Oligogalacturonide Oxidation Modulates RALF–FERONIA Activity in Response to Cell Wall Stress

Oligogalacturonides (OGs) are galacturonic acid oligomers generated by pectin hydrolysis in the plant cell wall . They act as endogenous elicitors with signaling activity and participate in multiple developmental and defense-related processes. Oxidation of OGs by the oligogalacturonide oxidase (OGOX) enzyme abolishes their elicitor activity; however, the molecular mechanisms underlying OG perception and signal transduction remain poorly understood. Recently, Liu et al., 2024 demonstrated that OGs undergo liquid–liquid phase separation with RALF peptides, forming biomolecular condensates in the apoplast. These condensates interact with the FERONIA–LLG1 receptor complex at the plasma membrane, promoting clustering and endocytosis of a wide range of receptors. Notably, an increased abundance of oxidized OGs in the apoplast appears to inhibit this process. Here, we combined in vitro and in vivo approaches to investigate how OG oxidation affects interactions between RALF peptides and OGs, and how environmental conditions modulate these interactions. In vitro assays were used to characterize the impact of oxidation and external parameters on RALF–OG association, while in vivo imaging allowed us to analyze the dynamics of RALF–OG and RALF–oxOG condensates. We have observed that overexpression of the OGOX1 enzyme in transgenic plants reduces RALF1 signaling and compromises several FER-dependent responses to cell wall stressors, such as heat and salt. These and other findings thus far support OG oxidation status as a key determinant of RALF–FER activity, linking cell wall stress perception to downstream intracellular responses. I shall discuss results that provide new insights into the role of the RALF/FER module in OG perception and reveal how OG oxidation dampens OG biological activity by interfering with FER-mediated signaling.