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Title: EXPORTIN1 Genes are Essential for Development and Function of the Gametophytes in Arabidopsis thaliana

Author
item BLANVILLAIN, ROBERT - ARS-UCB PLNT GENE EXP CTR
item BOAVIDA, LEONOR - ARS-UCB PLNT GENE EXP CTR
item McCormick, Sheila
item Ow, David

Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2008
Publication Date: 9/14/2008
Citation: Blanvillain, R., Boavida, L., McCormick, S.M., Ow, D.W. 2008. EXPORTIN1 Genes are Essential for Development and Function of the Gametophytes in Arabidopsis thaliana. Genetics. 180(3):1493-1500. Epub 2008 Sep 14.

Interpretive Summary: Through studies on several nucleocytoplasmic proteins that enhance tolerance to metal and oxidative stresses, we found they relocate to the nucleus in the presence of leptomycin B, a specific inhibitor of exportin1 (XPO1). To verify the dependence of these proteins on XPO1-mediated nuclear export, we attempted to recover a mutant lacking XPO1. In Arabidopsis, there are two exportin1 genes. Single mutants appeared normal, so we concluded that each of the two genes could functionally mask the loss of the other. However a double mutant homozygote was not recovered. Distortions from expected segregation ratios indicated that the double mutant gametes are not viable. Co-transmission of mutant alleles was abolished through the female and strongly reduced through the male. Female gametophytes that were mutant at both genes showed defects ranging from early developmental arrests to disorganized cellular constitutions. Depending on the genotype of the maternal sporophyte, zygotes could be produced, but they did not develop into embryos. We concluded that a maternal copy of XPO1 is required for establishing a viable embryo.

Technical Abstract: 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.