The protein kinase genes MAP3Kε1 and MAP3Kε2 are required for pollen viability in Arabidopsis thaliana

We have used reverse-genetic analysis to investigate the function of MAP3K epsilon 1 and MAP3K epsilon 2, a pair of closely related Arabidopsis thaliana genes that encode protein kinases. Plants homozygous for either map3k epsilon 1 or map3k epsilon 2 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 map3k epsilon 1;map3k epsilon 2 genotype. We used transmission electron microscopy to determine that double-mutant pollen grains develop plasma membrane irregularities following pollen mitosis I. Analysis of the subcellular localization of a yellow fluorescent protein (YFP):MAP3K epsilon 1 fusion protein using confocal microscopy and biochemical fractionation indicated that a substantial portion of the MAP3K epsilon 1 present in Arabidopsis cells is localized to the plasma membrane. Taken together, our results suggest that MAP3K epsilon 1 is required for the normal functioning of the plasma membrane in developing Arabidopsis pollen.