Abstract
In plants, receptor-like protein kinases play essential roles in signal transduction by recognizing extracellular stimuli and activating the downstream signalling pathways. Cysteine-rich receptor-like kinases (CRKs) constitute a large subfamily of receptor-like protein kinases, with 44 members in Arabidopsis thaliana. They are distinguished by the novel C-X8-C-X2-C motif (DUF26) in the extracellular domains. One of them, CRK5, is an important component of the biochemical machinery involved in the regulation of essential physiological processes. Functional characterization of crk5 mutant plants showed their clear phenotype, manifested by impaired stomatal conductance and accelerated senescence. This phenotype correlated with accumulation of reactive oxygen species, higher foliar levels of ethylene and salicylic acid, and increased transcript abundance for genes associated with signalling pathways corresponding to these hormones. Moreover, the crk5 plants displayed enhanced cell death and oxidative damage in response to ultraviolet radiation. Complementation of CRK5 mutation managed to recover the wild-type phenotype, indicating an essential role of this gene in the regulation of growth, development, and acclimatory responses.
Highlights
A large number of receptor-like protein kinases (RLKs) evolved in plants as a response to a variety of external and internal stimuli
Previous reports showed that constitutive expression of CRK5 led to increased resistance to P.syringae and enhanced leaf growth in transgenic plants (Chen et al, 2003; Chen et al, 2004), while steroid-induced over-expression of this gene triggered hypersensitive response-like cell death (Chen et al, 2003)
In the same study, no altered phenotype was found in plants with constitutive expression of three other cysteine-rich receptor-like kinase (CRK) genes analysed (CRK6, CRK10, and CRK11), suggesting that CRK5 does not show genetic redundancy with other CRK members and appears to be an interesting candidate for the regulation of important developmental and acclimatory processes in plants
Summary
A large number of receptor-like protein kinases (RLKs) evolved in plants as a response to a variety of external and internal stimuli. RLKs bridge the gap between the perception of these stimuli and the transmission of the input signal leading to the expression of appropriate target genes. They belong to a large gene family with more than 610 members, comprising nearly 2.5% of Arabidopsis protein-coding genes (Shiu and Bleecker, 2001). A large subgroup of RLKs is constituted by cysteinerich receptor-like kinases (CRKs), with 44 members in Arabidopsis (Wrzaczek et al, 2010).
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