Cloning and sequence analysis of HMG-CoA reductase full-length cDNA from tea (Camellia sinensis).

Aroma is an important character of tea, and terpenoids, with preferable fragrance and relatively high boiling point , are substantial substances contributing to tea aroma, which not only determine the aroma quality of tea, but also provide a classification basis of scent types. In plants, sesquiterpenes and dolichol and so forth are synthesize via the cytoplasmic mevalonate-dependent pathway. The enzyme HMG-CoA reductase (HMGR) catalyzes the conversion of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) to mevalonate, which is the committed step in the synthesis of isoprenoids via the MVA pathway. To help understand the molecular and genetic mechanisms underlying terpenoid synthesis of tea, a full-length cDNA encoding HMGR was cloned from tea (Cainellia sinensis (L.) O. Kuntze) by using the RACE-PCR technique (designated as CsHMGR 1). It comprised 1 979 bp, with a 1 722 bp intact open reading frame encoding a 573-amino-acid protein. The deduced protein showed 80% to 82% similarities to homologs from rubber tree (Hevea brasiliensis) , common camptotheca fruit (sam ptotheca acum mate) , ginseng (Panax ginseng), litchis (Litchi chinensis) ,American ginseng (Panax qumnquefolius) ,rooted salvia (Salvia miltiorrhiza) , Momordica grosvenori (Siraitia grosvenorii) , and longan (Dimocarpus ion gan). The phylogenetic tree, constructed with the cat- alytic domained of CsHMGR1 and homologs from other species, indicated that CsHMGR1 belonged to the eukaryotic class I HMGR family. CsHMGR1 consisted of two transmembrane domains, implying that it may be localized to en- doplasmic reticulum (ER) similarly to other eukaryotic homologs. It also contained two HMG-CoA binding sites, two NADP( H) -binding sites, four conserved catalytic active residues and a phosphorylation site, indicating that phospho- rylation/dephosphorylation is likely a crucial mode of regulation of its biochemical activity. Tissue expression analysis indicated that CsHMGR1 was expressed comparatively in the leaf buds of C. sinensis cv. Dayelong and in both leaf buds and floral buds of the mother plants. The regulation of expression and physiological activity of CsHMGR1 are likely to impact greatly on tea quality, and CsHMGR1 may provide a basis of the quality evaluation and breeding of tea given that its function is further resolved. [ABSTRACT FROM AUTHOR]