Molecular Cloning and Characterization of a Gene Coding for a Putative Receptor-like Protein Kinase with a Leucine-rich Repeat Expressed in Inflorescence and Root Apices from Arabidopsis

We isolated a novel receptor-like kinase with leucine-rich repeat by a differential screening for genes that were specifically expressed in inflorescence shoot apices of Arabidopsis, and named it IRK (inflorescence and root apices receptor-like kinase) after its expression pattern and structural features. IRK contains sequentially from the amino- to carboxy-terminus: a potential signal peptide for membrane targeting, a leucine-rich repeat between two conserved cystein motifs, a transmembrane domain, and a serine/threonine kinase domain. The kinase domain expressed in E. coli showed an autophosphorylation activity in vitro, indicating that IRK encodes an active protein kinase. The IRK protein fused to green fluorescence protein was targeted to plasma membrane, indicating that IRK is a membrane-localized receptor kinase. IRK was expressed not only at shoot apices but also in root tips and developing flowers. Thus, IRK seems to be a receptor-like kinase with a relatively general function in inflorescence and root apices for an unknown signaling mechanism.