Date: 17th September 2025
Time: 13:00
Title: Cell-specific sensor complexes coordinate cell wall patterning and architecture to drive cell expansion
Location: Lecture room 540, Forest Sciences building, Latokartanonkaari 7
Host: Ari Pekka Mähönen
Abstract: Plant cells must coordinate their expansion with the surrounding cell wall to ensure proper growth and morphogenesis. This coordination is particularly crucial in pollen tubes, where the cell wall must counteract internal turgor pressure while maintaining an optimal elongation rate. The LRX8-RALF4 receptor complex has been identified as a key regulator of pollen tube cell wall integrity. Our work demonstrates that the LRX8-RALF4 complex physically interacts with pectin in a charge-dependent manner through a newly identified polycationic surface formed upon RALF4 binding to LRX8. Mutational disruption of this surface impairs RALF4-pectin binding, leading to defective pollen tube growth and compromised male fertility. Super-resolution and electron microscopy reveal that the LRX8-RALF4-pectin complex forms a distinct reticulated pattern in the cell wall, contributing to its overall structural integrity.
Furthermore, we show that RALF22 and root hair-specific LRX proteins, which regulate root hair expansion, fail to restore normal pollen tube growth and cell wall organization. This finding suggests that cell-specific LRX and RALF proteins have evolved to recognize and pattern distinct pectin epitopes tailored to their respective cellular contexts. Our study highlights a specialized mechanism by which pollen tube-specific sensor complexes coordinate cell wall architecture to drive targeted cellular expansion.
Julia's laboratory at the University of Lausanne—the Plant Signaling Mechanisms Laboratory—is dedicated to understanding how plants integrate structural and chemical information from their extrarllular space to regulate growth, development, and defense. We investigate how cell walls, beyond serving as static protective barriers, function as dynamic signaling platforms that sense mechanical stress and compositional changes in the extracellular matrix. A central focus of our work is to uncover the molecular mechanisms by which these extracellular signals are specifically perceived, transmitted across the plasma membrane, and relayed to intracellular compartments, ultimately reaching the nucleus to shape transcriptional and physiological responses.
By bridging processes that occur at the cell surface with downstream nuclear events, we aim to reconstruct the molecular logic of how plants coordinate environmental perception with cellular decision-making. To achieve this, we employ an integrative research strategy that combines state-of-the-art biophysics, atomic-level structural biology, advanced genetics, and cell biology approaches. This interdisciplinary framework allows us to resolve the architecture and dynamics of receptor–ligand complexes, to dissect their regulatory networks in vivo, and to connect structural and biochemical insights with functional outputs in plant development and immunity.
Ultimately, our goal is to provide a mechanistic understanding of plant cell wall signaling and remodeling networks, revealing fundamental principles of how plants adapt to an ever-changing environment while maintaining cellular integrity and growth.