Comparative analysis reveals gravity is involved in the MIZ1-regulated root hydrotropism.

Area of Science:

• Plant biology
• Plant physiology
• Developmental biology

Background:

• Hydrotropism, the directed growth of plant roots towards water, is crucial for survival.
• The interplay between hydrotropism and gravitropism (growth in response to gravity) is not well understood.

Purpose of the Study:

• To investigate the mechanisms governing the interaction between hydrotropism and gravitropism in plant roots.
• To elucidate the role of gravity in root hydrotropic responses under different water gradient orientations.

Main Methods:

• Utilized various hydrotropic systems (air, agar-sorbitol, agar-glycerol, sand) to create oblique and vertical water-potential gradients.
• Studied hydrotropism in *Arabidopsis* and tomato plants using oriented experimental setups.
• Analyzed gravitropism-deficient mutants (*aux1*, *miz1*) and a double mutant (*miz1/aux1*) to assess their hydrotropic behaviors.

Main Results:

• Gravity hindered root hydrotropism in oblique orientations but facilitated it in vertical orientations.
• The *aux1* mutant showed enhanced hydrotropism in oblique orientations but impaired vertical root growth.
• The *miz1* mutant displayed deficient hydrotropism in oblique orientations but normal vertical root growth, with the double mutant showing intermediate phenotypes.

Conclusions:

• Gravitropism plays a critical role in MIZ1-regulated root hydrotropism in both oblique and vertical orientations.
• Gravity's influence on hydrotropism depends on the orientation of the water gradient.
• This research provides new insights into how gravity shapes root water-seeking behavior.