A decoy receptor derived from alternative splicing fine-tunes cytokinin signaling in Arabidopsis.

Hormone perception and signaling pathways have a fundamental regulatory function in the physiological processes of plants. Cytokinins, a class of plant hormones, regulate cell division and meristem maintenance. The cytokinin signaling pathway is well established in the model plant Arabidopsisthaliana. Several negative feedback mechanisms, tightly controlling cytokinin signaling output, have been described previously. In this study, we identified a new feedback mechanism executed through alternative splicing of the cytokinin receptor AHK4/CRE1. A novel splicing variant named CRE1^int7 results from seventh intron retention, introducing a premature termination codon in the transcript. We showed that CRE1^int7 is translated in planta into a truncated receptor lacking the C-terminal receiver domain essential for signal transduction. CRE1^int7 can bind cytokinin but cannot activate the downstream cascade. We present a novel negative feedback mechanism of the cytokinin signaling pathway, facilitated by a decoy receptor that can inactivate canonical cytokinin receptors via dimerization and compete with them for ligand binding. Ensuring proper plant growth and development requires precise control of the cytokinin signaling pathway at several levels. CRE1^int7 represents a so-far unknown mechanism for fine-tuning the cytokinin signaling pathway in Arabidopsis.