Arabidopsis AtADF1 is functionally affected by mutations on actin binding sites

Area of Science:

• Molecular Biology
• Plant Science
• Cell Biology

Background:

• Plant actin depolymerizing factor (ADF) proteins regulate actin dynamics by binding to actin monomers (G-actin) and filaments (F-actin).
• Understanding the specific actin-binding sites of ADFs is crucial for elucidating their roles in cellular processes.
• Arabidopsis thaliana L. AtADF1 is a key plant ADF whose functional domains require detailed investigation.

Purpose of the Study:

• To identify and characterize the critical actin-binding sites of Arabidopsis thaliana L. AtADF1.
• To investigate the in vitro and in vivo functions of AtADF1 mutants with altered actin-binding affinities.
• To determine the role of G-actin binding versus F-actin binding in AtADF1's regulation of actin organization and plant development.

Main Methods:

• Site-directed mutagenesis was used to generate AtADF1 mutants with specific amino acid substitutions.
• In vitro biochemical assays were performed to assess the binding affinities of mutant AtADF1 proteins to G- and F-actin.
• Transient expression in onion epidermal cells and stable expression in transgenic Arabidopsis thaliana L. plants were used to analyze mutant protein function in vivo, focusing on actin organization and seedling growth.

Main Results:

• Charged residues (Arg98, Lys100) in α-helix 3 and the N-terminus form an essential binding site for both G- and F-actin.
• Basic residues in β-strand 5 (K82) and α-helix 4 (R135, R137) constitute another binding site important for F-actin interaction.
• Mutants with reduced F-actin binding affinity remained functional if G-actin binding was preserved, highlighting the essential role of G-actin interaction for ADF function.

Conclusions:

• Specific charged and basic residues in AtADF1 define distinct actin-binding sites critical for its function.
• G-actin binding activity is indispensable for AtADF1's role in actin depolymerization and the overall control of actin organization.
• The study provides insights into how ADF mutations affect actin dynamics, influencing plant cell structure and seedling development.