Cloning and genomic characterization of tomato sterol methyl transferase 1 involved in sterol pathway

In vascular plants, at least three SMT isoforms are present to control the pattern of phytosterols. In the present study, we report the isolation of a full-length coding SMT1 cDNA from S. lycopersicum. The SMT1 transcript has an open reading frame of 1038 bp nucleotides and encodes a putative protein of 346 amino acids with theoretical pI of 5.10 and calculated molecular mass of 84.18 KDa. The comparative analysis and phylogenetic analysis showed that the SMT1 sequence was closely related to other sterol methyl transferases. The predicted protein sequence showed four substrate binding regions including regions I (Y81 to F91), III (Y192 to H199) and IV (K215 to W235) that are sterol binding sites and region II (L124 to F133) that is the AdoMet binding site. No transmembrane and hydrophobic domains were predicted in tomato SMT1 protein; this suggested that tomato sterol 24-C-methyltransferase cloned in this work belongs to SMT1 class that catalyses the first committed step of sterol biosynthesis.