The cAMP receptor protein, SyCRP1 acts as a transcriptional repressor of CO2-concentrating mechanism genes at high inorganic carbon levels in Synechocystis PCC 6803

Abstract

Cyanobacteria utilize a CO₂-concentrating mechanism (CCM) to enhance photosynthetic efficiency by accumulating CO₂ around RuBisCO, a process crucial for adapting to fluctuating environmental CO₂ levels. While the upregulation of CCM genes under low inorganic carbon (C_i) conditions is known, the precise C_i sensing and regulatory mechanisms governing CCM gene expression remain incompletely understood. We show that a membrane-bound SyCRP1 senses high C_i levels through cAMP binding to its low- and high-affinity sites. We demonstrate its interaction with membrane lipids and liposomes, and a subsequent reversal of its membrane localization upon cAMP binding. Comprehensive ChIP-seq analysis reveals direct binding of SyCRP1 to regulatory elements of core CCM genes. Our findings establish SyCRP1 as a key transcriptional repressor of these genes under high C_i conditions, significantly advancing our understanding of the molecular mechanisms governing CCM genes' expression in cyanobacteria.