Volume 8, Issue 1, Pages 188-191 (January 2015) Multiple Levels of Regulation Determine Monoterpenoid Essential Oil Compositional Variation in the Mint Family  Amirhossein Ahkami, Sean R. Johnson, Narayanan Srividya, Bernd Markus Lange  Molecular Plant  Volume 8, Issue 1, Pages 188-191 (January 2015) DOI: 10.1016/j.molp.2014.11.009 Copyright © 2015 The Author Terms and Conditions

Figure 1 Evidence for Multilevel Regulation of Monoterpenoid Essential Oil Biosynthesis in Mint. (A) Genetic relationships among mint cultivars. (B) Outline of p-menthane monoterpene biosynthesis. The enzymes involved in this pathway are (−)-limonene synthase (LS); (−)-limonene 3-hydroxylase (L3H); (−)-trans-isopiperitenol dehydrogenase (ISPD); (−)-trans-isopiperitenone reductase (ISPR); (+)-cis-isopulegone isomerase (ISPI); (+)-menthofuran synthase (MFS); (+)-pulegone reductase (PR) ((−)-menthone-forming and (+)-isomenthone-forming activities); (−)-menthone:(−)-menthol reductase (MMR) (MMR1, (−)-menthol-forming activity; MMR2, (+)-neoisomenthol-forming activity); (−)-menthone:(+)-neomenthol reductase (MNR) (MNR1, (+)-neomenthol-forming activity; MNR2, (+)-isomenthol-forming activity); (−)-limonene 6-hydroxylase (L6H); and (−)-trans-carveol dehydrogenase (CDH). The biosynthetic reactions leading to the formation of signature monoterpenes are color coded (tan, spearmint; blue, watermint; and green, peppermint). (C) Expression patterns (based on RNAseq transcriptome data) of genes involved in p-menthane monoterpene biosynthesis in glandular trichomes of immature and mature leaves (leaves of 0.5–1.5 cm in length [top two pairs from the shoot tip] were harvested as “immature leaves”; the fifth leaf pair from the shoot tip constituted “mature leaves”; spearmint, black bars; watermint, gray bars; and peppermint, white bars). ISPD, (−)-trans-isopiperitenol dehydrogenase; ISPR, (−)-trans-isopiperitenone reductase; L3H, (−)-limonene 3-hydroxylase; L6H, (−)-limonene 6-hydroxylase; LS, (−)-limonene synthase; MFS, (+)-menthofuran synthase; MMR, (−)-menthone:(−)-menthol reductase; PR, (+)-pulegone reductase. (D) Real-time quantitative PCR analysis of transcript abundance in isolated glandular trichomes of immature leaves (for L3H, the expression levels of the most abundant isoform were quantified [PM2 in watermint and peppermint; PM17 in spearmint]). (E) Enzyme activities in microsomes isolated from glandular trichomes of immature leaves. (F) Genomic organization of the ISPR gene with promoter and an upstream inverted repeat. (G) DNA methylation analysis (as cytosine methylation percentage) of the ISPR promoter region in leaves (left), the ISPR gene in leaves (middle), and the ISPR gene in glandular trichomes (right). The asterisk indicates a significantly higher DNA methylation in glandular trichomes of spearmint compared to those of watermint/peppermint (P < 0.01). (H) Loss of ISPR gene expression in glandular trichomes of spearmint correlates with high DNA methylation levels. The bars with caps indicate SD in panels D, E, G, and H. Molecular Plant 2015 8, 188-191DOI: (10.1016/j.molp.2014.11.009) Copyright © 2015 The Author Terms and Conditions