THE STUD GENE IS REQUIRED FOR MALE-SPECIFIC CYTOKINESIS AFTER TELOPHASE-II OF MEIOSIS IN ARABIDOPSIS-THALIANA

During male meiosis in wild-type Arabidopsis the pollen mother cell (P MC) undergoes two meiotic nuclear divisions in the absence of cell div ision. Only after telophase II is a wall formed which partitions the P MC into four microspores. Each microspore undergoes two subsequent mit otic divisions to produce one vegetative cell and two sperm cells in t he mature pollen grain. In this paper we describe the isolation and th e phenotypic characterization of mutations in the STUD (STD) gene, whi ch is specifically required for male-specific cytokinesis after teloph ase II of meiosis. Although the male meiotic nuclear divisions are nor mal in std mutant plants, no walls are formed resulting in a tetranucl eate microspore. Despite the absence of cell division in the PMC, post meiotic development in the coenocytic microspore proceeds relatively n ormally, resulting in the formation of large pollen grains which conta in four vegetative nuclei and up to eight sperm cells. Interestingly, these enlarged pollen, grains which contain multiple vegetative nuclei and extra sperm cells behave as single male gametophytes, producing o nly single pollen tubes and resulting in partial male fertility in std mutant plants. Characterization of the process of pollen development and pollen function in std mutants thus reveals two different types of developmental regulation. Each of the four nuclei found in a std micr ospore following meiosis is capable of independently undergoing the co mplete mitotic cell division (including cytokinesis) which the single nucleus of a wild type microspore would normally undertake. The abilit y of the four meiotic products to independently continue through mitos is does not depend on their division into separate cells, but is contr olled by some subcellular component found within the coenocytic microp sore. By contrast, the mature std pollen grain functions as a unit and produces only a single pollen tube despite the presence of multiple n uclei within the vegetative cell, suggesting that this process is cont rolled at the cellular level independently of the extra subcellular co mponents. (C) 1997 Academic Press.