A role for calcium‐dependent protein kinases in differential CO<sub>2</sub>‐ and ABA‐controlled stomatal closing and low CO<sub>2</sub>‐induced stomatal opening in Arabidopsis
Sebastian Schulze, Guillaume Dubeaux, Paulo H. O. Ceciliato, Shintaro Munemasa, Maris Nuhkat, Dmitry Yarmolinsky, Jaimee Aguilar, Renee Diaz, Tamar Azoulay‐Shemer, Leonie Steinhorst, Jan Niklas Offenborn, Jörg Kudla, Hannes Kollist, Julian I. Schroeder
Abstract
Summary Low concentrations of CO 2 cause stomatal opening, whereas [CO 2 ] elevation leads to stomatal closure. Classical studies have suggested a role for Ca 2+ and protein phosphorylation in CO 2 ‐induced stomatal closing. Calcium‐dependent protein kinases (CPKs) and calcineurin‐B‐like proteins (CBLs) can sense and translate cytosolic elevation of the second messenger Ca 2+ into specific phosphorylation events. However, Ca 2+ ‐binding proteins that function in the stomatal CO 2 response remain unknown. Time‐resolved stomatal conductance measurements using intact plants, and guard cell patch‐clamp experiments were performed. We isolated cpk quintuple mutants and analyzed stomatal movements in response to CO 2 , light and abscisic acid (ABA). Interestingly, we found that cpk3/5/6/11/23 quintuple mutant plants, but not other analyzed cpk quadruple/quintuple mutants, were defective in high CO 2 ‐induced stomatal closure and, unexpectedly, also in low CO 2 ‐induced stomatal opening. Furthermore, K + ‐uptake‐channel activities were reduced in cpk3/5/6/11/23 quintuple mutants, in correlation with the stomatal opening phenotype. However, light‐mediated stomatal opening remained unaffected, and ABA responses showed slowing in some experiments. By contrast, CO 2 ‐regulated stomatal movement kinetics were not clearly affected in plasma membrane‐targeted cbl1/4/5/8/9 quintuple mutant plants. Our findings describe combinatorial cpk mutants that function in CO 2 control of stomatal movements and support the results of classical studies showing a role for Ca 2+ in this response.