Stomatal CO2/bicarbonate sensor consists of two interacting protein kinases, Raf-like HT1 and non-kinase-activity activity requiring MPK12/MPK4.

The article discusses the elevated carbon dioxide (CO2) triggers interaction of the Mitogen-activated protein (MAP) kinases MPK4/MPK12 with the HT1 protein kinase, thus inhibiting HT1 kinase activity. It discusses about identifying dominant active HT1 mutants that cause insensitivity to elevated CO2; and the presented findings reveal that MPK4/12 and HT1 together constitute the long-sought primary stomatal CO2/bicarbonate sensor upstream of the CBC1 kinase in plants.