Abstract
Terpenes are the largest and most diverse class of secondary metabolites in plants and play a very important role in plant adaptation to environment. 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is a rate-limiting enzyme in the process of terpene biosynthesis in the cytosol. Previous study found the HMGR genes underwent gene expansion in Gossypium raimondii, but the characteristics and evolution of the HMGR gene family in Gossypium genus are unclear. In this study, genome-wide identification and comparative study of HMGR gene family were carried out in three Gossypium species with genome sequences, i.e., G. raimondii, Gossypium arboreum, and Gossypium hirsutum. In total, nine, nine and 18 HMGR genes were identified in G. raimondii, G. arboreum, and G. hirsutum, respectively. The results indicated that the HMGR genes underwent gene expansion and a unique gene cluster containing four HMGR genes was found in all the three Gossypium species. The phylogenetic analysis suggested that the expansion of HMGR genes had occurred in their common ancestor. There was a pseudogene that had a 10-bp deletion resulting in a frameshift mutation and could not be translated into functional proteins in G. arboreum and the A-subgenome of G. hirsutum. The expression profiles of the two pseudogenes showed that they had tissue-specific expression. Additionally, the expression pattern of the pseudogene in the A-subgenome of G. hirsutum was similar to its paralogous gene in the D-subgenome of G. hirsutum. Our results provide useful information for understanding cytosolic terpene biosynthesis in Gossypium species.
Highlights
Terpenes are a type of natural compound, which are widely distributed in nature and have diverse structures and functions [1,2]
The candidate hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) genes were identified from the Gossypium genome using the local blast program with the query sequences of Arabidopsis HMGR genes
Nine, nine and 18 putative HMGR genes were identified in G. raimondii, G. arboreum, and G. hirsutum, respectively (Table 1 and Supplementary Materials Table S3)
Summary
Terpenes are a type of natural compound, which are widely distributed in nature and have diverse structures and functions [1,2]. Terpenes are synthesized by two independent pathways: the mevalonate pathway (MVA pathway) in the cytosol and the 2-C-methyl-D-erythritol 4-phosphate pathway (MEP pathway) in the plastid [7,8]. The 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) catalyzes the conversion of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) to mevalonate (MVA), which is considered to be a rate-limiting enzyme of the MVA pathway and plays a key role in the biosynthesis of plant cytosolic terpenes [9,10]. Many experiments have shown that HMGR holds an important control point in the MVA pathway and genetic manipulation of HMGR increased terpenes content in plants.
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