Molecular cloning and expression analysis of a leaf-specific expressing 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase gene from Michelia chapensis Dandy

The 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyzes the conversion of HMG-CoA to mevalonate, which is the first committed step in the pathway for isoprenoid biosynthesis in plants. In this research, a full-length cDNA encoding HMGR, designated as MichHMGR (GenBank Accession No. DQ098012) was isolated from Michelia chapensis Dandy by rapid amplification of cDNA ends (RACE). The full-length cDNA of MichHMGR comprised 2229 base pairs (bp) with a 1671 bp open reading frame (ORF) encoding a 556-amino-acid polypeptide that contained two trans-membrane domains. The deduced protein designated as MichHMGR had an isoelectric point (pI) of 8.34 and a calculated molecular weight of about 59.3 kDa. Sequence comparison analysis showed that MichHMGR had highest homology to HMGR from Morus alba . As expected, phylogenetic tree analysis indicated that MichHMGR belonged to plant HMGR group. Southern blot analysis showed that MichHMGR belonged to a small gene family. Tissue expression pattern analysis showed that MichHMGR was only expressed in the leaves whereas no expression was found in the stems and roots. Reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that MichHMGR expression could be induced by exogenous methyl jasmonate and salicylic acid. The functional color complementation assay indicated that MichHMGR could accelerate the biosynthesis of carotenoids in the Escherichia coli transformant, demonstrating that MichHMGR played an influential role in isoprenoid biosynthesis.