Plant cell wall patterning and expansion mediated by protein-peptide-polysaccharide interaction
Steven Moussu, Hyun Kyung Lee, Kalina T. Haas, Caroline Broyart, Ursina Rathgeb, Damien De Bellis, Thomas Levasseur, Sébastjen Schoenaers, Gorka S. Fernandez, Ueli Grossniklaus, Estelle Bonnin, Eric Hosy, Kris Vissenberg, Niko Geldner, Bernard Cathala, Herman Höfte, Julia Santiago
Abstract
Assembly of cell wall polysaccharides into specific patterns is required for plant growth. A complex of RAPID ALKALINIZATION FACTOR 4 (RALF4) and its cell wall-anchored LEUCINE-RICH REPEAT EXTENSIN 8 (LRX8)-interacting protein is crucial for cell wall integrity during pollen tube growth, but its molecular connection with the cell wall is unknown. Here, we show that LRX8-RALF4 complexes adopt a heterotetrametric configuration in vivo, displaying a dendritic distribution. The LRX8-RALF4 complex specifically interacts with demethylesterified pectins in a charge-dependent manner through RALF4's polycationic surface. The LRX8-RALF4-pectin interaction exerts a condensing effect, patterning the cell wall's polymers into a reticulated network essential for wall integrity and expansion. Our work uncovers a dual structural and signaling role for RALF4 in pollen tube growth and in the assembly of complex extracellular polymers.