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

Abstract

Hormone perception and signaling pathways play a fundamental regulatory function in the physiological processes of plants. Cytokinins, plant hormones, regulate cell division and meristem maintenance. The cytokinin signaling pathway is well-established in model plant Arabidopsis. Several negative feedback mechanisms, tightly controlling the cytokinin signaling output, were described previously. Here, we identified a new feedback mechanism executed through an 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 show that CRE1^int7 is translated in planta into a truncated receptor lacking the C-terminal receiver domain essential for signal transduction. The CRE1^int7 can bind the cytokinin but cannot activate the downstream cascade. We present a novel negative feedback mechanism of the cytokinin signaling pathway facilitated by a decoy receptor, which can inactivate canonical cytokinin receptors via dimerization and compete with them for ligand binding. While a similar molecular mechanism is well-known in mammals, decoy receptors are rare in plants. Ensuring proper plant growth and development requires precise control of the cytokinin signaling pathway at several levels. The CRE1^int7 represents a yet unknown mechanism for fine-tuning the cytokinin signaling pathway in Arabidopsis.