Recovery of root hydrotropism in miz1 mutant by eliminating root gravitropism

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.

Amyloplast is involved in the MIZ1-modulated root hydrotropism

Roots exhibit hydrotropism in response to moisture gradients, with the hydrotropism-related gene Mizu-kussei1 (MIZ1) playing a role in regulating root hydrotropism in an oblique orientation. However, the mechanisms underlying MIZ1-regulated root hydrotropism are not well understood. In this study, we employed obliquely oriented experimental systems to investigate root hydrotropism in Arabidopsis. We found that the miz1 mutant displays reduced root hydrotropism but increased root gravitropism following hydrostimulation, as compared to wild-type plants. Conversely, overexpression of AtMIZ1 leads to enhanced root hydrotropism but decreased root gravitropism following hydrostimulation, as compared to wild-type plants. Using co-immunoprecipitation followed by mass spectrometry (IP-MS), we explored proteins that interact with AtMIZ1, and we identified PGMC1 co-immunoprecipitated with MIZ1 in vivo. Furthermore, the miz1 mutant exhibited higher expression of the PGMC1 gene and increased phosphoglucomutase (PGM) activity, while AtMIZ1 overexpressors resulted in lower expression of the PGMC1 gene, reduced amyloplast amount, and reduced PGM activity in comparison to wild-type roots. In addition, different Arabidopsis natural accessions having difference in their hydrotropic response demonstrated expression level of PGMC1 was negatively correlated with hydrotropic root curvature and AtMIZ1 expression. Our results provide valuable insights into the role of amyloplast in MIZ1-regulated root hydrotropism.