Abstract
The characterization of genes encoding sterol biosynthetic enzymes and the isolation of novel plant lines affected in the expression of those genes have shed new light on the involvement sterols may have in biological processes such as embryonic development, cell and plant growth, and fertility. Arabidopsis or N. benthamiana lines affected in the biosynthetic segment leading from cycloartenol to Δ7-sterol intermediates display severe phenotypes such as seedling lethality. Genetic lesions occuring between Δ7-intermediates and the final products campesterol and sitosterol result in dwarfism which is rescued by exogenous supply of brassinosteroids. The ratio of campesterol to sitosterol is regulated by the expression of sterol methyltransferases and particularly a 24-methylene lophenol-C24-methyltransferase. This ratio modulates Arabidopsis morphology and development. Interestingly, certain organs or cell types are more sensitive than others to variations of this ratio. Regulatory components involved in the expression of these biosynthetic genes remain to be disclosed.
