Cloning and characterization of the gene encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase in melon (Cucumis melo L. reticulatus)

We have isolated a cDNA for Cm-HMGR, encoding 3-hydroxy-3-methylglutaryl co enzyme A (HMG-CoA) reductase in melon (Cucumis melo L. reticulatus: Genbank Accession No. AB021862). Cm-HMGR encodes a polypeptide of 588 amino acids that contains two transmembrane domains and a catalytic domain. Database se arches revealed that Cm-HMGR shows homology to HMG1 (63.7%) and HMG2 (70.3% ) of tomato, to HMG1 (77.2%) and HMG2 (69.4%) of Arabidopsis thaliana, and to HMGR of tobacco (72.6%). Functional expression in a HMG-CoA reductase-de ficient mutant yeast showed that Cm-HMGR products mediate the synthesis of mevalonate. Northern analysis revealed that the level of Cm-HMGR mRNA in th e fruit increased after pollination and markedly decreased at the end of fr uit enlargement. During ripening, Cm-HMGR mRNA levels increased markedly in the fruit. In parallel with mRNA expression, Cm-HMGR activity increased af ter pollination, whereas no Cm-HMGR activity was detectable during fruit ri pening. Our results suggest that Cm-HMGR is important during early post-pol lination development of the fruit in melon.