# Geometric and mechanical guidance: Role of stigmatic epidermis in early pollen tube pathfinding in arabidopsis

## TL;DR

The paper explores how pollen tubes navigate in Arabidopsis by analyzing the role of the stigmatic epidermis's mechanical and geometric properties.

## Contribution

The study introduces a novel multidisciplinary approach combining biology, geometry, and mechanics to explain pollen tube guidance.

## Key findings

- Pollen tube directionality is tightly connected to the mechanical properties of stigmatic cells.
- The papilla's geometry and cell wall rigidity work together to guide pollen tubes toward the base.
- Mathematical modeling reveals that wild-type papillae impose directional guidance unlike mutant ktn1-5 cells.

## Abstract

In Arabidopsis thaliana, successful fertilisation relies on the precise guidance of the pollen tube as it navigates through the female tissues to deliver sperm cells to ovules. While prior research has focused on pistil signals directing pollen tubes towards the ovules, the pollen tube growth within the stigmatic epidermis has received limited attention. Our recent work comparing wild-type pollen tube paths on wild-type and katanin1-5 stigmatic cells, revealed a tight connection between pollen tube directionality and mechanical properties of the invaded stigmatic cell. Given that most mechanical properties of the stigmatic tissue are experimentally challenging to access, we used mathematical modelling to investigate the mechanisms underlying early pollen tube guidance through the papilla cell wall. We found that in ktn1-5, the wild-type pollen tube navigates freely across the curved papilla surface, following curves close to geodesics, whereas the wild-type papilla imposes directional guidance. The order of magnitude analysis of the mechanical forces required for pollen tubes to progress at the papilla surface indicates that both the elongated geometry of the papilla and the difference in rigidity of its cell wall layers combine to efficiently orient the pollen tube towards the papilla base.

Understanding how pollen tubes navigate within the pistil to reach their targets is a fundamental question in plant reproduction. This process begins with the intricate cell-to-cell communication initiated by the contact between the pollen grain (the carrier of male sperm cells) and the stigmatic papillae (receptive platform of the female reproductive organ). Employing a multidisciplinary approach combining methods and concepts from biology, geometry and mechanics, we explored how the growth direction of pollen tubes is influenced by the biological and physical properties of the papilla cell they invade. By comparing model predictions with experimental data, we identified a potential guidance mechanism driven by the quasi-cylindrical geometry of the papilla and the elastic properties of its cell wall.