Guard cells: Finding a MATE

Nature Commun. 6, 6057 (2015)

Stomatal pores allow gas exchange between plant leaves and their environment. They open to allow entry of carbon dioxide for photosynthesis, and close to prevent excessive water loss. Wang Tian and Congcong Hou, of the Capital Normal University, Beijing, and colleagues, describe how elevated CO₂ concentration is perceived in the guard cells that surround the pore and how this triggers stomatal closure.

Using a genetic screen in Arabidopsis, the authors identified the gene RESISTANT TO HIGH CO2 1 (RHC1), required for stomatal closure in response to high CO₂ concentration. RHC1 encodes a multi-antimicrobial extrusion (MATE) protein that interacts with carbonic anhydrase in guard cells. Carbonic anhydrase converts CO₂ to bicarbonate thus linking CO₂ levels to the guard-cell signalling pathway. RHC1 also represses the activity of HT1, a kinase that negatively regulates the CO₂ response. This relieves HT1-mediated inactivation of OST1, a positive regulator of SLAC1 ion channels, whose activity mediates changes in guard-cell turgor. By heterologous expression of these components in frog oocytes, the authors are able to reconstitute the core molecular pathway that links perception of CO₂ to ion-channel activity.

These findings trace a pathway by which increasing CO₂ in the atmosphere can influence stomatal aperture and gas exchange in plants, thereby connecting photosynthesis to the control of water availability.