Mixed‐linked β‐1,3/1,4‐glucans derived from the cell walls of microorganisms and plants trigger disease resistance responses in plants

Plants have a very robust innate immunity system that makes infection an exception in plant/pathogen interactions. This immunity system is composed by a set of plasma membrane anchored pattern recognition receptors (PRR) present in all plant cells. These PRRs recognize microbe-associated molecular patterns (MAMPs) or molecular patterns derived from the plants (called DAMPs), that are released or synthesized during the infection process (e.g. the hydrolysis of plant cell wall). Many of these MAMP/DAMP molecules are made up of carbohydrates, such as glucose, linked by glycosidic bonds at different positions, which yields different structures. The Plant Immunity Group of the CBGP (UPM-INIA) has studied together with the company Plant Response Biotech,, a CBGP spin-off, and within the framework of an industrial Doctorate funded by Madrid’s regional government ((IND2017/BIO-7800), the capacity of some mixed glucans (MLGs), made up of glucose molecules joint by β-1,3/1,4 bonds, to activate plant immunity. In the article published in The Plant Journal, with the collaboration of a group from the Max-Planck of Germany/BOKU University of Vienna, and KTH at Stockholm , CBGP researchers describe the presence of MLGs in the cell walls of some plant pathogens (e.g. oomycetes), as it has been previously shown to be present in the cell walls of some cereals. The article reveals the simplest immune active structure of MLGs, the glucose trisaccharide MLG43 (β‐D‐cellobiosyl‐(1,3)‐β‐D‐glucose), that triggers strong immune responses in Arabidopsis thaliana plants. The responses are partially dependent on LysM PRRs CERK1, LYK4 and LYK5, that are well-known receptors/co-receptors of the fungal MAMP chitohexaose [β‐1,4‐D‐(GlcNAc)6]. However, using cross‐elicitation experiments between MLG43 and chitohexaose, the article shows that the mechanism of MLG43 and chitohexahose recognition are not identical. In collaboration with the company Plant Response, the CBGP group has shown that the preventive treatment of crops, such as tomatoes and peppers, with MLG43 provides enhanced resistance to infection by different types of pathogens (Fig. 1). These data paves the way for the future commercialization of MLGs as compounds triggering crop natural resistance to pathogens and to use these biological products to reduce the use of chemical fungicides, thus contributing to a more sustainable agriculture. In addition, the abundance of MLGs in plant wastes makes feasible to extract MLGs from these wastes and to use them to immunize other plants, contributing to circular bioeconomy. This technology is under field testing phase for its commercialization, and its use has been protected by a filled European patent.