Plants have evolved sensitive and intricate mechanisms to discriminate beneficial and harmful microorganisms via the signals that these microorganisms produce. Such signals include chitin-related molecules with huge potential for sustainable agriculture, because of their abilities to enhance plant nutrition and growth, and to incite plants to defend themselves against pests. We were pioneers in discovering the structures and roles of chitin-related molecules produced by beneficial microorganisms. Subsequently, we have developed highly sensitive biochemical methods to detect these and other chitin-related molecules, chemical and enzymatic methods to synthesise them, and molecular, genetic and biochemical tools to study how they induce their effects on plants. The project will focus on two types of chitin-related molecules produced by diverse microorganisms that all commonly interact with plants: the lipochitinoligosaccharides (LCOs) and the chitinoligosaccharides (COs). Depending on their precise chemical structures these molecules can activate the nitrogen-fixing rhizobial symbiosis, the arbuscular mycorrhizal symbiosis, plant root development and plant immunity. All types of molecule are active at extremely low concentrations, down to the nano or even to the pico molar range. With our combined expertise we aim to evaluate the extent of the spectrum of organisms capable of producing COs and LCOs, and understand the molecular mechanisms underlying the interconnections between the different responses that these molecules induce in plants. Based on this knowledge we will then treat plants with different combinations of these structurally similar, but functionally different, microbial molecular signals, and assess their effectiveness on plant growth and yield. For this we will use the model plant Medicago truncatula as a case study, followed by soybean, and perform tests in both lab conditions and field trials. Such mixes of biodegradable molecules in doses as low as a fraction of milligram per hectare will represent a breakthrough to grow crops with less fertiliser and less pesticides. The results of this ambitious new project will also lead to important fundamental discoveries in an emerging field of plant biology that seeks to understand how plants discriminate and simultaneously integrate multiple signals to produce the appropriate response.