A FRET sensor reports kinase activity in planta (eLIFE)

Abscisic acid (ABA) is a phytohormone involved in imparting tolerance to a variety of stress conditions. Importantly, ABA is involved in stomatal closure, mediated by the sucrose non-fermenting1-related protein kinase 2 (SnRK2) family of proteins. To report SnRK2 activity in vivo, Zhang and co-workers developed a FRET-based fluorescent sensor (named SNACs for SnRK2 activity sensor). This sensor exploits a domain from a natural substrate of SnRK2s and a 14-3-3 domain protein that responds to phosphorylation of the substrate protein. When SnRK2 phosphorylates the substrate protein,  conformation of the sensor changes to induce a Förster resonance energy transfer (FRET) between the fluorophores, resulting in fluorescence emission. The sensor reported SnRK2 activation by ABA, but high ambient CO₂ and external MeJA application failed to induce SnRK2 kinase activity, suggesting that stomatal CO₂ signaling requires basal ABA and SnRK2 signaling, but not SnRK2 activation. This report is expected to fuel development of sensors for other phosphorylation-based processes and studies to determine the pathway(s) involved in CO₂ and MeJA-induced stomatal closure.  (Summary by Pavithran Narayanan @pavi_narayanan) eLIFE 10.7554/eLife.56351