Plasticity in the proteome of Emiliania huxleyi CCMP 1516 to extremes of light is highly targeted

Abstract

SummaryOptimality principles are often applied in theoretical studies of microalgal ecophysiology to predict changes in allocation of resources to different metabolic pathways, and optimal acclimation is likely to involve changes in the proteome, which typically accounts for > 50% of cellular nitrogen (N).We tested the hypothesis that acclimation of the microalga Emiliania huxleyi CCMP 1516 to suboptimal vs supraoptimal light involves large changes in the proteome as cells rebalance the capacities to absorb light, fix CO 2 , perform biosynthesis and resist photooxidative stress.Emiliania huxleyi was grown in nutrient-replete continuous culture at 30 (LL) and 1000 lmol photons m À2 s À1 (HL), and changes in the proteome were assessed by LC-MS/MS shotgun proteomics. Changes were most evident in proteins involved in the light reactions of photosynthesis; the relative abundance of photosystem I (PSI) and PSII proteins was 70% greater in LL, light-harvesting fucoxanthin-chlorophyll proteins (Lhcfs) were up to 500% greater in LL and photoprotective LI818 proteins were 300% greater in HL. The marked changes in the abundances of Lhcfs and LI818s, together with the limited plasticity in the bulk of the E. huxleyi proteome, probably reflect evolutionary pressures to provide energy to maintain metabolic capabilities in stochastic light environments encountered by this species in nature.

The trade‐off between the light‐harvesting and photoprotective functions of fucoxanthin‐chlorophyll proteins dominates light acclimation in Emiliania huxleyi (clone CCMP 1516)

“…The number of RCII per cell is typically quantified by measuring the abundances of PSII and PSII reaction centre proteins using either biophysical techniques (Falkowski et al ., ) or Western blotting (Six et al ., ), whereas photosynthetic unit size is typically quantified by the ratio Chl a :RCII. In E. huxleyi the proportion of the proteome attributable to PSII was greater in LL than HL (McKew et al ., ), and the ratio Lhcf:PSII was also significantly greater in LL compared to HL (Fig. ), consistent with previous observations that photoacclimation in this species involves changes of both photosynthetic unit size and number (Suggett et al ., ).…”

“…Our recent findings (McKew et al ., ) indicated that the photosynthetic proteins accounted for a greater proportion of the total proteome in LL, and in addition that the relative abundances of specific photosynthetic proteins also changed significantly between HL and LL. We reanalysed these data by first normalizing to the abundance of PSII core complex proteins (sum of spectral counts for detected proteins PsbA, B, C, D, E, H and V) as an internal photosynthetic unit reference before taking the ratio of these PSII‐normalized relative abundances between LL and HL (Fig.…”

Differential gene expression is tied to photochemical efficiency reduction in virally infected Emiliania huxleyi

“…E. huxleyi is well known for its tolerance to high light and has been shown to resist photoinhibition at light intensities up to 1500 µmol photons m −2 s −1 (Nanninga & Tyrrell 1996). Surprisingly, a recent proteomic study found that such adaptation to high light did not involve enhanced production of FtsH or HCF136 (McKew et al 2013b), even though net D1 repair rates increased in cultures exposed to high photon flux densities (McKew et al 2013a). While these data suggest that other factors may be important to determine the rate of D1 repair in E. huxleyi, they also underscore the importance of FtsH and HCF136 in maintaining PSII integrity and function under a variety of environmental conditions.…”

“…imicrobe.us/project/view/104). In addition, a recent E. huxleyi proteomic study only detected SOD2A (364889) out of the 4 annotated isoforms (McKew et al 2013b), suggesting that MnSOD…”

Bridging the gap between omics and earth system science to better understand how environmental change impacts marine microbes

“…Species-specific transcriptomics, proteomics and metabolomics studies with marine microbes provided first insights into the significance of single genes or gene clusters for acclimation and adaptation of marine microbes to environmental conditions (e.g. Mock et al, 2008;Allen et al, 2008;Wecker et al, 2009;Zinser et al, 2009, Ashworth et al, 2013, McKew et al, 2013. Furthermore, those studies laid the foundation for biomarker discoveries to study natural communities.…”