A point mutation in the kinase domain of CRK10 leads to xylem vessel collapse and activation of defense responses in Arabidopsis.

Cysteine-rich receptor-like kinases (CRKs) are a large family of plasma membrane-bound receptors ubiquitous in higher plants. However, despite their prominence, their biological roles have remained largely elusive so far. In this study we report the characterisation of an Arabidopsis thaliana mutant named crk10-A397T in which alanine 397 has been substituted by a threonine in the αC-helix of the kinase domain of CRK10, known to be a crucial regulatory module of mammalian kinase activity. The crk10-A397T mutant is a dwarf which displays collapsed xylem vessels in the root and hypocotyl, whereas the vasculature of the inflorescence develops normally. In situ phosphorylation assays with 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. Transcriptomic analysis of WT and crk10-A397T mutant hypocotyls revealed that biotic and abiotic stress-responsive genes are constitutively up-regulated in the mutant, and a root-infection assay with the vascular pathogen Fusarium oxysporum demonstrated that the 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, the first such mutant to have been identified for a CRK in Arabidopsis.