The AUX1-AFB1-CNGC14 module establishes a longitudinal root surface pH profile.

Area of Science:

• Plant biology
• Root development
• Gravitropism

Background:

• Plant roots grow via cell division and elongation, requiring apoplast acidification for cell wall extension.
• The phytohormone auxin regulates gravitropism and root development, potentially by altering apoplastic pH, but its precise role is unclear.

Purpose of the Study:

• To investigate the role of auxin in regulating the apoplastic pH gradient along the root tip.
• To elucidate the molecular mechanisms controlling root surface pH distribution.

Main Methods:

• Utilized an improved method for visualizing and quantifying root surface pH in *Arabidopsis thaliana*.
• Investigated the contribution of plasma membrane H+-ATPases (AHA) and auxin response pathways.

Main Results:

• *Arabidopsis thaliana* root surfaces exhibit distinct acidic and alkaline pH zones.
• AHA H+-ATPases are not the primary determinants of these pH zones.
• An auxin response module (AUX1, AFB1, CNCG14) rapidly controls alkaline pH in the root transition zone.

Conclusions:

• Root surface pH domains are primarily regulated by a rapid auxin response pathway, not proton pumps.
• This auxin-controlled pH regulation is essential for efficient root tip navigation.