Effect of Galls on the Metabolism of Chrysanthemum Species Based on Metabolomic Profiling.

Introduction: Galls, which are abnormal or protruding tissues, form when insects bite plant cells and serve as evidence for understanding plant-insect interactions.

Objectives: This study is aimed at understanding the interactions between Chrysanthemum species and insects at the metabolomic level and to reveal the metabolic changes induced by insect galls.

Methodology: This study employed liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), along with multivariate statistics and pathway enrichment, for metabolomic profiling of Chrysanthemum glabriusculum, including gall-infected and gall-free leaves, and reported the gall phenomenon in Chrysanthemum species for the first time.

Results: LC-MS metabolomics analysis identified 105 marker metabolites, with 61 upregulated and 42 downregulated. Organic acids were the most abundant (20.00%), followed by carbohydrates (16.19%) and flavonoids (14.29%). KEGG analysis revealed significant pathway enrichment in flavone and flavonol biosynthesis, the TCA cycle, and galactose metabolism (p < 0.05). GC-MS metabolomics analysis revealed 27 volatile secondary metabolites, predominantly terpenoids (16 types), followed mainly by alcohol (4 types) and ketone compounds (three types). VIP > 1 analysis revealed 13 differentially signature metabolites; gall tissue (CgCa) presented elevated levels of β-phellandrene, camphene, and 1,8-Cineole, whereas γ-Muurolene, α-Farnesene, and Copaene were downregulated in CgCa.

Conclusions: During gall induction, C. glabriusculum plays an important role in energy metabolism through the regulation of key metabolic pathways, such as galactose metabolism and the TCA cycle, and their products; moreover, by regulating the biosynthesis of flavonoids and flavonols and the corresponding accumulation of secondary metabolites (terpenoids, ketones, and alcohols), it defends against insect-induced galls.