The natural chalcone derivative 4‐hydroxychalcone primes tobacco immunity against TMV via Ca 2+ ‐ ROS signaling and flavonoid biosynthesis

Abstract BACKGROUND Tobacco mosaic virus (TMV) threatens global agriculture due to environmental persistence and limited chemical controls. Plant immune elicitors offer promising solutions, yet novel low‐cost agents are urgently needed. RESULTS Here, natural chalcones, particularly 4‐hydroxychalcone (4‐HC), demonstrated potent anti‐TMV activity as plant immune elicitors. Among eight chalcones screened, 4‐HC at 1 m m achieved 48.36% protective efficacy – comparable to the benchmark elicitor benzothiazole (BTH). Crucially, 4‐HC showed no direct virucidal activity against TMV particles (confirmed by half‐leaf assays and transmission electron microscopy (TEM)), indicating plant‐mediated defense induction. Transcriptomics revealed 4‐HC significantly up‐regulated immune pathways, including plant–pathogen interactions, mitogen‐activated protein kinase (MAPK) signaling ( MPK4 , MKK5 ), and WRKY transcription factors. Mechanistically, 4‐HC elicited rapid calcium ion (Ca 2+ ) flux and sustained reactive oxygen species (ROS) burst (four‐fold hydrogen peroxide (H 2 O 2 ) increase at 24 h), enhancing defense‐related enzyme activities (phenylalanine ammonia‐lyase (PAL), peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT)) to establish systemic resistance. It also promoted flavonoid accumulation (two‐fold at 72 h), leveraging its role as a flavonoid precursor. CONCLUSION This study identifies 4‐HC as a sustainable, plant‐derived immune elicitor that primes tobacco immunity against TMV through conserved signaling cascades, highlighting its potential for eco‐friendly disease management. © 2025 Society of Chemical Industry.