Abstract
Sterols serve as both bulk membrane lipid components and precursors for steroid hormones. In higher plants, cytochrome P450s (CYP710A) catalyze the sterol C-22 desaturase reaction at the last step in the sterol biosynthetic pathway. Homology searches with Arabidopsis CYP710A1 protein sequence led to the identification of EST clones containing sequence stretches derived from two putative CYP710A genes (Pp710A13 and Pp710A14) in the moss, Physcomitrella patens. The deduced primary structures of Pp710A13 and Pp710A14 proteins were 81.2 % identical and contained the unique sequence, which conserved among the sterol C-22 desaturase P450 proteins so far reported, in the helix region distal to the 5th ligand of the heme. In Arabidopsis Pp710A overexpression lines, stigmasterol (Δ22-sterol) levels dramatically increased, and enzyme assays using recombinant Pp710A proteins confirmed these C-22 desaturase reactions in vitro. These results indicated that CYP710A family genes are widely conserved as the sterol C-22 desaturase in plant kingdom.
