Arabidopsis TSO1 regulates directional processes in cells during floral organogenesis

Flowers of the previously described Arabidopsis tso1-1 mutant had aberrant, highly reduced organs in place of petals, stamens, and carpels. Cells of tso1-1 flowers had division defects, including failure in cytokinesis, partial cell wall formation, and elevated nuclear DNA content. We describe here two new tso1 alleles (tso1-3 and tso1-4), which caused defects in ovule development, but had little effect on gross floral morphology. Early ovule development occurred normally in tso1-3 and tso1-4, but the shapes and alignments of integument cells became increasingly more disordered as development progressed. tso1-3 ovules usually lacked embryo sacs due to a failure to form megaspore mother cells. The cell division defects described for the strong tso1-1 mutant were rarely observed in tso1-3 ovules. The aberrations in tso1-3 mutants primarily resulted from a failure in directional expansion of cells and/or coordination of this process among adjacent cells. Effects of tso1-3 appeared to be independent of effects of other ovule development mutations, with the exception of leunig, which exhibited a synergistic interaction. The data are consistent with TSO1 acting in processes governing directional movement of cellular components, indicating a likely role for TSO1 in cytoskeletal function.