Schematic representation of isoprenoid and carotenoid pathways in plants. Enzymes whose encoding gene transcripts were analyzed by RT-qPCR are outlined in boldface. Steps involving multiple enzymes are outlined with dashed arrows. Gene/enzyme acronyms (in alphabetical order): CCD1 and CCD4, carotenoid cleavage dioxygenases 1 and 4; CHY-B, carotene β-hydroxylase; CHY-E, carotene ε-hydroxylase; CMK, 4-(cytidine 5'-diphospho)-2-C-methyl-d-erythritol kinase; CRTISO, carotenoid isomerase; DXR, 1-deoxy-d-xylulose 5-phosphate reductoisomerase; DXS, 1-deoxy-d-xylulose 5-phosphate synthase; HDR, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase; HDS, 4-hydroxy-3-methylbut-2-enyl diphosphate synthase; LCY-B, lycopene β-cyclase; LCY-E, lycopene-e-cyclase; MCT, 2-C-methyl-d-erythritol 4-phosphate cytidylyltransferase; MDS, 2-C-methyl-d-erythritol 2,4-cyclodiphosphate synthase; NCED1 and NCED2, 9-cis-epoxycarotenoid dioxygenases 1 and 2; PDS, phytoene desaturase; PSY, phytoene synthase; VDE, violaxanthin de-epoxidase; ZDS, ζ-carotene desaturase; ZEP, zeaxanthin epoxidase; Z-ISO, ζ-carotene isomerase. For a review on the processes and relationships involved in plant VOC biosynthesis pathways, the reader is referred to .