Foliar application of a geraniol nanoemulsion significantly reduced disease severity in Panax notoginseng, achieving an induced resistance efficacy of 56.3 percent against root rot. Researchers evaluated the physiological and molecular mechanisms by which this environmentally friendly immune inducer stimulates defense responses in the medicinal plant.

Root rot caused by the fungal pathogen Fusarium solani represents a major agricultural limitation that severely restricts the cultivation of Panax notoginseng. In response to foliar treatment with the geraniol nanoemulsion, plants displayed rapid early physiological defense responses characterized by the accumulation of reactive oxygen species and nitric oxide, alongside increased activity of the enzyme phenylalanine ammonia-lyase.

Transcriptomic analysis demonstrated that the geraniol nanoemulsion activated several key defense-related pathways in treated tissues. These transcriptomic responses included the activation of glutathione metabolism and the plant mitogen-activated protein kinase signaling pathway, which operate in conjunction with early biochemical reactions.

At the molecular level, the geraniol nanoemulsion specifically suppressed the expression of histone deacetylase HDA6, resulting in a global increase in histone H3 lysine 9 acetylation levels. Chromatin immunoprecipitation quantitative polymerase chain reaction confirmed significant enrichment of histone H3 lysine 9 acetylation at the promoter regions of key transcription factors in the jasmonic acid and ethylene signaling pathways and their downstream defense genes.

The enrichment of histone H3 lysine 9 acetylation correlated with transcriptional activation of the transcription factors MYC2 and ERF1 and promoted the accumulation of jasmonic acid and ethylene. Experiments utilizing exogenous hormones and pathway inhibitors confirmed that functioning jasmonic acid and ethylene signaling pathways are essential for geraniol nanoemulsion-induced disease resistance.

Genetic validation using an Arabidopsis hda6 mutant confirmed the negative regulatory role of HDA6 in plant disease resistance. The findings indicate that the geraniol nanoemulsion activates defense through two parallel branches: an HDA6-dependent epigenetic branch driving MYC2 and ERF1 transcription and hormone accumulation, and an HDA6-independent branch marked by reactive oxygen species, nitric oxide, and phenylalanine ammonia-lyase activity, offering a green control strategy for crop protection.

The authors emphasize that the induced resistance triggered by the geraniol nanoemulsion operates through at least two distinct, parallel branches rather than a single regulatory cascade. While the suppression of the histone deacetylase HDA6 constitutes an important node for epigenetic defense activation, the researchers note that it is not the exclusive pathway responsible for the observed protection against root rot in Panax notoginseng. Alongside this epigenetic mechanism, the emulsion initiates an HDA6-independent branch characterized by the rapid production of reactive oxygen species and nitric oxide, coupled with heightened phenylalanine ammonia-lyase activity. The investigation suggests that these early physiological responses likely work in concert with additional hormonal or secondary-metabolite pathways to restrict fungal disease progression.

Within the epigenetic branch, the suppression of HDA6 directly drives a global increase in histone H3 lysine 9 acetylation levels throughout the plant genome. Chromatin immunoprecipitation quantitative polymerase chain reaction assays revealed that this acetylation is significantly enriched at the promoter regions of critical defense-related transcription factors, specifically MYC2 and ERF1, as well as their corresponding downstream target genes. This targeted promoter enrichment directly correlates with the transcriptional activation of these factors, which in turn promotes the biological accumulation of both jasmonic acid and ethylene. Functional verification using exogenous hormone applications and targeted pathway inhibitors confirmed that intact jasmonic acid and ethylene signaling pathways are strictly required for the nanoemulsion to confer its 56.3 percent protective efficacy against Fusarium solani infection.

Complementing these targeted molecular analyses, broader transcriptomic profiling demonstrated that foliar administration of the nanoemulsion activates vital defense networks, including glutathione metabolism and the plant mitogen-activated protein kinase signaling pathway. Furthermore, genetic experiments using an Arabidopsis hda6 mutant confirmed that HDA6 acts as a negative regulator of disease resistance in plants. Together, these physiological and molecular findings delineate how an environmentally friendly immune inducer coordinates both chromatin remodeling and rapid biochemical defenses, offering a novel strategy for the sustainable, green control of severe root rot in Panax notoginseng cultivation.

Subject of Research: Geraniol nanoemulsion-induced resistance against Fusarium solani root rot in Panax notoginseng

Article Title: Geraniol nanoemulsion primes systemic resistance in Panax notoginseng via HDA6-mediated activation of jasmonic acid and ethylene defenses

Article References: Zhou, S.-W., Zhang, L.-Y., Cun, H.-Q., Shi, H.-M., Xu, F.-R., Noiprasert, S., Apiwongsrichai, K., Liu, X.-Y., & Dong, X. (2026). Geraniol nanoemulsion primes systemic resistance in Panax notoginseng via HDA6-mediated activation of jasmonic acid and ethylene defenses. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10322-1

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10322-1

Keywords: Panax notoginseng, geraniol nanoemulsion, Fusarium solani, root rot, HDA6, histone deacetylase, H3K9ac, jasmonic acid, ethylene, reactive oxygen species, nitric oxide, phenylalanine ammonia-lyase, MAPK signaling pathway, glutathione metabolism, MYC2, ERF1, systemic resistance, ChIP-qPCR