# Proximity labelling suggests association of the nonhost receptor PSS1 protein with enzymes of multiple defense pathways in Arabidopsis

## TL;DR

This study explores how a plant protein called PSS1 interacts with other proteins to help Arabidopsis resist soybean pathogens.

## Contribution

The study identifies new protein associations of PSS1 using proximity labeling, suggesting roles in multiple defense pathways.

## Key findings

- PSS1 is associated with plasma membrane H(+)-ATPase 6 before infection but not after.
- PSS1 interacts with TGG1 and LIN2, enzymes involved in defense-related metabolism and ROS production.
- PSS1-associated proteins are localized in plastid and cytosol, suggesting redistribution during infection.

## Abstract

PSS1 encoding a glycine-rich integral plasma membrane protein plays a pivotal role in nonhost resistance of Arabidopsis against the soybean pathogens, Phytophthora sojae and Fusarium virguliforme. Notably, P. sojae fails to penetrate the wildtype Col-0 ecotype but not the pss1 mutant. To elucidate the molecular basis of PSS1-mediated nonhost immunity, we employed a miniTurbo-based proximity labeling approach.

The miniTurbo fused to either wild-type PSS1 or its mutant variant, PSS1G119D, and expressed in the pss1 knockout mutant background. Seedlings were challenged with or without P. sojae zoospores and biotinylated proteins were isolated for mass spectrometry analysis. Col-0 and PSS1G119D lines served as controls to validate labeling specificity and biological relevance.

Prior to infection, spatial proximity between PSS1 and the plasma membrane H(+)-ATPase 6 transporter was detected; however, this association was not observed following P. sojae challenge. Several candidate PSS1-associated proteins were predominantly localized to the plastid and cytosol, suggesting a possible redistribution of PSS1 during infection, potentially to facilitate nonhost immunity. PSS1 is also associated with thioglucoside glucohydrolase 1 (TGG1), a key enzyme in glucosinolate (GLS) metabolism, and to coproporphyrinogen III oxidase (LIN2), involved in tetrapyrrole biosynthesis and reactive oxygen species (ROS) production linked to defense-related cell death.

We hypothesize that PSS1 contributes to a positive feedback loop that enhances multiple defense pathways. Based on consistent enrichment and functional relevance, we nominate TGG1, LIN2, and H(+)-ATPase 6 as priority candidates for functional validation in the context of PSS1-mediated nonhost immunity.