TSO1 functions in cell division during Arabidopsis flower development. Liu Z,Running M P,Meyerowitz E M Development (Cambridge, England) We describe an Arabidopsis mutant, tso1, which develops callus-like tissues in place of floral organs. The tso1 floral meristem lacks properly organized three cell layers, and the nuclei of these cells are irregular in size and shape. Further analyses reveal partially formed cell walls and increased DNA ploidy in tso1 floral meristem cells, indicating defects in mitosis and cytokinesis. Our finding that TSO1 is required for organ formation in floral tissues but not in other tissues indicates that TSO1 may encode a floral-specific cell division component, or that TSO1 function is redundant in nonfloral tissues. 10.1242/dev.124.3.665

Regulation of meristem organization and cell division by TSO1, an Arabidopsis gene with cysteine-rich repeats. Song J Y,Leung T,Ehler L K,Wang C,Liu Z Development (Cambridge, England) In higher plants, meristem organization and cell division regulation are two fundamentally important and intimately related biological processes. Identifying and isolating regulatory genes in these processes is essential for understanding higher plant growth and development. We describe the molecular isolation and analyses of an Arabidopsis gene, TSO1, which regulates both of these processes. We previously showed that tso1 mutants displayed defects in cell division of floral meristem cells including partially formed cell walls, increased DNA content, and multinucleated cells (Liu, Z., Running, M. P. and Meyerowitz, E. M. (1997). Development 124, 665-672). Here, we characterize a second defect of tso1 in influorescence meristem development and show that the enlarged influorescence in tso1 mutants results from repeated division of one inflorescence meristem into two or more influorescence meristems. Using a map-based approach, we isolated the TSO1 gene and found that TSO1 encodes a protein with cysteine-rich repeats bearing similarity to Drosophila Enhancer of zeste and its plant homologs. In situ TSO1 mRNA expression pattern and the nuclear localization of TSO1-GFP are consistent with a regulatory role of TSO1 in floral meristem cell division and in influorescence meristem organization. 10.1242/dev.127.10.2207