Abstract text: In plants, the cell wall is a critical growth regulator with its ever-changing composition and structure. Indeed, the cell wall is rigid to effectively withstand turgor pressure, and plastic to allow for cell growth. These ambivalent properties are dynamic during growth. To better understand these dynamic properties, one must investigate cell wall architecture. The cell wall is mainly composed of polysaccharides, along with structural proteins like EXTENSINs (EXTs). These proteins are HRGPs (Hydroxyproline Rich GlycoProteins) with the unique ability to self-assemble covalently, forming a macromolecular glycoprotein network. Recently, EXTs have been shown to be crucial for root hair elongation, some ext mutants having drastically shorter root hairs.

Through biochemical approaches, we investigated how EXTs interact with each other to build the EXT network. To reach this goal, we produced root hair-specific recombinant EXTs. Using these proteins, we explored EXTENSIN network formation determinants in vitro. We demonstrated the importance of EXT-EXT hydrophobic interactions as a first-step prior to covalent network formation. Indeed, when hydrophobic bonds are disrupted, EXTENSINs can no longer form di-isodityrosine covalent bonds. Altogether, this project expands our understanding of the dynamic formation a cell wall macromolecular network required for plant cell growth.