Synthesis of Acetylated Oligogalacturonide Ligands

Wider research context: The demand of current societies, with ever-increasing populations, for food, energy, and materials grows dramatically, resulting in a clear need for increased crop productivity. Crop improvement for food, fiber, and biofuels production will greatly benefit from a more detailed understanding of plant immune function. Plants sense and respond to pathogen attacks by using an arm of the plant immune system called Pattern Triggered Immunity (PTI) that relies on the detection of exogeneous Microbe-Associated Molecular Patterns (MAMPs) and endogenous Danger-Associated Molecular Patterns (DAMPs) by Pattern-Recognition-Receptors (PRRs), such as Receptor-Like-Kinases (RLKs). The most researched DAMPs are oligogalacturonides (OGs), which are fragments of cell wall pectin produced by cell wall-degrading enzymes and are recognized by “wall-associated kinases” (WAKs) and related RLKs, such as WAK-likes (WAKLs). Despite 30 years of research, knowledge of the exact recognition mechanism and the molecular patterns preferentially bound by WAKs remains limited due to the missing availability of pure and well-defined oligosaccharide samples. Objectives: We aim at employing synthetic oligosaccharides to establish the exact size and molecular structure of oligogalacturonides (OGs) that are preferentially bound by WAKs and WAKLs and investigate their potential to activate plant immune responses. Approach: Chemical synthesis of oligogalacturonides (OGs) with different lengths, oxidation states and acetylation patterns will be performed using carefully designed galactose building blocks (BBs) in a post-assembly oxidation strategy. Particularly challenging are the formation of the exclusively -configured glycosidic bonds in oligogalacturonides (OGs) as well as developing a protecting group strategy that is compatible with acetyl groups. The oligogalacturonides (OGs) will be printed as glycan arrays for characterization of RLK-OG interactions. After hit validation in further biophysical assays, the potential of the synthetic oligogalacturonides (OGs) to stimulate or inhibit PTI responses such as ROS-production, MAP-kinase activation and defense genes induction in vivo will be investigated. Innovation: The unique approach to combine synthetic carbohydrate chemistry with plant immunity research will enable the elucidation of refined molecular structures with maximum capacity to elicit or inhibit immune responses. The generated knowledge will promote our understanding of the plant’s response to pathogenic attacks and facilitate the development of preparations of glycan molecules to boost the plant immune system, avoiding the need for using traditional pesticides.