(The) role of MOS7, a nucleoporin88 homolog, in the development of Arabidopsis gametophytes

Abstract

Unlike animals, plants have alternation of generation during reproduction, a diploid sporophytic and a haploid gametophytic generation. Both the female and male gametophytes are created by meiosis followed by subsequent haploid mitoses. For more than a decade, a number of genes have been isolated that are expressed during reproductive stage including gametophyte, zygotic embryo and endosperm development. Nevertheless, the details of how these relevant genes interact in the reproductive stage are still poorly characterized. Therefore, I have studied a molecular regulatory mechanism to the understanding of gametophytic and seed development in Arabidopsis thaliana. In this study, the mos7-5 mutant was isolated based on an abortion phenotype during reproductive stage. MOS7 (Modifier Of Snc1,7) encodes a nucleoporin88 (Nup88) homolog in Arabidopsis. MOS7/mos7-5 mutant is a recessive loss-of-function mutant and no homozygous mutants were obtained. Megagametogenesis did not proceed beyond the FG2 stage in 48% of the mos7-5 heterozygous mutants. The development of embryo sacs was impaired. Similarly, mitotic defects during microgametogenesis were also observed. The mos7-5 allele is haplo-insufficient in sporocytes, resulting in delayed cell arrest during the mitotic division after meiosis completion. After fertilization, about 14% of the seeds were aborted. These aborting seeds were mos7-5 homozygous which were verified by quantitative PCR. Yeast two hybrid screen identified dynein light chain type 1 family protein and kinectin-related protein, as MOS7-interacting proteins, which were further confirmed by BiFC analysis in planta. Furthermore, interactions between MOS7 and several nucleoporin known to control spindle dynamics, Rae1 and Nup98, were detected. Microtubule-reporter analysis revealed that MOS7 localize at the mitotic spindle structure during mitosis in proliferating cells. Overall microtubule dynamics including spindle assembly, spindle attachment to the kinetochore and phragmoplast formation were defective in MOS7/mos7-5 heterozygous mutants during gametogenesis. These results demonstrate that MOS7 is required for proper microtubule dynamics through interaction with Rae1 and Nup98a or with dynein light chain and kinectin-related proteins during cell divisions. Conclusions made in the developing both gametogenesis can be extrapolated to somatic cells in that microtubule-organizing spindle and phragmoplast formation is the fundamental basis of plant cell growth. Taken together, MOS7 have a critical role in microtubule organization during mitosis in Arabidopsis thaliana.