Expanding, clustering and high expression of HMGR in S. rosmarinus
leaf tissue
To investigate the genetic basis of monoterpene accumulation, we
analyzed the first key enzyme in the monoterpene synthesis pathway,
3-hydroxy-3-methylglutaryl-CoA reductase (HMGR ). Our gene family
contraction and expansion analysis showed that the family of genes
encoding SrHMGR was expanded in S. rosmarinus compared to
sister clades, with 12 copies in S. rosmarinus and only 6 inS. miltiorrhiza (Table S22). To further understand the expansion
of genes encoding SrHMGR , we constructed a maximum likelihood
(ML) tree of HMGRs from 24 species and found that HMGRscould be divided into three subgroups (Figure S18). SrHMGR7 ,SrHMGR9 , SrHMGR10 and SrHMGR12 were grouped in the
same sub-clade with high amino acid sequence identity (88.87%–97.96%)
(Table S24). These genes clustered within 0.19 Mb on pseudochromosome 7
(Table S25),. indicating SrHMGR genes on pseudochromosome 7 had
expanded and replicated in clusters in S. rosmarinus. Covariance
analysis of HMGRs in S. rosmarinus , S.
miltiorrhiza , S. baicalensis , and S. splendens confirmed
that the expanded SrHMGR genes on pseudochromosome 7 may be an
important genetic basis for monoterpene accumulation (Figure S17).
Additionally, transcriptome data showed that SrHMGR7 ,SrHMGR9 , SrHMGR10 , and SrHMGR12 were expressed at
2.40-fold higher levels overall in leaves than in roots of S.
rosmarinus (Figure 4), suggesting that the upregulation of HMGRexpression in the MVA pathway may facilitate the biosynthesis of
monoterpenes.