Abstract: The 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is a key enzyme in the MVA biosynthesis pathway of terpenoids. To understand the phylogenetic of its coding gene HMGR and its molecular evolution and expression characteristics in the clade of loblolly pine, in this study, 19 representative species of HMGR sequences were selected for phylogenetic and molecular evolution analysis, and 5 different tissue parts of loblolly pine were used as materials to analyze the expression characteristics of HMGR. The results showed that the HMGR was relatively conserved in the evolution process. The average genetic distance between sequences was 0.323, and the average selection pressure was 0.1212, which indicated that HMGR was mainly subjected to the purifying selection during the evolution process. The selective pressure was 0.4293 in the clade of loblolly pine. Fourteen sites were detected to be positive selective, and the value of posterior probability was greater than 0.95, which indicated that the different selective pressure on each site of HMGR was significant. HMGR had the highest expression level in young leaves of loblolly pine, showing the tissue specific expression of HMGR.

Key words: loblolly pine, HMGR, molecular evolution, expression level