TPR5 is involved in directional cell division and is essential for the maintenance of meristem cell organization in Arabidopsis thaliana

Root growth in plants is achieved through the co-ordination of cell division and expansion. In higher plants, the radial structure of the roots is formed during embryogenesis and maintained thereafter throughout development. Here we show that the tetratricopeptide repeat domain protein TPR5 is necessary for maintaining radial structure and growth rates in Arabidopsis thaliana roots. We isolated an A. thaliana mutant with reduced root growth and determined that TPR5 was the gene responsible for the phenotype. The root growth rate of the tpr5-1 mutant was reduced to ~60% of that in wild-type plants. The radial structure was disturbed by the occurrence of occasional extra periclinal cell divisions. While the number of meristematic cells was reduced in the tpr5 mutants, the cell length in the mature portion of the root did not differ from that of the wild type, suggesting that TPR5 is required for proper cell division but dispensable for cell elongation. Expression of the TPR5–GFP fusion protein driven by the TPR5 promoter displayed fluorescence in the cytoplasm of root meristems, but not in mature root regions. DNA staining revealed that frequencies of micronuclei were increased in root meristems of tpr5 mutants. From this study, we concluded that TPR5 is involved in preventing the formation of micronuclei and is necessary for both the activity and directionality of cell division in root meristems.