RT Journal Article
SR Electronic
T1 Brassinosteroid-6-Oxidases from Arabidopsis and Tomato Catalyze Multiple C-6 Oxidations in Brassinosteroid Biosynthesis
JF Plant Physiology
JO Plant Physiol.
FD American Society of Plant Biologists
SP 770
OP 779
DO 10.1104/pp.126.2.770
VO 126
IS 2
A1 Shimada, Yukihisa
A1 Fujioka, Shozo
A1 Miyauchi, Narumasa
A1 Kushiro, Masayo
A1 Takatsuto, Suguru
A1 Nomura, Takahito
A1 Yokota, Takao
A1 Kamiya, Yuji
A1 Bishop, Gerard J.
A1 Yoshida, Shigeo
YR 2001
UL http://www.plantphysiol.org/content/126/2/770.abstract
AB Brassinosteroids (BRs) are steroidal plant hormones that are essential for growth and development. It has been proposed that BRs are synthesized via two parallel pathways, the early and late C-6 oxidation pathways according to the C-6 oxidation status. The tomato (Lycopersicon esculentum) Dwarf gene encodes a cytochrome P450 that has been shown to catalyze the C-6 oxidation of 6-deoxocastasterone to castasterone. We isolated an Arabidopsis ortholog (AtBR6ox gene) of the tomatoDwarf gene. The encoded polypeptide has characteristics of P450s and is classified into the CYP85 family. TheAtBR6ox and tomato Dwarf gene were expressed in yeast and the ability of the transformed yeast cells to metabolize 6-deoxo-BRs was tested. Metabolites were analyzed by gas chromatography-mass spectrometry. Both enzymes catalyze multiple steps in BR biosynthesis: 6-deoxoteasterone to teasterone, 3-dehydro-6-deoxoteasterone to 3-dehydroteasterone, 6-deoxotyphasterol to typhasterol, and 6-deoxocastasterone to castasterone. Our results indicate that the AtBR6ox gene and the tomatoDwarf gene encode steroid-6-oxidases and that these enzymes have a broad substrate specificity. This suggests that the BR biosynthetic pathway consists of a metabolic grid rather than two separate parallel pathways.