A Feed-Forward Loop Consisting of the Response Regulator RpaB and the Small RNA PsrR1 Controls Light Acclimation of Photosystem I Gene Expression in the Cyanobacterium Synechocystis sp. PCC 6803

In this study, we found that the HLR1 DNA-binding motif, the recognition sequence for RpaB, is highly conserved in the core promoter region of the psrR1 gene among cyanobacterial species. Gel mobility shift assay revealed that RpaB binds to the HLR1 sequence of psrR1 in vitro. RNA gel blot analysis together with chromatin affinity purification (ChAP) analysis suggested that PSI genes are activated and the psrR1 gene is repressed by the binding of RpaB under low-light (LL) conditions. A decrease in DNA binding affinity of RpaB occurs within 5 min after the shift from LL to HL conditions, leading to the prompt decrease in PSI promoter activity together with derepression of psrR1 gene expression. Accumulating PsrR1 molecules then prevent translation from pre-existing PSI transcripts. By this dual repression at transcriptional and post-transcriptional levels, rapid and strict down-regulation of PSI expression under HL is secured. Our findings suggest that RpaB and PsrR1 constitute a feed-forward loop for the regulation of PSI gene expression to achieve a rapid acclimation response to the damaging HL conditions.
Source: Plant and Cell Physiology - Category: Cytology Authors: Tags: Regular Papers Source Type: research