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Cytochrome P450 CYP710A encodes the sterol C-22 desaturase in Arabidopsis and tomato.

Morikawa T., Mizutani M., Aoki N., Watanabe B., Saga H., Saito S., Oikawa A., Suzuki H., Sakurai N., Shibata D., Wadano A., Sakata K., Ohta D.

Delta22-unsaturated sterols, containing a double bond at the C-22 position in the side chain, occur specifically in fungi and plants. Here, we describe the identification and characterization of cytochrome P450s belonging to the CYP710A family as the plant C-22 desaturase. Recombinant proteins of CYP710A1 and CYP710A2 from Arabidopsis thaliana and CYP710A11 from tomato (Lycopersicon esculentum) were expressed using a baculovirus/insect system. The Arabidopsis CYP710A1 and tomato CYP710A11 proteins exhibited C-22 desaturase activity with beta-sitosterol to produce stigmasterol (CYP710A1, K(m) = 1.0 microM and kinetic constant [k(cat)] = 0.53 min(-1); CYP710A11, K(m) = 3.7 microM and k(cat) = 10 min(-1)). In Arabidopsis transgenic lines with CYP710A1 and CYP710A11 overexpression, stigmasterol levels increased by 6-to 32-fold. Arabidopsis CYP710A2 was able to produce brassicasterol and stigmasterol from 24-epi-campesterol and beta-sitosterol, respectively. Sterol profiling analyses for CYP710A2 overexpression and a T-DNA insertion event into CYP710A2 clearly demonstrated in planta that CYP710A2 was responsible for both brassicasterol and stigmasterol production. Semiquantitative PCR analyses and promoter:beta-glucuronidase transgenic approaches indicated strict tissue/organ-specific regulation for each CYP710A gene, implicating differential tissue distributions of the Delta(22)-unsaturated sterols in Arabidopsis. Our results support the possibility that the CYP710 family may encode P450s of sterol C-22 desaturases in different organisms.

Plant Cell 18:1008-1022(2006) [PubMed] [Europe PMC]

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