The Arabidopsis thaliana cysteine-rich receptor-like kinases CRK6 and CRK7 protect against apoplastic oxidative stress

•Our previous study showed that CRK6 and CRK7 gene expression is induced by O3.•GUS expression is induced by O3 in CRK7::uidA transgenic plants.•crk7 is sensitive to apoplastic ROS.•Redundancy is strong between CRK6 and CRK7.•CRK6 and CRK7 are active kinases. Receptor-like kinases are important regulators of many different processes in plants. Despite their large number only a few have been functionally characterized. One of the largest subgroups of receptor-like kinases in Arabidopsis is the cysteine-rich receptor like kinases (CRKs). High sequence similarity among the CRKs has been suggested as major cause for functional redundancy. The genomic localization of CRK genes in back-to-back repeats has made their characterization through mutant analysis unpractical. Expression profiling has linked the CRKs with reactive oxygen species, important signaling molecules in plants. Here we have investigated the role of two CRKs, CRK6 and CRK7, and analyzed their role in extracellular ROS signaling. CRK6 and CRK7 are active protein kinases with differential preference for divalent cations. Our results suggest that CRK7 is involved in mediating the responses to extracellular but not chloroplastic ROS production.