The protein kinase genes MAP3Ke1 and MAP3Ke2 are required for pollen viability in Arabidopsis thaliana

We have used reverse-genetic analysis to investigate the function of MAP3Ke1 and MAP3Ke2, a pair of closely related Arabidopsis thaliana genes that encode protein kinases. Plants homozygous for either map3ke1 or map3ke2 displayed no apparent mutant phenotype, whereas the double-mutant combination caused pollen lethality. Transmission of the double-mutant combination through the female gametophyte was normal. Tetrad analysis performed using the Arabidopsis quartet mutation demonstrated that the pollen-lethal phenotype segregated at meiosis with the map3ke1;map3ke2 genotype. We used transmission electron microscopy to determine that double-mutant pollen grains develop plasma embrane irregularities following pollen mitosis I. Analysis of the subcellular localization of a yellow fluorescent protein (YFP):MAP3Ke1 fusion protein using confocal microscopy and biochemical fractionation indicated that a substantial portion of the MAP3Ke1 present in Arabidopsis cells is localized to the plasma membrane. Taken together, our results suggest that MAP3Ke1 is required for the normal functioning of the plasma membrane in developing Arabidopsis pollen.