Glossy onions reveal the gene behind natural insect resistance
image: Characterization of the EW and statistics of agronomic traits in onions. (A) Flowering stalks of WT (left) and GT (right). (B) SEM of WT (left) and GT (right) leaves. Scale bars = 20 mm. (C) Boxplots for comparison of WT and GT agronomic traits. The statistical significance of the difference between the GT and WT was confirmed with a Wilcoxon test. ‘*’ means P-value < 0.05, ‘***’ means P-value < 0.01, ‘NS’ means P-value ≥ 0.05. Image link: https://academic.oup.com/view-large/figure/507964877/uhaf006f1.tif
Credit: Horticulture Research
Epicuticular waxes act as a critical protective barrier for plants, shielding them from water loss, temperature stress, and insect attacks. In onions, this wax layer creates the characteristic white, glaucous surface. Traditionally, waxier plants are considered more insect-resistant because the surface reduces insect adhesion. Yet some studies show the opposite: mutants with reduced wax exhibit increased pest tolerance. The mechanisms behind this counterintuitive phenomenon remain poorly understood, especially in onions where thrips infestations severely impact yield and quality. Due to these knowledge gaps, researchers sought to uncover the genetic and physiological basis linking the glossy phenotype with thrip resistance in onions.
A collaborative research team from the Lianyungang Academy of Agricultural Sciences and Northwestern Polytechnical University published (DOI: 10.1093/hr/uhaf006) their findings on April 1, 2025, in Horticulture Research. The study identified the AcCER2 gene as the key determinant of onion leaf glossiness and thrip resistance. Using genome resequencing, transcriptomics, and metabolomics, the team demonstrated that a two-base insertion in AcCER2 causes premature protein termination, blocking very-long-chain fatty acid (VLCFA) synthesis and altering secondary metabolism. These insights shed light on how a single mutation reshapes both leaf surface traits and pest defense mechanisms.
Microscopic and chemical analyses showed that glossy-type (GT) onions lack the dense wax crystals found on wild-type (WT) leaves, resulting in smooth, shiny surfaces. Surprisingly, GT onions hosted far fewer thrips—sometimes none at all—without compromising yield or plant height. Genetic mapping pinpointed the causative mutation: a two-base “AA” insertion in AcCER2 on chromosome 6. This frameshift disrupts the CoA-acyltransferase domain, preventing fatty acid elongation from C28 to C32 and eliminating the production of 16-hentriacontanone, a major wax component. Transcriptome data revealed significant downregulation of lipid metabolism genes and upregulation of pathways related to cell wall modification and signal transduction. Metabolomic profiling showed elevated flavonoid accumulation—particularly eriodictyol-8-C-glucoside—and decreased soluble sugars like sorbose and succinic acid. The researchers propose that these metabolic shifts deter thrips by making onion tissues less palatable while simultaneously reinforcing structural defenses.
"Our findings reveal a remarkable example of genetic trade-offs in plant adaptation," said Dr. Jing Cai, corresponding author of the study. "While the AcCER2 mutation disrupts wax biosynthesis, it also reprograms multiple defense-related pathways, leading to enhanced insect resistance. This study not only identifies the key gene controlling onion leaf glossiness but also uncovers a new physiological route to pest resilience. Understanding how metabolic networks compensate for lost structural protection offers valuable clues for engineering multi-resistant crops."
This discovery opens a new avenue for onion breeding programs aimed at developing pest-resistant varieties without reliance on chemical pesticides. By leveraging the AcCER2 mutation, breeders could create onions that naturally deter thrips while maintaining normal agronomic performance. However, since wax deficiency might reduce tolerance to drought or temperature stress, future research should focus on balancing biotic and abiotic resistance. The integration of AcCER2-based selection with molecular breeding tools could accelerate the creation of climate-resilient, pest-tolerant onion cultivars—an essential step toward sustainable horticultural production and reduced pesticide use worldwide.
###
References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf006
Funding information
This study was funded by the finance special project of Lianyungang City of Jiangsu Province (No.: QNJJ2206), and the Lianyungang City No the sixth ‘521 Project’ scientific research project (No.: LYG06521202134).
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, 2024. 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.