Guanosine tetraphosphate (ppGpp) promotes tolerance to 2 excess light in Arabidopsis thaliana.

Abstract

Guanosine tetraphosphate (ppGpp) is a hyperphosphorylated nucleotide originally discovered in prokaryotes and found in the chloroplasts of plants and algae. In plants, ppGpp regulates photosynthetic activity, which is important in acclimation to environmental stresses such as nitrogen limitation. However, the full range of stresses involving ppGpp signalling is not yet known. Here, we investigated the role of ppGpp accumulation in the acclimation of plants to excess light. We found that the over-accumulation of ppGpp in transgenic lines that overexpress RSH3 (OX:RSH3) increases tolerance to excess light. Although ppGpp leads to higher non-photochemical energy dissipation (NPQ) than in wild-type plants, we show that NPQ is not critical for the enhanced excess light tolerance. Rather, our results show that ppGpp accumulation leads to broad changes in plant physiology that prime plants to resist and subsequently recover from excess light exposure. ppGpp levels themselves also increase in response to excess light exposure, suggesting that ppGpp may play a physiological role in excess light acclimation. Our work adds to a growing body of evidence for the importance of ppGpp in plant stress acclimation.