Does 2‐phosphoglycolate serve as an internal signal molecule of inorganic carbon deprivation in the cyanobacterium S ynechocystis sp. PCC 6803?

Abstract

Summary Cyanobacteria possess CO 2 ‐concentrating mechanisms ( CCM ) that functionally compensate for the poor affinity of their ribulose‐1,5‐bisphosphate carboxylase/oxygenase ( R ubisco) to CO 2 . It was proposed that 2‐phosphoglycolate (2 PG ), produced by the oxygenase activity of R ubisco and metabolized via photorespiratory routes, serves as a signal molecule for the induction of CCM ‐related genes under limiting CO 2 level ( LC ) conditions. However, in vivo evidence is still missing. Since 2 PG does not permeate the cells, we manipulated its internal concentration. Four putative phosphoglycolate phosphatases ( PGP ases) encoding genes ( slr0458 , sll1349 , slr0586 and slr1762 ) were identified in the cyanobacterium S ynechocystis PCC 6803. Expression of slr0458 in E scherichia coli led to a significant rise in PGP ase activity. A S ynechocystis mutant overexpressing ( OE ) slr0458 was constructed. Compared with the wild type (WT), the mutant grew slower under limiting CO 2 concentration and the intracellular 2 PG level was considerably smaller than in the wild type, the transcript abundance of LC ‐induced genes including cmpA , sbtA and ndhF3 was reduced, and the OE cells acclimated slower to LC – indicated by the delayed rise in the apparent photosynthetic affinity to inorganic carbon. Data obtained here implicated 2 PG in the acclimation of this cyanobacterium to LC but also indicated that other, yet to be identified components, are involved.

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