Abstract
A-type cyclin-dependent kinase (CDKA), a homolog of cdc2, has a role throughout the cell cycle in plants. Here we show that a loss-of-function mutation in Arabidopsis CDKA;1 results in male gametophyte lethality. Heterozygous plants produced mature siliques containing ca. 50% aborted seeds, and segregation distortion was observed in paternal inheritance. Microspores normally undergo pollen mitosis I (PMI), and the resulting smaller generative cell undergoes second mitosis, PMII, to form two sperm cells. The cdka-1 mutant, however, produces pollen grains, consisting of a single sperm-like cell. The mutant sperm-like cell is fertile, and preferentially fuses with the egg cell to initiate embryogenesis. As the central cell nucleus remains unfertilized, however, double fertilization does not occur. In heterozygous plants, the embryo is arrested at the globular stage, most likely because of loss of normal endosperm development. Thus, CDKA;1 is essential for cell division of the generative cell in male gametogenesis.
