An ANTHRANILATE SYNTHASE interacts with ABA and is required for ABA-dependent stomatal closing

Area of Science:

• Plant Biology
• Molecular Biology
• Biochemistry

Background:

• Abscisic acid (ABA) is a key phytohormone regulating plant responses to environmental stress, primarily through stomatal closure.
• While PYL/PYR/RCAR proteins are known ABA receptors, other ABA-interacting proteins are being investigated to understand ABA signaling comprehensively.
• Guard cell outward rectifying K+ channel (GORK) is one such protein implicated in ABA responses.

Purpose of the Study:

• To identify novel ABA-interacting proteins beyond the canonical PYL/PYR/RCAR family.
• To investigate the role of ANTHRANILATE SYNTHASE (ASA2) in ABA perception and signaling pathways.
• To explore the potential of ASA2 as a molecular target for improving plant stress resilience.

Main Methods:

• Identification of an ABA-interacting site in Arabidopsis thaliana ASA2, similar to that in GORK.
• Analysis of asa2 mutant plants to assess ABA-dependent stomatal closure and gene expression changes.
• Leaf transcriptomics to compare ABA-induced differentially expressed genes (DEGs) between asa2-1 and wild-type (Col-0) plants.
• Computational analysis to predict ABA interaction at the identified site.
• In vitro biochemical assays (indirect and direct) to confirm ABA-ASA2 interaction.
• Site-directed mutagenesis to study the effect of amino acid substitutions on ABA binding affinity.

Main Results:

• The asa2 mutant exhibited significant defects in ABA-induced stomatal closure.
• Transcriptomic analysis revealed reduced ABA-induced DEGs and under-representation of ABA-related terms in asa2-1 mutants, indicating decreased genomic sensitivity to ABA.
• Computational and in vitro studies confirmed specific, ligand-dependent interaction between ABA and ASA2.
• Single amino acid substitutions at the predicted ABA-binding site altered ABA affinities to varying degrees.

Conclusions:

• The study identifies ASA2 as a novel ABA-interacting protein involved in ABA-mediated stomatal closure.
• ASA2 plays a role in modulating plant sensitivity to ABA, influencing gene expression and physiological responses.
• Understanding the ABA-ASA2 interaction mechanism could lead to the development of agrochemicals for enhanced plant stress tolerance.