Figure 1.
Hypothesized chlorophyll a and steroid biosynthetic pathways in P. tricornutum.
Colored squares indicate the regulation pattern of genes encoding putative enzymes functioning in the two pathways after exposure to HL for 0.5 h, 3 h, 6 h, 12 h, 24 h and 48 h. Squares with a diagonal line inside indicate genes with an expression ratio greater than +/−0.5 that are not significantly regulated. The asterisk marking the expression pattern of subunit I of Mg-chelatase (MgCh) indicates that the gene is chloroplast encoded. The scale on the right represents gene expression ratio values, log2 transformed. The gene encoding Mg-protoporphyrin IX monomethyl ester cyclase responsible for converting Mg-protoporphyrin IX monomethyl ester to divinyl protochlorophyllide a in higher plants [30] is absent in P. tricornutum, and this step is marked with a question mark in the figure. The abbreviations used are: GLURS: glutamyl-tRNA synthetase; HEMA: glutamyl-tRNA reductase; HEML: glutamate-1-semialdehyde 2,1-aminomutase, HEMB: porphobilinogen synthase; HEMC: hydroxymethylbilane synthase; HEMD: uroporphyrinogen-III synthase; HEME: uroporphyrinogen decarboxylase; HEMF: coproporphyrinogen III oxidase; PPO: protoporphyrinogen oxidase; MgCh: magnesium chelatase; CHLM: Mg-protoporphyrin IX methyl transferase; POR: protochlorophyllide oxidoreductase; DVR: divinyl protochlorophyllide a 8-vinyl reductase; CHLG: chlorophyll synthase; DXS: deoxyxylulose-5-phosphate synthase; DXR: 1-deoxy-D-xylulose 5-phosphate reductoisomerase; ISPD: 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase; CMK: 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase; ISPF: 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase; HDS: 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate synthase; HDR: 4-hydroxy-3-methylbut-2-enyl diphosphate reductase; FDPS: farnesyl diphosphate synthase; GGPS: geranylgeranyl pyrophosphate synthase; IDI: isopentenyl pyrophosphate:dimethylallyl pyrophosphate isomerise; CHLP: geranylgeranyl reductase.
Figure 2.
Hypothesized carotenoid biosynthetic pathway in P. tricornutum according to Coesel et al. [32].
Colored squares indicate the regulation pattern of genes encoding putative enzymes involved in the synthesis of carotenoids after exposure to HL for 0.5 h, 3 h, 6 h, 12 h, 24 h and 48 h. Squares with a diagonal line inside indicate genes with an expression ratio (log2 transformed) greater than +/−0.5 that are not significantly regulated. The scale on the right represents gene expression ratio values, log2 transformed. The violaxanthin cycle (A) and the diadinoxanthin cycle (B) are boxed. Dashed arrows indicate the hypothetical conversion of violaxanthin to diadinoxanthin and the formation of fucoxanthin from diadinoxanthin, as proposed by Lohr and Wilhelm [52], [53]. The abbreviations used are PSY: phytoene synthase; PDS: phytoene desaturase; ZDS: ζ-carotene desaturase, CRTISO: carotenoid isomerase; crtI: bacterial-like desaturase; LCYB: lycopene β-cyclase; LUT: lutein deficient-like; ZEP: zeaxanthin epoxidase; VDE: violaxanthin de de-epoxidase; VDL: violaxanthin de de-epoxidase-like; VDR: violaxanthin de de-epoxidase related.
Figure 3.
Regulation pattern of HL affected genes during the acclimation period.
The differentially regulated genes encode proteins involved in light sensing, antenna proteins, photoreceptors, components involved in oxidative photosynthesis, carbon metabolism, Calvin cycle and ROS scavenging systems after exposure to HL for 0.5 h, 3 h, 6 h, 12 h, 24 h and 48 h. The color code indicates expression values. Squares with a diagonal line inside indicate genes with an expression ratio (log2 transformed) greater than +/−0.5 that are not significantly regulated. Genes where at least one of the probes representing the genes were significantly regulated by >2-fold at least at one time point during the acclimation period, were included in the figure. The expression patterns of genes marked with an asterisk are chloroplast encoded. The scale on the right represents gene expression ratio values, log2 transformed. The abbreviations used are LHCF: major fucoxanthin Chl a/c proteins; LHCR: red algal-like proteins; LHCX: LI818-like proteins; LHC#: unclassified light harvesting proteins; Psa: PSI proteins; PETJ: cytochrome c6; Psb: PSII proteins; HCF: high Chl fluorescence; FtsH: Filamentation temperature sensitive H; AUR: aureochrome; CRYL: cryptochrome-like protein; CPF: cryptochrome; SKP3: Sensor Kinase Protein 3; PPDK: pyruvate-phosphate dikinase; PEPCase: phosphoenolpyruvate carboxylase; MDH: malate dehydrogenase; PEPCK: phosphoenolpyruvate carboxykinase; PK: pyruvate kinase; PYC: pyruvate carboxylase; CA: carbonic anhydrase; SLC4A: bicarbonate transporter; OMT: oxoglutarate/malate transporter; FBPC: fructose-1,6-bisphosphatase; FBAC: fructose-1,6-bisphosphate aldolase; GPI: glucose-6-phosphate isomerase; TPI: triosephosphate isomerase; GLRXC: glutaredoxin; TRX: thioredoxin; TRXLl: thioredoxin-like; PRX: peroxiredoxin; GPX: glutathione peroxidase; APX: ascorbate peroxidise; SOD: superoxide dismutase; GST: glutathione S-transferase; TMT: gamma-tocopherol methyltransferase; TYPA: tyrosine phosphorylation protein A.
Figure 4.
Main [LHPs] per cell and their ratio as a function of HL exposure time.
The Chl a, Chl c and Fuco concentrations per cell and the ratio of Fuco plus Chl c to Chl a as a function of high-light (500 µmol m−2s−1) exposure time. Incubation was performed in a LL (35 µmol m−2s−1) exponentially growing 10L batch culture 3 weeks prior to HL exposure. The 0 h sample value is the mean of the 18 LL control samples (blue symbol). HL exposure values are the mean of three biological parallels. Values are presented with±SD bars.
Figure 5.
De-epoxidation state index (DES) and change in [Fuco], [DD] and [DT] per cell.
A) De-epoxidation state index (DES) index calculated from the HPLC pigment data. The 0 h sample value is the mean of the 18 LL control samples (blue symbol). HL exposure values are the mean of three biological parallels. Incubations as in Figure 4. Values are presented with±SD bars. (B) Change in Fucoxanthin, Diadinoxanthin and Diatoxanthin cell concentration as a function of high light exposure time. Change in pigment concentration for Fuco (normalized to LL, t = 0 h), DD (as for Fuco) and DT (normalized to HL at 0.5 h) as a function of time after HL exposure. Values are average of three parallel HPLC samples. Incubations as in Figure 4.
Figure 6.
The maximum quantum yield after HL exposure.
The maximum quantum yield (Fv/Fm) as a function of time after exposure to HL (500 µmol m−2 s−1, red squares, solid line) and LL (35 µmolm−2 s−1, blue circles, dashed line) measured using variable fluorescence (PAM) after keeping the samples for 3 min in the dark. Bars are S.D. (n = 3).
Figure 7.
The photosynthetic capacity and the light-saturation index.
The A) maximum photosynthetic capacity ( i.e. maximum light-saturated rETR) and B) the light-saturation index versus time after exposure to HL (500 µmol m−2 s−1, red squares, solid line) and LL (35 µmol m−2 s−1, blue circles, dashed line), calculated from the photosynthesis vs. irradiance relationship measured using variable Chl a fluorescence (PAM). Bars are S.D. (n = 3).
Table 1.
Summary of the most important processes in protection and acclimation to high light (HL) in P. tricornutum.