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