How soil bacteria help plants defend themselves against disease
Source: University of Liège, 7 May 2026, amended and supplemented
Garching/Jülich/Liège, 1 July 2026. Neutron structural studies carried out using the Magnetic Reflectometer with High Incident Angle (‘MARIA’) have helped to elucidate a mechanism by which plants activate their immune defences. This mechanism differs fundamentally from the classical paradigm of immune recognition in plants: it is based on the direct interaction of a signalling molecule with the plant cell membrane, rather than with a receptor protein. The discovery opens up new avenues for the development of bio-based plant protecting agents.
Plants are not defenceless against pathogens. Certain soil bacteria, far from being mere inhabitants of the roots, send chemical signals to plants that prepare them to resist pathogens. An international research consortium, led by researchers from the University of Liège, Belgium, has just elucidated the molecular mechanism behind this immunisation. This study shows that surfactin, a cyclic lipopeptide (1) produced by bacteria of the genus Bacillus, acts not via a protein receptor, but by interacting directly with the lipids in the plant cell membrane. "Plants have sophisticated defence mechanisms against disease”, explains Marc Ongena, FNRS Research Director at the University of Liège. FRNS is the Belgian Fund for Scientific Research. "Among these, immunity induced by beneficial soil microorganisms is attracting growing interest, both in fundamental and applied research. We already knew that certain rhizosphere bacteria, particularly those of the genus Bacillus, produce cyclic lipopeptides capable of stimulating plant defences. But how these molecules were recognised by plant cells remained poorly understood until now."
The researchers focused on surfactin - one of these lipopeptides - and its interaction with Arabidopsis thaliana, a model plant commonly used in plant biology. Using a transdisciplinary approach combining cell biology, biochemistry and biophysics, they demonstrated that surfactin binds to sphingolipids (2) - and more specifically to glucosylceramide (3), present in the root cell membrane. “This interaction causes a slight remodelling of the membrane, increasing its tension, which activates mechanosensitive ion channels”, explains Magali Deleu, FNRS Senior Research Associate at the University of Liège. This triggers a signalling cascade that spreads from the roots to the leaves and prepares the plant to better resist pathogens, including the fungus Botrytis cinerea, which causes grey mould (4).
Measurements taken using the MARIA neutron reflectometer, operated by the Jülich Centre for Neutron Science (JCNS) at the Heinz Maier-Leibnitz Zentrum (FRM II) in Garching, provided evidence of minute structural changes (in the sub-nanometre range) in plant membranes when they interact with surfactin molecules. “Analysis of our data suggest both a thinning of the membrane by a few Ångström and a structural reorganisation of the upper membrane layer upon interaction with surfactin,” explains Dr Alexandros Koutsioumpas from the JCNS, MARIA instrument scientist. “Data from techniques such as SAXS, WAXS, AFM and molecular dynamics simulations complement and support the picture of a Surfactin-induced restructuring and increased membrane tension, which may activate mechanosensitive channels.”
The defence mechanism differs from the classical paradigm of plant innate immunity, in which the recognition of foreign molecules usually involves membrane protein receptors. Here, it is the physical modification of the membrane itself - rather than a lock-and-key interaction with a receptor protein - that acts as the triggering signal. This finding sheds new light on how plants can perceive their microbial environment and distinguish between beneficial bacteria and true pathogens.
In practical terms, this research forms part of efforts to develop a new generation of bio-based plant protecting agents. By understanding precisely how these bacteria or their molecules activate plant immunity, it becomes possible to envisage more targeted and effective crop protection strategies, partially replacing chemical inputs. These results thus provide a solid scientific basis for guiding the rational development of bio-based products for use in sustainable agriculture.
More information
Original publication
Gilliard, G., Pršić, J., Crowet, JM. et al.
Membrane remodelling mediates lipopeptide-induced immunity in Arabidopsis.
Nat. Plants (2026). doi.org/10.1038/s41477-026-02270-3
Glossary
(1) A cyclic lipopeptide is a small molecule produced by bacteria, consisting of a chain of amino acids closed upon itself in a ring (hence ‘cyclic’) and linked to a fatty acid chain (hence ‘lipo-’). This structure gives it properties that are both hydrophilic (affinity for water) and hydrophobic (affinity for fatty environments). Thanks to this amphiphilic nature, the molecule can interact with and insert itself into cell membranes.
(2) Sphingolipids are a family of lipids found in the cell membranes of most living organisms. They play an important structural role by contributing to the organisation and rigidity of the membrane, and are also involved in various cellular signalling functions.
(3) Glucosylceramide is a specific sphingolipid, consisting of a ceramide (a fatty molecule) to which a sugar, glucose, is attached. In plants, it is abundant in the outer leaflet of the plasma membrane and plays a key role in maintaining membrane integrity. It is this molecule that surfactin preferentially recognises in order to anchor itself in the plant membrane.
(4) Grey mould is a fungal disease of plants caused by the fungus Botrytis cinerea. It affects a very large number of cultivated species such as vines, strawberries, tomatoes and lettuce, and manifests as rapid tissue rot accompanied by a characteristic greyish mould. It is one of the most widespread and damaging diseases in agriculture and horticulture.