Molecular and genetic characterization of transgenic tomato expressing 3-hydroxy-3-methylglutaryl coenzyme A reductase

Mevalonic acid (MVA) pathway, in parallel with methylerythritol phosphate (MEP) pathway, produces precursor metabolites for isoprenoids, and affect fruit development in plants. 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is supposed to be a key enzyme in the MVA pathway. To understand the role of HMGR in fruit development, we previously generated transgenic tomato (Solanum lycopersicum) expressing a melon HMGR gene (CmHMGR) and observed increased fruit size in these plants. To further examine this effect, we performed molecular and genetic characterization of the transgenic tomato line in the T-4 generation. The line showed stable expression of CmHMGR mRNA and protein, an effect that could lead to the increase in fruit weight observed, which exceeded 20%. Interestingly, the CmHMGR mRNA was highly expressed during tomato fruit development, whereas expression of the endogenous HMGRs (SlHMGR1, SlHMGR2, and SlHMGR3) was lower than in the wild type, suggesting the presence of a regulatory mechanism at the transcriptional level, as in mammalian systems. A preliminary analysis using cDNA macroarray filters was performed, and genes showing more than 2.5-fold differences in expression between transgenic and wild-type plants were identified. Most of the genes involved in isoprenoid biosynthesis did not show significantly different transcription levels, but 121 annotated genes and 152 genes of unknown function were found to be differentially expressed. These results demonstrate that the transgenic tomato line expressing the HMGR gene is genetically stable and could be used as a comprehensive material to elucidate the roles of HMGRs in tomato fruit development.