# Novel small molecules disrupting polarized cell expansion and development in the moss, Physcomitrium patens

## TL;DR

This paper introduces a new molecule that disrupts tip growth in moss cells, helping to understand how polarized cell expansion is regulated.

## Contribution

The discovery of Reagent F4 as a novel small molecule that disrupts tip growth and cell polarity in Physcomitrium patens.

## Key findings

- Reagent F4 causes abnormal protonemal morphology with reduced cell elongation and expansion.
- F4 treatment leads to actin depolymerization and disruption of apical actin foci.
- F4 exposure mislocalizes ROP GTPase and downregulates lipid asymmetry-related genes.

## Abstract

Tip growth is vital for plant growth and development, yet the regulatory mechanisms governing this process remain incompletely understood. In this study, we identify Reagent F4, a novel small molecule that disrupts tip growth and polarized cell expansion in the moss, Physcomitrium patens protonemata. Through unbiased chemical screening, we found that Reagent F4 induces abnormal protonemal morphology, characterized by reduced cell elongation and stunted cell expansion. Our analyses revealed that F4 treatment triggers actin depolymerization and disrupts apical actin foci, which are critical for initiating and maintaining tip growth. Additionally, both acute and prolonged F4 exposure led to mislocalization of ROP GTPase, a key regulator of cell polarity. Transcriptomic analyses of F4 treated protonemata show significant downregulation of genes involved in lipid asymmetry, a process essential for polarized growth. These findings establish Reagent F4 as a valuable tool to investigate the molecular mechanisms governing tip growth in P. patens and highlight the potential role of lipid asymmetry in coordinating cytoskeletal organization and membrane polarity.