CO2 Signalling in Plants.

Elevated atmospheric CO2 concentrations increase the productivity of plants by enhancing the photosynthesis/photorespiration balance. It has long been recognized that CO2 acts as a signal, for example, in the regulation of stomatal closure, as well as the substrate of photosynthesis. Early concepts of CO2 signalling in plants focused on a mode of action based on alterations in primary metabolism, particularly sugar availability and signalling. However, stomatal guard cells employ a CO2 sensing and signalling mechanism that is independent of sugars. We discuss the possibility that a similar pathway exists in all cells, where it drives calcium-mediated waves of reactive oxygen species (ROS), facilitating cell-to-cell communication of biotic and abiotic threats. The plasma membrane H2O2 receptor HPCA1 is required for both stomatal closure and the systemic transmission of stress signals. Moreover, increased oxidation of the apoplast activates G protein functions and alters sugar processing and signalling in the apoplast. We discuss the concept elevated CO2 constitutes an environmental stress that has a positive effect on plant innate immunity but a negative impact on crop nutritional quality.This article is part of the theme issue 'Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the 'Resilience Revolution'?'.