# Loss of ASFT Enhances Drought Tolerance in Arabidopsis by Regulating OST1 Autophosphorylation

## TL;DR

This study finds that the ASFT protein negatively affects drought tolerance in Arabidopsis by inhibiting OST1 kinase activity, which controls stomatal closure.

## Contribution

The study reveals a new regulatory role for ASFT in ABA signaling through OST1 autophosphorylation modulation.

## Key findings

- ASFT interacts with and inhibits OST1 autophosphorylation, reducing stomatal aperture.
- ASFT loss increases drought tolerance in Arabidopsis, while overexpression reduces it.
- ASFT functions upstream of OST1 in ABA signaling, as confirmed by genetic evidence.

## Abstract

Drought stress severely constrains plant growth and productivity. To mitigate water loss, plants primarily regulate stomatal aperture through the Abscisic acid (ABA) signaling pathway, where the Sucrose Nonfermenting 1-Related Protein Kinase 2 (SnRK2) family kinase Open Stomata 1 (OST1) acts as a central positive regulator. However, the upstream regulators that fine-tune OST1 activity remain incompletely characterized. Aliphatic Suberin Feruloyl Transferase (ASFT), a BAHD acyltransferase essential for suberin aromatic monomer biosynthesis, was previously uncharacterized regarding its function in leaves. Here, we report that ASFT negatively regulates drought tolerance in Arabidopsis thaliana by directly interacting with OST1 and inhibiting its autophosphorylation, thereby restricting stomatal aperture. Consistent with this, the asft mutant exhibited decreased water loss and enhanced survival under drought, whereas ASFT-overexpressing lines showed opposite phenotypes. BiFC, Co-IP and in vitro kinase assays confirmed that ASFT directly interacts with OST1 and suppresses its autophosphorylation, while dehydration-induced OST1 phosphorylation was elevated in the asft mutant. Genetic evidence confirmed that ASFT functions upstream of OST1. This study reveals a moonlighting role for this suberin biosynthetic enzyme in ABA signaling and provides a potential target for breeding drought-resistant crops.