA(2)alpha localizes mostly at the Golgi bodies in actively growing leaf tissues, but is gradually translocated to apoplasts as the leaves become mature. When Pseudomonas syringae pv. tomato DC3000 carrying the avirulent factor ayrRpm1 infects the apoplasts of host plants, PLA(2)alpha rapidly translocates to the apoplasts where bacteria attempt to become established. PLA2 alpha promoter::GUS assays show that PLA(2)alpha gene expression is controlled in a developmental stage- and tissue-specific manner. It would be interesting to investigate if PLA(2)alpha functions in plant defense responses at apoplasts where secreted PLA(2)alpha confronts with invading pathogens.