POLLEN-TUBE LOCALIZATION IMPLIES A ROLE IN POLLEN-PISTIL INTERACTIONSFOR THE TOMATO RECEPTOR-LIKE PROTEIN-KINASES LEPRK1 AND LEPRK2

We screened for pollen-specific kinase genes, which are potential sign al transduction components of pollen-pistil interactions, and isolated two structurally related receptor-like kinases (RLKs) from tomato, Le PRK1 and LePRK2. These kinases are similar to a pollen-expressed RLK f rom petunia, but they are expressed later during pollen development th an is the petunia RLK. The abundance of LePRK2 increases when pollen g erminates, but LePRK1 remains constant. Both LePRK1 and LePRK2 are loc alized to the plasma membrane/cell wall of growing pollen tubes. Both kinase domains have kinase activity when expressed in Escherichia coli , In phosphorylation assays with pollen membrane preparations, LePRK2, but not LePRK1, is phosphorylated, and the addition of tomato style, but not leaf, extracts to these membrane preparations results at least partially in specific dephosphorylation of LePRK2. Taken together, th ese results suggest that LePRK1 and LePRK2 play different roles in pos tpollination events and that at least LePRK2 may mediate some pistil r esponse.