MIZU-KUSSEI 1 regulates root hydrotropism and cytokinin signal transduction by interacting with cytokinin receptors.

This article focuses on the role of MIZU-KUSSEI 1 (MIZ1) in regulating cytokinin signal transduction essential for root hydrotropism in Arabidopsis thaliana. The study demonstrates that MIZ1 physically interacts with cytokinin receptors known as ARABIDOPSIS HISTIDINE KINASEs (AHKs) to modulate the expression of Type-A ARABIDOPSIS RESPONSE REGULATORS (ARRs), specifically ARR16 and ARR17, thereby influencing cytokinin sensitivity and root growth toward moisture gradients. Mutants deficient in MIZ1, AHKs, or multiple ARRs exhibit impaired hydrotropic responses, indicating the critical involvement of cytokinin signaling in this process. Additionally, MIZ1 regulates cytokinin homeostasis by controlling genes involved in cytokinin biosynthesis and catabolism, further supporting its central role in root adaptation to drought stress.