CHARACTERIZATION OF A POLLEN-EXPRESSED RECEPTOR-LIKE KINASE GENE OF PETUNIA-INFLATA AND THE ACTIVITY OF ITS ENCODED KINASE

From a pollen tube cDNA library of Petunia inflata, we isolated clones encoding a protein with structural features and biochemical propertie s characteristic of receptor-like kinases. It was designated PRK1 for pollen receptor-like kinase 1. The cytoplasmic domain of PRK1 is highl y similar to the kinase domains of other plant receptor-like kinases a nd contains nearly all of the conserved amino acids for serine/threoni ne kinases. The extracellular domain of PRK1 contains leucine-rich rep eats as found in some other plant receptor-like kinases, but overall i ts sequence in this region does not share significant similarity. Char acterization of a gene encoding PRK1 revealed the presence of two intr ons. During pollen development, PRK1 mRNA was first detected in anthem containing mostly binucleate microspores; it reached the highest leve l of mature pollen and remained at a high level in in vitro-germinated pollen tubes. The recombinant cytoplasmic domain of PRK1 autophosphor ylated on serine and tyrosine, suggesting that PRK1 may be a dual-spec ificity kinase. Monospecific immune serum to the recombinant extracell ular domain of PRK1 detected a 69-kD protein in microsomal membranes o f pollen and pollen tubes. The characteristics of PRK1 suggest that it may play a role in signal transduction events during pollen developme nt and/or pollination.