An Integrated Analysis of Molecular Acclimation to High Light in the Marine Diatom Phaeodactylum tricornutum

Abstract

Photosynthetic diatoms are exposed to rapid and unpredictable changes in irradiance and spectral quality, and must be able to acclimate their light harvesting systems to varying light conditions. Molecular mechanisms behind light acclimation in diatoms are largely unknown. We set out to investigate the mechanisms of high light acclimation in Phaeodactylum tricornutum using an integrated approach involving global transcriptional profiling, metabolite profiling and variable fluorescence technique. Algae cultures were acclimated to low light (LL), after which the cultures were transferred to high light (HL). Molecular, metabolic and physiological responses were studied at time points 0.5 h, 3 h, 6 h, 12 h, 24 h and 48 h after transfer to HL conditions. The integrated results indicate that the acclimation mechanisms in diatoms can be divided into an initial response phase (0–0.5 h), an intermediate acclimation phase (3–12 h) and a late acclimation phase (12–48 h). The initial phase is recognized by strong and rapid regulation of genes encoding proteins involved in photosynthesis, pigment metabolism and reactive oxygen species (ROS) scavenging systems. A significant increase in light protecting metabolites occur together with the induction of transcriptional processes involved in protection of cellular structures at this early phase. During the following phases, the metabolite profiling display a pronounced decrease in light harvesting pigments, whereas the variable fluorescence measurements show that the photosynthetic capacity increases strongly during the late acclimation phase. We show that P. tricornutum is capable of swift and efficient execution of photoprotective mechanisms, followed by changes in the composition of the photosynthetic machinery that enable the diatoms to utilize the excess energy available in HL. Central molecular players in light protection and acclimation to high irradiance have been identified.

An atypical member of the light-harvesting complex stress-related protein family modulates diatom responses to light

“…Their accumulation upon light stress has been associated with enhanced photoprotection in the green freshwater alga Chlamydomonas reinhardtii (15). A similar role was recently proposed for diatom orthologs that are upregulated in high light (16)(17)(18). On the other hand, gene expression analyses revealed that one of the four LHCX genes of P. tricornutum (LHCX1) is not light-stress responsive ( Fig.…”

Diatom Phytochromes Reveal the Existence of Far-Red-Light-Based Sensing in the Ocean

“…The comparison of Pt-DPH absorption spectra with the action spectra for gene expression showed that maximal induction of selected FR-responsive genes occurs at wavebands specific to the Pfr form. Analyses of these genes in transcriptome data sets from P. tricornutum cells exposed to other wavebands (blue, green, red, and white) (Nymark et al, 2009;Chauton et al, 2013;Valle et al, 2014) showed either no expression changes or opposite changes compared with those induced by FR. The loss of responsiveness of Class 1 genes in knockout cells further demonstrated the involvement of DPH in FR light signaling (Figure 3).…”

Zeaxanthin Binds to Light-Harvesting Complex Stress-Related Protein to Enhance Nonphotochemical Quenching in Physcomitrella patens

“…In P. patens, the upregulation by zeaxanthin of the LHCSR-dependent NPQ component is far stronger than the complementary PSBS-dependent component, leading to a strong control of zeaxanthin over NPQ to a level unprecedented in green algae and plants (Figures 2B and 2C). High zeaxanthin dependence of NPQ amplitude was reported in diatoms (Coesel et al, 2008;Nymark et al, 2009;Bailleul et al, 2010). While NPQ is decreased in a LHCSR knockdown genotype (lhcx1), clear evidence that LHCSR is the only agent for NPQ is lacking in these algae (Lavaud et al, 2012).…”