A grapevine receptor reveals how chitosan activates immunity

Chitosan, a natural derivative of chitin, can alert plants to danger and is already used in crop-protection products, yet scientists have not fully understood how grapevines detect it. A new study identifies the lysin motif receptor-like kinase VvLYK4-2 as a key molecular component connecting chitosan perception with early immune signaling in grapevine. By combining cross-species complementation, targeted genome editing, defense-gene analysis, and ligand-binding experiments, the researchers found stronger binding evidence for chitosan than for chitin. The discovery helps explain why chitosan-based treatments can perform inconsistently under vineyard conditions and provides a molecular starting point for breeding grapevines that respond more reliably to bio-based disease protection.

Plants detect fragments released from microbes through pattern recognition receptors at the cell surface. Chitin, a major component of fungal cell walls, is well known to activate plant immunity, while chitosan—its deacetylated form—can both inhibit pathogens and stimulate plant defenses. Although chitosan-based products have protected grapevines against several diseases under controlled conditions, their performance in vineyards is often less consistent. This variability has limited their broader adoption, including in lower-input and organic production systems. The molecular machinery responsible for chitosan sensing also remains less clear than that for chitin. Based on these challenges, there is a need to investigate how grapevine cells perceive chitosan and convert that signal into effective immune responses.

Researchers from Université Bourgogne Europe, the French National Research Institute for Agriculture, Food and Environment (INRAE), Institut Agro, the French National Centre for Scientific Research (CNRS), Université Grenoble Alpes, and Université de Toulouse published (DOI: 10.1093/hr/uhag097) the study on March 13, 2026, in Horticulture Research. Working across three French research units, the team examined two grapevine orthologs of the Arabidopsis thaliana receptor LYK4 and found that VvLYK4-2, rather than VvLYK4-1, is the key receptor-like kinase linking chitosan recognition to immune signaling in Vitis vinifera.

The researchers first examined the expression of the grapevine genes VvLYK4-1 and VvLYK4-2 after exposure to chitin, chitosan, mites, and powdery mildew. They then introduced each gene into an Arabidopsis thaliana mutant lacking its native LYK4 and LYK5 receptors. Only VvLYK4-2 restored chitosan- and chitin-triggered mitogen-activated protein kinase (MAPK) phosphorylation and defense-gene activation across the independent transformed lines. Next, clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR–Cas9) genome editing produced three independent Chardonnay grapevine lines lacking a functional VvLYK4-2 receptor. In these mutants, chitosan no longer generated the clear MAPK response observed in wild-type plants. Real-time quantitative reverse-transcription polymerase chain reaction (RT-qPCR) analysis also showed that the defense genes VvPAL1, VvSTS1.2, VvRBOHD, and VvLOX9 failed to undergo normal induction. Chitin still triggered MAPK phosphorylation, indicating that other receptors can partly compensate for the missing receptor. In a separate Arabidopsis infection assay, expression of VvLYK4-2 restored resistance to penetration by the non-adapted grapevine powdery mildew Erysiphe necator. Finally, ligand-binding tests showed that VvLYK4-2 interacted with chitosan oligomers at lower tested concentrations than with chitin oligomers and produced a stronger chitosan-associated signal than VvLYK4-1. Together, the results identify VvLYK4-2 as a major component of chitosan-triggered immunity.

The authors said the findings clarify one of the earliest molecular steps by which grapevines recognize a promising biological defense stimulant. They said VvLYK4-2 appears to act as a gatekeeper: when the receptor is disrupted, the chitosan signal is no longer translated efficiently into kinase activation and defense-gene expression. At the same time, the remaining response to chitin shows that grapevine immunity relies on a receptor network rather than a single switch. This distinction could help explain why two closely related carbohydrate signals produce overlapping but not identical defense responses.

The work opens several routes toward more dependable biocontrol in vineyards and potentially other crops. Breeders could screen grapevine cultivars and wild Vitis relatives for natural variation in the VvLYK4-2 gene and related receptor genes, helping identify genotypes that respond strongly to chitosan-based products. Researchers could also examine whether receptor abundance changes among leaves, flowers, and developmental stages, which may help refine treatment timing and formulation. In the longer term, molecular markers associated with chitosan sensitivity could support selective breeding for plants that make better use of low-impact disease-control tools. However, the study did not test improved protection under vineyard conditions, so field trials across cultivars, environments, pathogens, and product formulations remain necessary.

###

References

DOI

10.1093/hr/uhag097

Original Source URL

https://doi.org/10.1093/hr/uhag097

Funding information

LysM-RLK phylogenetic analysis and expression profiles in Vitis vinifera challenged with different bioagressors or chitooligosaccharide elicitors.

About Horticulture Research

Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.