ppGpp Controls Global Gene Expression in Light and in Darkness in S. elongatus

• Published in: Cell reports (Cambridge) 2017-12, Vol.21 (11), p.3155-3165
• Main Authors: Puszynska, Anna M., O’Shea, Erin K.
• Format: Article
• Language: English
• Subjects: (p)ppGpp; cyanobacteria; gene expression; light/dark cycle; PCC7942; stringent response; Synechococcus elongatus
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2017.11.067

The bacterial and plant stringent response involves production of the signaling molecules guanosine tetraphosphate and guanosine pentaphosphate ((p)ppGpp), leading to global reorganization of gene expression. The function of the stringent response has been well characterized in stress conditions, but its regulatory role during unstressed growth is less studied. Here, we demonstrate that (p)ppGpp-deficient strains of S. elongatus have globally deregulated biosynthetic capacity, with increased transcription rate, translation rate, and cell size in unstressed conditions in light and impaired viability in darkness. Synthetic restoration of basal guanosine tetraphosphate (ppGpp) levels is sufficient to recover transcriptional balance and appropriate cell size in light and to rescue viability in light/dark conditions, but it is insufficient to enable efficient dark-induced transcriptional shutdown. Our work underscores the importance of basal ppGpp signaling for regulation of cyanobacterial physiology in the absence of stress and for viability in energy-limiting conditions, highlighting that basal (p)ppGpp level is essential in cyanobacteria in the environmental light/dark cycle. [Display omitted] •(p)ppGpp regulates the physiology of S. elongatus in light and in darkness•Basal levels of (p)ppGpp regulate transcription, translation, and cell size in light•Basal levels of ppGpp are sufficient to protect cell viability in the dark•(p)ppGpp accumulation is required for dark-induced transcriptional shutdown Puszynska and O’Shea characterize the role of the signaling molecule ppGpp in regulation of the physiology of Synechococcus elongatus. They find that basal levels of ppGpp control transcription, translation, and cell size in light and protect cell viability in darkness, and they show that ppGpp accumulation is required for dark-induced transcriptional shutdown.