Functions of plant hormones and calcium signaling in regulating root hydrotropism

Hydrotropism enables plant roots to grow toward areas with high water availability. This capacity is essential for plant growth and development, particularly when water availability is a limiting factor. The physiological characterization of hydrotropism began approximately 270 years ago, and substantial progress has been made in elucidating its molecular mechanisms over the past two decades. Auxin, cytokinin, abscisic acid, brassinosteroid, and calcium have been reported by various laboratories to regulate root hydrotropism. However, the interrelation among these regulatory components in controlling root hydrotropism remains unknown. This review summarized the regulatory mechanisms of hydrotropism from the perspective of plant hormones and calcium, aiming to elucidate the internal cross-talks between their signaling pathways. Additionally, we addressed central scientific questions, provided insights into future research directions, and highlighted strategies for advancing the application of root hydrotropism in agricultural breeding.