Photomixotrophic growth protein A (PmgA) regulates carbohydrate metabolism through the non-coding RNA Ncr0700/PmgR1 in the cyanobacterium Synechocystis sp. PCC 6803. Synechocystis sp. PCC 6803

Carbohydrate metabolism is a tightly regulated process in photosynthetic organisms. The ability to utilize glucose for growth and to regulate storage carbohydrate (i.e. glycogen) metabolisms requires a number of regulatory elements. In the cyanobacterium Synechocystis sp. PCC 6803, the photomixotrophic growth protein A (PmgA), a putative serine/threonine kinase, is involved in governing these abilities; however its downstream regulatory elements are not well studied. Here a genome-wide microarray analysis of a ∆pmgA strain revealed altered transcript levels of several non-coding RNAs, among them Ncr0700 was the most strongly reduced transcript. Generally, Ncr0700 is highly conserved among cyanobacteria. In Synechocystis its expression is light-dependent, i.e. the abundance is reciprocal to the light intensity. Compared to WT and similar to a ΔpmgA mutant, a ∆ncr0700 deletion strain showed a ~2 fold increase in glycogen content under photoautotrophic conditions. Under these conditions ∆ncr0700 grew similarly to the wild type; in contrast its growth was arrested after a shift to photomixotrophic conditions. Ectopic expression of Ncr0700 in ∆ncr0700 as well as ∆pmgA restored both the glycogen and photomixotrophic growth to the wild type levels. These results indicate that Ncr0700 plays a role in regulation of carbohydrate metabolism, acts downstream of PmgA and therefore is renamed here to PmgR1 for photomixotrophic growth RNA 1. Overall design: We analyzed gene expression in Synechocystis sp. PCC 6803 WT as well as a ∆pmgA (sll1968) mutant grown at 50 μmol photons m–2 s–1 at 30°C with continuous bubbling with air supplemented with 3% (v/v) CO2. Three biological replicates were analyzed for ΔpmgA and compared with 2 replicate cultures of WT.