The CRK14 gene encoding a cysteine-rich receptor-like kinase is implicated in the regulation of global proliferative arrest in Arabidopsis thaliana.

Global proliferative arrest (GPA) is a phenomenon in monocarpic plants in which the activity of all aboveground meristems generally ceases in a nearly coordinated manner after the formation of a certain number of fruits. Despite the fact that GPA is a biologically and agriculturally important event, the underlying molecular mechanisms are not well understood. In this study, we attempted to elucidate the molecular mechanism of GPA regulation by identifying the gene responsible for the Arabidopsis mutant fireworks (fiw), causing an early GPA phenotype. Map-based cloning revealed that the fiw gene encodes CYSTEIN-RICH RECEPTOR-LIKE KINASE 14 (CRK14). Genetic analysis suggested that fiw is a missense, gain-of-function allele of CRK14. Since overexpression of the extracellular domain of CRK14 resulted in delayed GPA in the wild-type background, we concluded that CRK14 is involved in GPA regulation. Analysis of double mutants revealed that fiw acts downstream of or independently of the FRUITFULL-APETALA2 (AP2)/AP2-like pathway, which was previously reported as an age-dependent default pathway in GPA regulation. In addition, fiw is epistatic to clv with respect to GPA control. Furthermore, we found a negative effect on WUSCHEL expression in the fiw mutants. These results thus suggest the existence of a novel CRK14-dependent signaling pathway involved in GPA regulation.

A Simple Heat Treatment Increases SpCas9-Mediated Mutation Efficiency in Arabidopsis.

The CRISPR/Cas9 system is now commonly employed for genome editing in various plants such as Arabidopsis, rice and tobacco. In general, in genome editing of the Arabidopsis genome, the SpCas9 and guide RNA genes are introduced into the genome by the floral dip method. Mutations induced in the target sequence by SpCas9 are confirmed after selecting transformants by screening the T1 seed population. The advantage of this method is that genome-edited plants can be isolated easily. However, mutation efficiency in Arabidopsis using SpCas9 is not as high as that achieved in rice and tobacco, which are subjected to a tissue culture step. In this study, we compared four promoters and found that the parsley UBIQITIN promoter is highly active in Arabidopsis meristem tissue. Furthermore, we examined whether a simple heat treatment could improve mutation efficiency in Arabidopsis. Just one heat treatment at 37°C for 24 h increased the mutation efficiency at all four target sites from 3 to 42%, 43 to 62%, 54 to 75% and 89 to 91%, without detectable off-target mutations. We recommend heat treatment of plate-grown plants at 37°C for 24 h as a simple method to increase the efficiency of CRISPR/Cas9-mediated mutagenesis in Arabidopsis.