Abstract
Protein ubiquitination is important for the regulation of meiosis in eukaryotes, including plants. However, little is known about the involvement of E2 ubiquitin-conjugating enzymes in plant meiosis. Arabidopsis UBC22 is a unique E2 enzyme, able to catalyze the formation of ubiquitin dimers through lysine 11 (K11). Previous work has shown that ubc22 mutants are defective in megasporogenesis, with most ovules having no or abnormally functioning megaspores; furthermore, some mutant plants show distinct phenotypes in vegetative growth. In this study, we showed that chromosome segregation and callose deposition were abnormal in mutant female meiosis while male meiosis was not affected. The meiotic recombinase DMC1, required for homologous chromosome recombination, showed a dispersed distribution in mutant female meiocytes compared to the presence of strong foci in WT female meiocytes. Based on an analysis of F1 plants produced from crosses using a mutant as the female parent, about 24% of female mutant gametes had an abnormal content of DNA, resulting in frequent aneuploids among the mutant plants. These results show that UBC22 is critical for normal chromosome segregation in female meiosis but not for male meiosis, and they provide important leads for studying the role of UBC22 and K11-linked ubiquitination.
Highlights
Meiosis is a modified cell cycle with one round of DNA replication and two rounds of cell division, producing haploid gametes from diploid somatic cells
To investigate the effect of UBC22 inactivation on megasporogenesis, we used callose as a marker with which to examine female meiosis
A polysaccharide composed of glucose residues linked through β-1,3-linkages, is present at the cell plate during meiosis prior to cytokinesis, and has been used as a convenient cytological marker for meiosis in megaspore mother cells (MMCs or female meiocytes) [46]
Summary
Meiosis is a modified cell cycle with one round of DNA replication and two rounds of cell division, producing haploid gametes from diploid somatic cells. The SC is a highly conserved structure formed in prophase I along the length of homologous chromosomes. It consists of a pair of parallel strands, called lateral elements, with the loops of sister chromatids attached, and the lateral elements are linked by a central element [2]. The inactivation of Arabidopsis ASY1 or ASY3 results in the failure of synapsis and a disruption in the formation of the SC [7,8] These results show that the two plant axial proteins play an important role in the pairing and synapsis of homologous chromosomes
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