Biotic and abiotic stresses induce reactive oxygen species (ROS) production in plants as a signalling strategy. The receptor-like protein kinases (RLKs) are largely responsible for communication between cells and the extracellular environment, and ROS production is a frequent result of RLK signalling in a multitude of cellular processes (Kimura et al., 2017). However, many of the components for extracellular ROS perception, signal transmission, and specificity of downstream responses remain unknown. Cysteine-rich receptor-like kinases (CRKs) represent a subgroup of RLKs, defined by a conserved pattern of cysteines in their extracellular domain. Based on their expression profile and loss-of-function phenotypes CRKs are exciting components of ROS signalling (Wrzaczek et al., 2010; Idänheimo et al., 2014; Bourdais et al., 2 015) but based on the structure of their extracellular domain are likely not direct ROS sensors (Vaattovaara et al., 2019).
CRK2 is an evolutionarily ancient member of this protein family and a central signaling hub which can directly phosphorylate and thereby activate plasma membrane-localized NADPH oxidases (respiratory burst oxidase homologs; RBOH) in a calcium-independent manner (Kimura et al., 2019). CRK2 forms a pre-assembled complex with RBOHD to activate ROS production in response to signal perception. Interestingly, while previous research has concentrated on the N-terminal extension of RBOH proteins for the regulation of their activity, the C-terminus is also a target for protein kinases during the regulation of extracellular ROs production. Intriguingly, CRK2 also interacts with a number of different proteins to modulate callose deposition and vesicle traffic in response to biotic and abiotic stimuli (Hunter et al., 2019).
Wrzaczek M et al . 2010. BMC Plant Biol 10: 95.
Idänheimo N et al. 2014. Biochem Biophys Res Commun 445(2): 457-462.
Bourdais, et al. 2015. PLoS Genetics 7(11): e1005373.
Kimura, et al. 2017. Plant Cell 29(4): 638-654.
Hunter, et al., 2019. Plant Physiology 180(4): 2004-2021.
Kimura, et al. 2019. biorXiv doi: https://doi.org/10.1101/618819
Vaattovaara, et al. 2019. Communications
Biology 2: 56.