Poster: Lipids & related molecules

Abs # 309: Physiological ramification of atypical steroid accumulation in transgenic tobacco expressing a 3-hydroxysteroid oxidase gene in the chloroplast.

Presenter:	Ruffino, John , RuffinoJ@canisius.edu
Authors	Ruffino, John  (A)   Fordyce, Amber  (A)   DeWitt, Matt  (A)   Heyer, Jannelle  (A)   Parker, Brandon  (A)   Becker, David  (B)   Grebenok, Robert  (A)
Affiliations:	(A): Canisius College, Department of Biology (B): Pomona College, Department of Biology

The requirement for sterols in higher plant membranes has been well established, but specific sterol levels required for physiological function remain undetermined. Neither is it clear if specific ratios of sterols are required for successful growth and reproduction of higher plants. In transgenic plants expressing a 3-hydroxysteroid oxidase in the chloroplast, a portion of the sterol pool, including sitosterol, stigmasterol, campesterol and cholesterol is converted to a 3-ketosteroid metabolite, which upon reduction by endogenous enzymes, culminates in stanol accumulation. Plants maintaining sterol titers reduced by 77% as a result of 3-hydroxysteroid oxidase action exhibit no morphological abnormalities of consequence. However, campestanol and campestan-3-one account for 100% of the measurable methylated steroid in the transgenic plants examined, while sitosterol is represented entirely by sitostanol and sitostan-3-one. We report ratios of steroids maintaining specific side chain chemistries for control and transgenic plant organs. The sterol ratios are grossly altered in the transgenic plants, where ethylated side chain sterols compose 99% of the total sterol pool. However, in transgenic plants, the sums of sterol, the respective 3-ketosteroid and stanol, provide relative ratios of total steroid maintaining particular side chain chemistries, which are similar to controls. The modified sterol budget correlates with capacity for two-fold higher rates of electron transport in transgenic plant chloroplasts. The relationship between 3-hydroxysteroid oxidase localization, steroid accumulation pattern and plant ontogeny is discussed.