Exportin1 genes are essential for development and function of the gametophytes in Arabidopsis thaliana

Gametes are produced in plants through mitotic divisions in the haploid gametophytes. We investigated the role of EXPORTIN1 (XPO1) genes during the development of both female and male gametophytes of Arabidopsis. Exportins exclude target proteins from the nucleus and are also part of a complex recruited at the kinetochores during mitosis. Here we show that double mutants in Arabidopsis XPO1A and XPO1B are gametophytic defective. In homozygous-heterozygous plants, 50% of the ovules were arrested at different stages according to the parental genotype. Double-mutant female gametophytes of xpo1a-3/+; xpo1b-1/xpo1b-1 plants failed to undergo all the mitotic divisions or failed to complete embryo sac maturation. Double-mutant female gametophytes of xpo1a-3/xpo1a-3; xpo1b-1/+ plants had normal mitotic divisions and fertilization occurred; in most of these embryo sacs the endosperm started to divide but an embryo failed to develop. Distortions in male transmission correlated with the occurrence of smaller pollen grains, poor pollen germination, and shorter pollen tubes. Our results show that mitotic divisions are possible without XPO1 during the haploid phase, but that XPO1 is crucial for the maternal-to-embryonic transition.