The ROTUNDIFOLIA3 gene of Arabidopsis thalianaencodes a new member of the cytochrome P-450 family that is required for the regulated polar elongation of leaf cells

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Abstract
The polarized processes of cell elongation play a crucial role in morphogenesis of higher plants. We reported previously that therotundifolia3 (rot3) mutant of Arabidopsis has a defect in the polar elongation of leaf cells. In the present study, we isolated two additional alleles with mutations in the ROT3gene. The ROT3 gene was cloned by a T-DNA-tagging method and isolation of the gene was confirmed by a molecular analysis of threerot3 mutant alleles obtained from different mutagenesis. TheROT3 gene encodes a cytochrome P-450 (CYP90C1) with domains homologous to regions of steroid hydroxylases of animals and plants. Expression of the ROT3 gene was detected in all major plant organs. Especially, higher expression was detected in the tissues that had high activity of cell division. We confirmed that the ROT3gene controls polar elongation specifically in leaf cells by an analysis of three rot3 mutants obtained from different mutagenesis experiments. Our results imply that the ROT3protein 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.