Cutin-derived oligomers induce hallmark plant immune responses

The cuticle constitutes the outermost defensive barrier of most land plants. It comprises a polymeric matrix - cutin, surrounded by soluble waxes. Moreover, the cuticle constitutes the first line of defense against pathogen invasion, while also protecting the plant from many abiotic stresses. Aliphatic monomers in cutin have been suggested to act as immune elicitors in plants. This study analyses the potential of cutin oligomers to activate rapid signaling outputs reminiscent of pattern-triggered immunity in the model plant Arabidopsis. Cutin oligomeric mixtures led to Ca²⁺ influx and mitogen-activated protein kinase activation. Comparable responses were measured for cutin, which was also able to induce a reactive oxygen species burst. Furthermore, cutin oligomer treatment resulted in a unique transcriptional reprogramming profile, having many archetypal features of pattern-triggered immunity. Targeted spectroscopic and spectrometric analyses of the cutin oligomers suggest that the elicitor compounds consist mostly of two up to three 10,16-dihydroxyhexadecanoic acid monomers linked together through ester bonds. This study demonstrates that cutin breakdown products can act as inducers of early plant immune responses. Further investigation is needed to understand how cutin breakdowns are perceived and to explore their potential use in agriculture.