Finding the balance in plant immune response: homeostasis of oligogalacturonides and cell wall damage-related immunity in plant-microbe interactions

This thesis investigates the dual roles of oligogalacturonides (OGs) and cell wall (CW) dynamics in plant immunity and development in both shoots and roots, while also exploring their interplay with root microbial communities. OGs, oligomers derived from pectin degradation, act as damage- associated molecular patterns (DAMPs), triggering immune responses likely through pattern recognition receptors (PRRs). Section I of the study investigates olive mill by-products as OG sources, discovering that OG-rich fractions, obtained by tangential flow membrane filtration of olive vegetation water, enhance plant resistance against pathogens without harming growth, thus supporting environmentally friendly pest management. Section II delves into the role of Berberine-Bridge Enzyme-like (BBE-l) proteins, particularly OGOXs, which modulate OG activity via oxidation. Findings highlight the OGOX regulatory activity of immunoeliciting OG levels, influencing resistance to various pathogens. While ogox1/2 mutants exhibit heightened resistance and accumulate active OGs, OGOX overexpression decreases resistance. Additionally, results reveal OGOXs impact broader immune signaling pathways, while OGs upregulate elements involved in epigenetic changes, including DNA demethylation. In Section III, the study highlights the roles of microbial community in modulating plant immunity in response to CW damage. It shows that roots exhibit suppressed immune responses despite OG release when commensal microbes are present. Commensal-mediated suppression of immunity related to CW-damage is mainly driven by bacteria and emerges as a predominant force within community contexts, significantly impacting root growth of Arabidopsis thaliana. Future research aims to identify bacterial strains involved in suppression of CW damage-related immunity and the microbial genetic determinants affecting plant immunity. Overall, this work elucidates the complex interplay between plant immunity, growth, and microbial interactions, presenting OG-enriched by-products as sustainable alternatives for plant protection and highlighting novel mechanisms of microbial influence on plant resilience.