UV-B-induced Differential Transcription of psbAGenes Encoding the D1 Protein of Photosystem II in the Cyanobacterium Synechocystis 6803

Abstract

UV-B irradiation of intact Synechocystis sp. PCC 6803 cells results in the loss of photosystem II activity, which can be repaired via de novo synthesis of the D1 (and D2) reaction center subunits. In this study, we investigated the effect of UV-B irradiation on the transcription of the psbA2 and psbA3 genes encoding identical D1 proteins. We show that UV-B irradiation increases the level of psbA2 mRNA 2-3-fold and, more dramatically, it induces a 20 -30-fold increase in the accumulation of the psbA3 mRNA even at levels of irradiation too low to produce losses of either photosystem II activity or D1 protein.The induction of psbA3 transcript accumulation is specific for UV-B light (290 -330 nm). Low intensity UV-A emission (330 -390 nm) and white light induce only a small, at most, 2-3-fold enhancement, whereas no effect of blue light was observed. Expression patterns of chimeric genes containing the promoter regions of the psbA2, psbA3 genes fused to the firefly luciferase (luc) reporter gene indicate that (i) transcription of psbA2/luc and psbA3/luc transgenes was elevated, similarly to that of the endogenous psbA genes, by UV-B irradiation, and that (ii) a short, 80-base pair psbA3 promoter fragment is sufficient to maintain UV-B-induced transcription of the luc reporter gene. Furthermore, our findings indicate that UV-B-induced expression of the psbA2 and psbA3 genes is a defense response against UV-B stress, which is regulated, at least, partially at the level of transcription and does not require active electron transport.Recent reductions in the stratospheric ozone layer allowing more ultraviolet-B (UV-B, 280 -320 nm) radiation to reach the Earth's surface and ecologically significant depths of the ocean (1) have initiated extensive research efforts to elucidate molecular mechanisms regulating responses of various organisms to UV irradiation (2). In photosynthetic organisms, a crucial part of the overall UV-B effect is related to damage in the photosynthetic apparatus leading to decreased oxygen evolution and CO 2 fixation (3-6), reduction in dry weight, secondary sugars, starch, and total chlorophyll (7,8). Within the photosynthetic apparatus, the most sensitive UV-B target is the light energy converting complex of photosystem II (PSII) 1 (for reviews, seeRefs. 9 and 10), although photosystem I (4, 11), ribulosebisphosphate carboxylase/oxygenase (12, 13), and ATPase (14) can also be damaged. PSII is a large pigment-protein assembly embedded in the thylakoid membrane. Inhibition of PSII activity by UV-B radiation is accompanied by the degradation of the D1 and D2 protein subunits (15-18), which form the heart of the PSII reaction center by contributing ligands to cofactors that mediate primary photochemistry (for review, see Ref. 19). Photoheterotrophic cyanobacterium species are very useful model organisms for studying the adverse effects of UV-B irradiation on the activity of PSII because (i) cyanobacteria were among the earliest oxygenic photosynthetic organisms that were exposed early in their evolution...

A single plasmid based CRISPR interference in Synechocystis 6803 – A proof of concept

“…This gene has three paralogs in the Synechocystis genome, one of which ( psbA1 ) has a somewhat divergent DNA sequence and is hardly expressed under normal conditions [33]. The two other copies ( psbA2 and psbA3 ) [34] code for identical protein sequences and their DNA sequence similarity is so high that it was possible to design a common spacer targeting both of them (see S1 Fig).…”

Overexpression, Isolation, and Spectroscopic Characterization of the Bidirectional [NiFe] Hydrogenase from Synechocystis sp. PCC 6803

“…3B encodes for the D1 protein of photosystem II, which is damaged at a higher pace at high light intensities because of stronger photooxidation. Consequently, the cells increase the expression of this gene (50).…”

Photoinhibition of Photosystem II and photodamage of the oxygen evolving manganese cluster

“…The action spectrum of the repair of UV-photoinhibited PSII indicates dependence on photosynthesis [128], reflecting the dependence of the synthesis of D1 protein on functional photosynthesis [136,137]. In cyanobacteria, both UV and visible-light-induced photoinhibition cause an increase in the transcription of the psbA genes encoding the D1 protein [50,138,139]. Furthermore, acclimation to UV light causes similar metabolic changes in photosynthetic organisms as acclimation to high-intensity light, like faster repair of photoinhibited PSII [117] and switching to a high-light specific form of the D1 protein in cyanobacteria that have two forms of the D1 protein [132,133].…”