A point mutation in the kinase domain of CRK10 leads to xylem vessel collapse and activates defence responses

Cysteine-rich receptor-like kinases (CRKs) are a large family of plasma membrane-bound receptors ubiquitous in higher plants. They are transcriptionally regulated by a wide variety of environmental cues and stresses, however their precise biological roles remain largely unknown. Here we report a novel mutant isolated for the CYSTEINE-RICH RECEPTOR-LIKE KINASE 10 (CRK10) of Arabidopsis thaliana which harbours the substitution of alanine 397 by a threonine in the C-helix of its kinase domain and which we registered as crk10-A397T in the community database. In situ phosphorylation assays with the His-tagged wild type (WT) and crk10-A397T versions of the CRK10 kinase domain revealed that both alleles are active kinases capable of auto-phosphorylation with the newly introduced threonine acting as an additional phosphorylation site in crk10-A397T. Phenotypically the mutant is a dwarf and the analysis of thin cross sections with light and transmission electron microscopy revealed that collapsed xylem vessels in roots and hypocotyls are very likely the cause for this reduction in stature. Transcriptomic analysis of WT and mutant hypocotyls revealed that predominantly biotic and abiotic stress-responsive genes are constitutively up-regulated in the mutant. Root-infection assays with the vascular pathogen Fusarium oxysporum demonstrated that the crk10-A397T mutant has enhanced resistance to this pathogen compared to WT plants. Taken together our results suggest that crk10-A397T is a gain-of-function allele of CRK10 and open up new avenues for the investigation of this elusive receptor-like kinase family.