RpaA Regulates the Accumulation of Monomeric Photosystem I and PsbA under High Light Conditions in Synechocystis sp. PCC 6803

Abstract

The response regulator RpaA was examined by targeted mutagenesis under high light conditions in Synechocystis sp. PCC 6803. A significant reduction in chlorophyll fluorescence from photosystem I at 77 K was observed in the RpaA mutant cells under high light conditions. Interestingly, the chlorophyll fluorescence emission from the photosystem I trimers at 77 K are similar to that of the wild type, while the chlorophyll fluorescence from the photosystem I monomers was at a much lower level in the mutant than in the wild type under high light conditions. The RpaA inactivation resulted in a dramatic reduction in the monomeric photosystem I and the D1 protein but not the CP47 content. However, there is no significant difference in the transcript levels of psaA or psbA or other genes examined, most of which are involved in photosynthesis, pigment biosynthesis, or stress responses. Under high light conditions, the growth of the mutant was affected, and both the chlorophyll content and the whole-chain oxygen evolution capability of the mutant were found to be significantly lower than those of the wild type, respectively. We propose that RpaA regulates the accumulation of the monomeric photosystem I and the D1 protein under high light conditions. This is the first report demonstrating that inactivation of a stress response regulator has specifically reduced the monomeric photosystem I. It suggests that PS I monomers and PS I trimers can be regulated independently for acclimation of cells to high light stress.

The role of the Synechocystis sp. PCC 6803 homolog of the circadian clock output regulator RpaA in day–night transitions

“…As reported from Majeed et al . (), ∆ rpaA displays a reduced phycocyanin (628 nm) to chlorophyll (680 nm) ratio compared to the WT, which is comparable to the phenotype of the ∆ rpaA strain, constructed in our study. The entire absorbance spectrum of ∆ rpaA /FLAG‐ rpaA resembles the WT spectrum, confirming the complementation of the ∆ rpaA phenotype by FLAG‐RpaA (Fig.…”

“…Majeed et al . () reported a specific effect of rpaA deletion on photosynthetic complexes in high light. However, these studies did not analyze the behavior of the mutant in a light‐dark cycle.…”

“…In another study, Majeed et al . () analyzed a Synechocystis 6803 rpaA inactivation mutant, with a focus on regulation of photosystem assembly under high‐light stress. They propose that the accumulation of monomeric photosystem I complexes and the D1 protein of photosystem II are under control of RpaA.…”

The Small Regulatory RNA SyR1/PsrR1 Controls Photosynthetic Functions in Cyanobacteria

“…Highlight acclimation is achieved by the interplay of transcriptional regulation by transcription factors (gray lines), s-factors (not included in the model), and posttranscriptional regulation by PsrR1 (blue lines). mechanism (Majeed et al, 2012). The transcriptional regulator PedR activates the expression of chlN, chlB, and chlL mRNAs (Nakamura and Hihara, 2006), which encode subunits of the lightindependent protochlorophyllide reductase under low-light conditions.…”

A Transcriptional Regulator Sll0794 Regulates Tolerance to Biofuel Ethanol in Photosynthetic Synechocystis sp. PCC 6803

“…Two proteins related to bacterial two-component signal transduction, Sll1871 of a HepK two-component system sensory histidine kinase and Slr0115 of a response regulator, were down-regulated in the ⌬sll0794 mutant. In the previous study, it has been found that Slr0115 regulates the accumulation of the monomeric photosystem I and the D1 protein under high light stress conditions (54).…”