IDENTIFICATION BY PCR OF RECEPTOR-LIKE PROTEIN-KINASES FROM ARABIDOPSIS FLOWERS

We have isolated three receptor-like kinase cDNAs from an Arabidopsis flower cDNA library by PCR using degenerate oligonucleotide primers fo r conserved domains of protein kinases. Cloning and sequencing of the full-length cDNAs, designated RKF1 to 3 (receptor-like kinase in flowe rs), showed that the putative extracellular domain of the RKF1 protein contains 13 tandem repeats of leucine-rich sequences and those of RKF 2 and RKF3 have no significant homology with other plant sequences. RN A blot analysis revealed that the RKF1 mRNA is highly expressed in sta mens while RKF2 and RKF3 mRNAs are present at low levels in all organs examined. In situ localization experiments indicated that the RKF1 mR NA is detectable in early flower primordia and during stamen developme nt. In addition, when fused to a GUS reporter gene, the RKF1 promoter directed high GUS expression in pollen grains. Recombinant RKF1, produ ced in Escherichia coli, was found to have kinase activity with serine /threonine specificity in vitro.