THE ROTUNDIFOLIA3 GENE OF ARABIDOPSIS-THALIANA ENCODES A NEW MEMBER OF THE CYTOCHROME-P-450 FAMILY THAT IS REQUIRED FOR THE REGULATED POLARELONGATION OF LEAF-CELLS

The polarized processes of cell elongation play a crucial role in morp hogenesis of higher plants. We reported previously that the rotundifol ia3 (rot3) mutant of Arabidopsis has a defect in the polar elongation of leaf cells. In the present study, we isolated two additional allele s With mutations in the ROT3 gene. The ROT3 gene was cloned by a T-DNA -tagging method and isolation of the gene was confirmed by a molecular analysis of three rot3 mutant alleles obtained from different mutagen esis. The ROT3 gene encodes a cytochrome P-450 (CYP90Cl) with domains homologous to regions of steroid hydroxylases of animals and plants. E xpression of the ROT3 gene was detected in all major plant organs. Esp ecially, higher expression was detected in the tissues that had high a ctivity of cell division. We confirmed that the ROT3 gene controls pol ar elongation specifically in leaf cells by an analysis of three rot3 mutants obtained from different mutagenesis experiments. Our results i mply that the ROT3 protein is a member of a new class of cytochrome P- 450 encoding putative steroid hydroxylases, which is required for the regulated polar elongation of cells in leaves of Arabidopsis.