Decoy Receptor Fine-tunes Cytokinin Signaling in Arabidopsis

David Zalabák (Palacký University in Olomouc, Czech Republic): The plant hormone cytokinin plays a vital role in plant growth and development. While the molecular mechanism of cytokinin signal perception and transduction is well described, regulating this cascade in planta seems more ambiguous. The Histidine kinase receptor CRE1 (CYTOKININ RESPONSE 1)/AHK4 (ARABIDOPSIS HISTIDINE KINASE 4)/WOL (WOODEN LEG), is the crucial element of the cytokinin signaling cascade in Arabidopsis. The cytokinin-signaling pathway is under stringent negative feedback control executed at several levels. In this study, we have discovered a novel CRE1 transcript variant with a negative feedback regulatory function. Cytokinin application induces intron retention within the CRE1 transcript, introducing a premature termination codon. The resulting transcript encodes for a truncated receptor lacking the receiver domain essential for activating the cascade. Our results demonstrate that the truncated receptor acts as a decoy competing for ligand binding with the canonical CRE1 receptors, ultimately leading to an attenuation of cytokinin signaling. Thus, we propose a novel regulatory mechanism of cytokinin perception mediated by alternative splicing of CRE1 receptors.