Chloroplasts are at the centre of stress perception and regulation in plants. Thanks to recent work from our laboratory and others the hyperphosphorylated nucleotides guanosine pentaphosphate and tetraphosphate (ppGpp or G4P) are emerging as a major conserved signalling pathway that is capable of regulating chloroplast function to influence growth and stress acclimation in plants and algae. However, 1) what are the molecular targets of ppGpp in the chloroplast? And 2) how is ppGpp accumulation regulated? Despite recent advances these questions remain essentially unsolved, yet they are critical for understanding the molecular mechanisms of this important signalling pathway in plants. TARGET_G4P is an ambitious project that will bring together a new international consortium of partners with diverse skills and resources to address these questions using state of the art approaches. Revealing the molecular mechanisms of ppGpp signalling in plants will reinforce our understanding of ppGpp signalling in all organisms, and broaden it by uncovering novel plant-specific innovations. The knowledge generated will help us understand how plants and algae are able to cope with worsening environmental conditions, and will contribute towards improving the robustness and productivity of crop plants and algae to ensure stable and sustainable supplies of food and fuel.