14-3-3 Proteins in Guard Cell Signaling

International audienceGuard cells are specialized cells located at the leaf surface delimiting pores whichcontrol gas exchanges between the plant and the atmosphere. To optimize the CO$_2$uptake necessary for photosynthesis while minimizing water loss, guard cells integrateenvironmental signals to adjust stomatal aperture. The size of the stomatal pore isregulated by movements of the guard cells driven by variations in their volume andturgor. As guard cells perceive and transduce a wide array of environmental cues, theyprovide an ideal system to elucidate early events of plant signaling. Reversible proteinphosphorylation events are known to play a crucial role in the regulation of stomatalmovements. However, in some cases, phosphorylation alone is not sufficient to achievecomplete protein regulation, but is necessary to mediate the binding of interactorsthat modulate protein function. Among the phosphopeptide-binding proteins, the 14-3-3 proteins are the best characterized in plants. The 14-3-3s are found as multipleisoforms in eukaryotes and have been shown to be involved in the regulation of stomatalmovements. In this review, we describe the current knowledge about 14-3-3 roles inthe regulation of their binding partners in guard cells: receptors, ion pumps, channels,protein kinases, and some of their substrates. Regulation of these targets by 14-3-3 proteins is discussed and related to their function in guard cells during stomatalmovements in response to abiotic or biotic stresses