Synthesis of Acetylated Oligogalacturonide Ligands

In today`s societies with ever-growing populations, the demand for food, energy and raw materials is increasing dramatically, so there is an urgent need to increase crop productivity. The improvement of crops for the production of food, fibre and biofuels would greatly benefit from a better understanding of the plant immune system. Plants recognise and respond to attacks by pathogens using a part of the immune system that is based on the recognition of their own or foreign molecular patterns by so-called pattern recognition receptors (PRRs). These are, for example, receptor-like kinases (RLKs), which transmit danger signals to the plant when they come into contact with suitable binding partners. Despite the large number of RLKs in plants and the great abundance of glycans in the cell walls of plants, bacteria and fungi, only a handful of glycans have been found to trigger plant immune responses, and the corresponding receptors have been described for even fewer. Among the best studied of these recognised molecular patterns are oligogalacturonides (OGs), which are fragments of the plant cell wall polysaccharide pectin produced by cell wall degrading enzymes and are thought to be recognised by the so-called wall-associated kinases (WAKs) and related RLKs. Despite 30 years of research, knowledge about the exact recognition mechanism and molecular patterns preferentially bound by WAKs is still limited due to the lack of pure and well-defined oligosaccharide samples. Our aim is to determine the exact molecular structures that are recognised by their cognate receptors, such as WAKs, leading to the activation of innate immunity in plants. This will be achieved by the chemical synthesis of OGs with different lengths, oxidation states and acetylation patterns, which will subsequently enable the glycan array-based characterisation of WAKs and similar receptors. After validation with further biophysical methods, the identified oligosaccharides will be investigated for their potential to stimulate plant immune defense responses. The unique approach of combining synthetic carbohydrate chemistry with plant immunity research will enable the elucidation of advanced molecular structures with maximum capacity to trigger immune responses. The knowledge gained could enable the development of preparations made from glycan molecules to strengthen the plant immune system, perhaps one day making the use of conventional pesticides unnecessary.