TSO1 is a novel protein that modulates cytokinesis and cell expansion in Arabidopsis

Previous analyses of tso1 mutants revealed a loss of control of directional cellular expansion and coordination of growth of adjacent cells, and defec ts in karyokinesis and cytokinesis. We isolated TSO1 using a map-based appr oach, and show that it is a member of a family of at least three genes in A rabidopsis, Consistent with the mutant phenotype, TSO1 transcript was most abundant in flowers, where it accumulated to the highest levels in developi ng ovules and microspores, The putative TSO1 protein has two cysteine-rich regions that are similar to the CXC domains of a variety of proteins from p lants and animals, including a class of kinesins involved in chromosome seg regation, and enhancer of zeste-type proteins. Visualization of TSO1-fusion proteins indicated that TSO1 is a nuclear protein. The tso1 mutant phenoty pes and the novelty of the TSO1 sequence suggest the existence of previousl y unknown participants in regulation of directional processes in eukaryotic cells.