Identification of Components Associated with Thermal Acclimation of Photosystem II in Synechocystis sp. PCC6803

Abstract

BackgroundPhotosystem II (PSII) is the most thermally sensitive component of photosynthesis. Thermal acclimation of this complex activity is likely to be critically important to the ability of photosynthetic organisms to tolerate temperature changes in the environment.Methodology/FindingsWe have analysed gene expression using whole-genome microarrays and monitored alterations in physiology during acclimation of PSII to elevated growth temperature in Synechocystis sp. PCC 6803. PSII acclimation is complete within 480 minutes of exposure to elevated temperature and is associated with a highly dynamic transcriptional response. 176 genes were identified and classified into seven distinct response profile groups. Response profiles suggest the existence of an early transient phase and a sustained phase to the acclimation response. The early phase was characterised by induction of general stress response genes, including heat shock proteins, which are likely to influence PSII thermal stability. The sustained phase consisted of acclimation-specific alterations that are involved in other cellular processes. Sustained responses included genes involved in phycobillisome structure and modification, photosynthesis, respiration, lipid metabolism and motility. Approximately 60% of genes with sustained altered expression levels have no known function. The potential role of differentially expressed genes in thermotolerance and acclimation is discussed. We have characterised the acclimation physiology of selected gene ‘knockouts’ to elucidate possible gene function in the response.Conclusions/SignificanceAll mutants show lower PSII rates under normal growth conditions. Basal PSII thermotolerance was affected by mutations in clpB1, cpcC2, hspA, htpG and slr1674. Final PSII thermotolerance was affected by mutations in cpcC2, hik34, hspA and hypA1, suggesting that these gene products play roles in long-term thermal acclimation of PSII.

The wheat chloroplastic small heat shock protein (sHSP26) is involved in seed maturation and germination and imparts tolerance to heat stress

“…Photosystem II (PSII) has long been described as the most thermo‐sensitive process during photosynthesis (Berry & Bjorkman 1980; Aminaka et al . 2006; Rawland et al . 2010).…”

Physical Interaction between Bacterial Heat Shock Protein (Hsp) 90 and Hsp70 Chaperones Mediates Their Cooperative Action to Refold Denatured Proteins

“…As in other prokaryotes, the expression of HtpGs in cyanobacteria such as Synechococcus elongatus PCC 7942 and Synechocystis sp. PCC 6803 is highly induced upon transfer to high temperature, but in contrast to heterotrophic bacteria, mutation of the htpG gene impairs growth and/or survival of the two cyanobacterial strains greatly under heat stress, although HtpG is nonessential under normal conditions (11,12). Not only high temperature but also low temperature and oxidative stresses cause impaired phenotype of the Synechococcus htpG mutant (13,14).…”

Biological activity of microalgae can be enhanced by manipulating the cultivation temperature and irradiance

“…To survive, cells trigger different mechanisms such as an increase in enzyme synthesis [54], restoring the fluidity of membranes by increasing the proportion of unsaturated to saturated fatty acids, an increase of cis-double bonds and shortening of fatty acid chains [55,56]. Reduction of algal growth at high temperatures is related to denaturation and degradation of some proteins [57], disturbed functions of cell membranes due to changes in their composition and physical state [58], reduced functionality of the photosynthetic machinery especially of photosystem II (PSII) [59], decreased RUBISCO activity and/or its activase and stimulated respiration [60].…”