Models of CRK function and how they could provide specificity of stomatal aperture regulation.

(A) CRKs might act as pathway-specific or multi-pathway regulators of stomatal aperture in response to the PAMPs flg22 and chitin but also the stress hormone ABA and the abiotic stimuli O₃, darkness and CO₂. The figure has been created from data presented in Fig 10. (B) CRKs are involved in the response to pathogens downstream of extracellular ROS production. PAMPs are recognized by pattern recognition receptor complexes. Subsequently, intracellular signalling leads to activation of extracellular superoxide production by NADPH oxidases. ROS perception subsequently leads to intracellular signalling and ultimately stomatal closure. CRKs are implicated in linking extracellular ROS production to intracellular signalling and might regulate and/or interact directly with the recognition receptor complexes.