Fig. 3.
Carotenoid and plastoquinone/plastoquinol in chlamydomonad sp. NrCl902. a Predicted biosynthetic pathway of isoprenoids, carotenoids, and plastoquinol. Sequences in which plastid-targeting transit peptides were detected are shown by green circles with solid lines, whereas those lacking explicit plastid-targeting transit peptides are shown by green circles with no line. DXS: 1-deoxy-d-xylulose 5-phosphate synthase, DXR: 1-deoxy-d-xylulose 5-phosphate reductase, MCT: 2-C-methyl-d-erythritol 4-phosphate cytidylyltransferase, CMK: 4-diphosphocytidyl-2-C-methyl-d-erythritol kinase, MDS: 2-C-methyl-d-erythritol 2,4-cyclodiphosphate synthase, HDS: (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP) synthase, HDR: (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP) reductase, IPI: isopentenyl-diphosphate delta-isomerase, GDS: geranyl diphosphate synthase, SDS: solanesyl diphosphate synthase, TyrAT: tyrosine aminotransferase, HPD: 4-hydroxyphenylpyruvate dioxygenase, HST: homogentisate solanesyltransferase, MMT: MPBQ/MSBQ methyltransferase, GGDS: geranylgeranyl diphosphate synthase, PSY:, Z-ISO: 15-cis-ζ-carotene isomerase, PDS: phytoene desaturase, CrtISO: prolycopene isomerase, ZDS: ζ-carotene desaturase, CrtL-b: lycopene β cyclase, and CrtR: β-carotene hydroxylase (see also Table S1). b LC-MS/MS chromatograms (multiple reaction monitoring mode) of the directly analyzed acetone extract from chlamydomonad sp. NrCl902 (top) and the extract after oxidative treatment with ferric chloride (bottom), identifying plastoquinol-9 (PQH2-9), ubiquinol-9 (UQH2-9), plastoquinone-9 (PQ-9), and ubiquinone-9 (UQ-9). While a prominent peak at ca. 2.25 min nearly disappeared, another prominent peak appeared at ca. 4.50 min after oxidative treatment, suggesting that the latter compound was the oxidized product of the former; these were assigned as PQH2-9 and PQ-9, respectively, by comparing with the extract of cyanobacteria based on their retention times. Note that a trace amount of PQ-9 was present even before the oxidative treatment. c, d LC-MS/MS spectra (product ion scan mode) of compounds at ca. 2.25 and 4.50 min, confirming each as PQH2-9 and PQ-9, respectively