Plant sterol-C24-methyl transferases: Different profiles of tobacco transformed with SMT1 or SMT2

Higher plant cells contain a mixture of 24-desmethyl, 24-methyl(ene), and 2 4-ethyl(idene) sterols in given proportions according to species but also t o cell type. As a first step to investigate the function of such sterol com positions in the physiology of a plant, we have illustrated in the present work the coexistence of two distinct (S)-adenosyl-L-methionine sterol-C24-m ethyltransferases (SMT) in transgenic Nicotiana tabacum L. Indeed, modulati on of the expression of the tobacco gene SMT1-1, which encodes a cycloarten ol-C24-methyltransferase, results in variations of the proportion of cycloa rtenol and a concomitant effect on the proportion of 24-ethyl sterols. Over expression in tobacco of the Arabidopsis thaliana (L.) Heynh. gene SMT2-1 w hich encodes a 24-methylene lophenol-C24(1)-methyltransferase, results in a dramatic modification of the ratio of 24-methyl cholesterol to sitosterol associated with a reduced growth, a topic discussed in the present work.