3-Hydroxy-3-methylglutaryl coenzyme A reductase 1 (HMG1) is highly associated with the cell division during the early stage of fruit development which determines the final fruit size in Litchi chinensis

3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR, EC: 1.1.1.34), an enzyme catalyzing the first committed step in the mevalonic acid (MVA) pathway for the biosynthesis of isoprenoids, has been reported to be involved in the fruit size determination through the regulation of early cell division. In litchi, the cell number achieved by this early cell division determines the final fruit size, but whether HMGR plays any role in this process was unknown. In this study, we set out to address this question with gene cloning and expression analysis in fruits of different pheno- or genotypes. We found that the litchi genome includes two HMGR homologues, denoted as LcHMG1 and LcHMG2. Despite 70% sequence identity at the amino acid level, they exhibited distinct expression patterns during litchi fruit development. LcHMG1 expression was highest in the early stage of fruit development, correlated with the high level of cell division. Absolute levels of LcHMG1 expression varied among fruits of different pheno- or genotypes, with expression in large-fruited types reaching higher levels for longer duration compared to that in small-fruited types. The expression patterns for LcHMG1 strongly suggest that this gene is involved in early cell division and fruit size determination in litchi. In contrast, LcHMG2 was most highly expressed in the late stage of fruit development, in association with biosynthesis of isoprenoid compounds required for later cell enlargement. These findings provided new insights on the function of HMGR genes during fruit development.

► Two HMGR genes were isolated from a fruit crop litchi.
► We examined the relationship between cell division activity and HMGR gene expression.
► LcHMG1 accumulated to a higher level in large-fruited pheno- or genotypes.
► LcHMG1 was highly correlated with the early cell division activity.
► LcHMG2 is related to the cell enlargement in late fruit development.