Abstract
Symmetrical root tissue is formed by the cell-devisions occured regularly in the root meristem of Arabidopsis. tonsoku(tsk) and SS93 are the short root mutants with disorganized cell layers. These mutants exhibit structural abnormality of apical meristems, disturbed phyllotaxy and fasciation of stems also. TSK gene encodes a nuclear protein with unknown function. The homologous gene of tobacco cell culture BY-2 expressed cell cycle dependently. The gene product of SS93 is the homolog of MUS308 of Drosophila containing both helicase motifs and the polymerase domains of prokaryotic DNA polymerase. SS93 seedling showed the hypersensitivity to the DNA-damaging agents. Several abnormalities might be induced by the increase of double-strand break of chromosomal DNA were shown in SS93. These results and phenotypic similarity with fas1 and fas2 mutant indicate that the phenotypes of these mutants might be caused by the defect of DNA repair or cell cycle control.
