Identification of photosynthetic NAD-capped RNAs in Cyanobacteria: Towards Functional Insights

Nicotinamide adenine dinucleotide (NAD+)-capped RNAs (NAD-RNAs) have been discovered in prokaryotic, eukaryotic and archaeal organisms including Arabidopsis and rice plants. However, NAD-RNAs in cyanobacteria, prokaryotes with photosynthetic systems akin to higher plants, have not been reported till now. Using a highly sensitive and accurate method recently reported for profiling NAD-capped transcriptomes, we generated NAD-RNA profiles in cyanobacteria and found that photosynthetic NAD-RNAs were mainly produced from genes coding for PS II. In addition, we generated NAD-capped transcriptomes in cyanobacteria grown in the dark. Differential expression of NAD-RNAs between dark and light conditions, coupled with expression patterns of regular RNAs revealed by RNA-seq, reveals distinct regulatory mechanisms of NAD-RNA. Based on these findings, we conducted a focal study on psbQ, one of the top NAD-RNA-producing genes for functional study. Through marker-less point mutation of TSS (A) to G to block NAD-psbQ RNA synthesis, we observed growth inhibition in the mutant, while regular psbQ RNA level remained unaltered, indicating a potential role for psbQ NAD-RNA in regulating the translation of its native RNA counterpart.