In order to to be successful from an individual to population level plants need to react adequately to the changing environmental conditions. Understanding how plants adapt and survive unfavourable climate conditions at the molecular level is not only of great interest from an evolutionary, ecological and environmental research perspective, but is also of great importance for practical applications. Stomata, small pores on the aerial parts of plants, control carbon dioxide (CO2) influx for photosynthesis and water vapor loss. They are surrounded by a pair of guard cells which play a central role in the regulation of plant gas-exchange so that there would be sufficient uptake of CO2 at minimal loss of water. Additionally, they serve as first barriers to air pollutants such as ozone (O3). Our research has revealed that SLAC1 anion channel plays a central role in guard cell signaling in response to various environmental factors and is responsible both for plant O3 and drought sensitivity. Additionally we have shown that activation of SLAC1 requires phosphorylation by the protein kinase OST1. However, for growth plant needs to open its stomata for CO2 fixation. This requires that SLAC1 anion channel is closed – most likely by dephosphorylation. Until now it is unknown how SLAC1 is regulated during stomatal opening. This fundamentally important question needs to be resolved for understanding basic mechanisms of plant stomatal regulation. The first aim of current project is to characterize the regulation of SLAC1 during stomatal opening Numerous components involved in guard cell signaling have been described. Still, thus far it is unknown how guard cells sense atmospheric O3 concentration changes, which eventually leads to SLAC1 activation and rapid stomatal closure. The second aim of the project is to carry out a mutant screen to identify new components in guard cell signaling from O3 perception to SLAC1 activation and rapid stomatal closure.