Newly Identified Protein Phosphatases play a vital role in regulating Protein Kinases for CO2-induced stomatal closure

Crops are highly affected by climate change. The reduction of stomatal apertures by elevated carbon dioxide affects plants in several ways. It is, therefore, crucial to identify stomatal CO2 signal transduction components that can improve crop production. Previously we showed that stomatal CO2 sensor consists of the protein complex of MPK4/12 with HT1 (Takahashi et al., 2022). At low CO2, the HT1 protein kinase phosphorylates and activates the CBC1 protein kinase, inhibiting stomatal closure. Elevated CO2 triggers interaction of MPK4 and 12 with HT1, inhibiting HT1 and CBC1 activity and leading to stomatal closure. At high CO2, a protein phosphatase (PPase) is believed to inhibit CBC1 for stomatal closure. Using infrared thermal imaging, protein phosphatase mutant is identified having cooler leaves than WT (Col0) in response to low CO2. The mutant also shows higher stomatal conductance than WT (Col0) in response to low CO2, which is consistent with infrared imaging. Blue light experiments show no difference between WT and the protein phosphatase mutant in stomatal opening, indicating that the enhanced opening of stomata in this mutant is specifically a low CO2 response and not a general stomatal opening response that would include the blue light response. Additional findings will be reported demonstrating these protein phosphatases play CO2 sensing role.