title: The Arabidopsis gene tardy asynchronous meiosis is required for the normal pace and synchrony of cell division during male meiosis.
abstract: Male meiosis in higher organisms features synchronous cell divisions in a large number of cells. It is not clear how this synchrony is achieved, nor is it known whether the synchrony is linked to the regulation of cell cycle progression. Here, we describe an Arabidopsis mutant, named tardy asynchronous meiosis (tam), that exhibits a phenotype of delayed and asynchronous cell divisions during male meiosis. In Arabidopsis, two nuclear divisions occur before simultaneous cytokinesis yields a tetrad of haploid cells. In tam, cell divisions are delayed, resulting in the formation of abnormal intermediates, most frequently dyad meiotic products, or in rare cases, dyad pollen (two gametophytes within one exine wall). Temperature-shift experiments showed that the percentage of the abnormal intermediates increased at 27 degrees C. Analysis of tam and the tam/quartet1 double mutant showed that most of these abnormal intermediates could continue through the normal rounds of cell divisions and form functional pollen, though at a slower than normal pace. The asynchrony of cell division started at the G2/M transition, with cells entering metaphase at different time points, during both meiosis I and II. In addition, chromosome condensation defects and mis-segregation were sometimes observed in tam. These observations suggest that the TAM protein positively regulates cell cycle progression, perhaps by promoting the G2/M transition. We speculate that there is a signal, perhaps TAM, that couples the normal pace of cell cycle progression with the synchrony of cell division during male meiosis.
authors.affiliation: Plant Gene Expression Center, United States Department of Agriculture/Agricultural Research Service, University of California, 800 Buchanan Street, Albany, CA 94710, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Magnard
authors.forename: M
authors.initials: M
authors.lastname: Yang
authors.forename: Y C
authors.initials: YC
authors.lastname: Chen
authors.forename: M
authors.initials: M
authors.lastname: Leary
authors.forename: S
authors.initials: S
authors.lastname: McCormick
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D002455:Cell Division; D002874:Chromosome Mapping; D015638:Cytochalasin D / Q000494:pharmacology; D006358:Hot Temperature; D008540:Meiosis / Q000187:drug effects / Q000235:genetics*; D016296:Mutagenesis; D010641:Phenotype; D011058:Pollen / Q000235:genetics / Q000254:growth & development; D012098:Reproduction; D012737:Sex Factors; D015398:Signal Transduction
chemical_list: D015638:Cytochalasin D