AFL1 is a phosphoinositide phosphate- and actin-binding protein

Area of Science:

• Plant Biology
• Molecular Plant Physiology
• Cell Biology

Background:

• At14a-Like 1 (AFL1) is a plant-specific protein induced by low water potential stress.
• Previous studies suggested AFL1 influences actin cytoskeleton dynamics and endocytic trafficking, but its direct role was unclear.

Purpose of the Study:

• To investigate the direct molecular mechanisms by which AFL1 affects actin cytoskeleton and membrane dynamics.
• To determine if AFL1 directly binds actin filaments and phosphoinositide phosphates (PIPs).

Main Methods:

• Co-sedimentation assays to test actin filament binding.
• PIP strip membrane assays to assess phosphoinositide phosphate binding.
• In vitro mutagenesis of AFL1 and analysis in transgenic plants.
• Genome editing of AFL1 and At14a in plants.

Main Results:

• AFL1 directly binds actin filaments and specific PIPs (PI(3)P, PI(5)P, PI(3,5)P2) via its C-terminal domain.
• A single amino acid mutation in the C-terminal domain abolished both actin and PIP binding in vitro and protein accumulation in planta.
• The central hydrophobic region of AFL1 is essential for its co-localization with actin filaments and the plasma membrane.
• Loss of AFL1 and At14a proteins via genome editing impaired plant growth under stress, reduced actin filament arrays, and disrupted membrane trafficking.

Conclusions:

• AFL1 directly interacts with actin filaments and PIPs, mediating its effects on cytoskeleton organization and membrane dynamics.
• These direct interactions are critical for plant acclimation and survival under low water potential stress.