Can signals traveling within a plant also change how much fragrance its flowers produce? A 2025 study by Wang and colleagues linked the plant hormone salicylic acid to the machinery that produces a particular scent compound in a chrysanthemum cultivar with a fruity fragrance.
Salicylic acid is a signaling substance involved in plant growth and responses to disease, among other processes. The researchers wanted to know whether this signal also reaches floral scent biosynthesis and, if so, which genes and proteins it acts through.
- Following changes in scent compounds in one chrysanthemum
- Testing the enzyme that makes the scent compound
- Two regulators that suppress synthesis
- The salicylic acid signal passes through this combination
- Production and release need not happen at the same time
- The connection between defense and scent remains to be explored
- Summary
- References
Following changes in scent compounds in one chrysanthemum
The researchers studied the cultivated chrysanthemum variety “Xiaokuixiang.” They compared three stages, buds, early flowering, and full bloom, as well as four parts of the flower head: the outer florets that look like petals, the central florets, the involucral bracts surrounding the buds, and the receptacle supporting the flower head.
They placed cut flowers in containers, collected volatile compounds, and analyzed them by gas chromatography–mass spectrometry, detecting 24 terpenes. One of the most abundant was (E)-β-farnesene. Terpenes are a family of compounds that includes many plant scent constituents.
The measured amount of (E)-β-farnesene increased as the flowers developed, reaching its highest level at full bloom. Among the different parts, it was abundant in the involucral bracts and receptacles, and was also found in glandular trichomes, small secretory structures on the surface.
However, the most abundant compound detected is not necessarily the one people perceive most strongly. This study followed the production of a compound abundant in this cultivar; it did not assess the overall pleasantness of chrysanthemum fragrance or a mechanism shared by all chrysanthemums.
Testing the enzyme that makes the scent compound
First, the researchers sought candidate enzymes that produce (E)-β-farnesene. They narrowed the candidates through a broad analysis of gene activity and examined a gene they named CmEβFS in detail.
When they prepared and tested the protein encoded by this gene, it produced (E)-β-farnesene from the precursor farnesyl diphosphate. Furthermore, reducing the gene’s activity in chrysanthemum decreased the amount of the compound. Beyond an inference based on sequence similarity, they verified its actual production capability and its role in the plant.
The next question was what controls how much of this biosynthetic enzyme is made. They examined how much information was being read from genes and looked for upstream regulators.
Two regulators that suppress synthesis
They identified a protein called CmWRKY1. It is a type of transcription factor, a protein that binds to specific DNA regions and regulates the reading of genes. Binding experiments and experiments that used luminescence to measure the level of gene readout showed that it suppresses the gene encoding the biosynthetic enzyme.
When this regulator was weakened in chrysanthemum, activity of the biosynthetic enzyme gene and the amount of (E)-β-farnesene increased. In other words, weakening a regulator that suppresses synthesis increased the compound.
The researchers also identified CmNPR3, a protein involved in salicylic acid perception, as a partner that binds to this regulator. They confirmed the interaction through several binding assays and showed that the two proteins working together strengthened suppression of the biosynthetic enzyme gene.
Chrysanthemums with reduced CmNPR3 activity also showed increased activity of the biosynthetic enzyme gene and higher amounts of the compound. The proposed mechanism thus combines a DNA-binding regulator with a partner involved in hormonal signaling to regulate scent compound production.
The salicylic acid signal passes through this combination
Applying salicylic acid to flowers of unmodified chrysanthemums increased the activity of the two regulator genes and decreased both the activity of the biosynthetic enzyme gene and the amount of (E)-β-farnesene. The researchers investigated not only whether the hormone and scent compound changed together, but also whether the regulators mediated the effect.
In plants in which either of the two regulators was weakened individually, salicylic acid still reduced the compound. In contrast, in plants with both regulators weakened simultaneously, salicylic acid treatment did not significantly change the activity of the biosynthetic enzyme gene or the amount of the compound.
From these results, the authors concluded that the CmWRKY1–CmNPR3 combination mediates at least part of the regulation by salicylic acid. The central finding is a specific pathway linking an internal plant signal to an enzyme that produces scent.
Production and release need not happen at the same time
Interestingly, while the amount of the compound increased toward full bloom, the biosynthetic enzyme gene was highly active in buds. The authors proposed that the compound is made during the bud stage and released later as glandular trichomes mature or rupture.
Electron microscopy showed more ruptured glandular trichomes at full bloom. By distinguishing compound accumulation from the mechanisms of synthesis and release, the authors sought to explain the time lag between gene activity and the measured amount of the compound.
However, the experiments did not continuously track when individual compounds were made and when they were released. Volatile analysis was also performed on cut samples in heated containers. These measurements do not directly represent emissions from living flowers under natural conditions or the intensity perceived by people.
The connection between defense and scent remains to be explored
Salicylic acid is involved in plant defense, and (E)-β-farnesene is also known as an aphid alarm substance. The authors suggest that the regulatory pathway identified here may be involved in responses to insect pests and relationships with pollinators.
However, this study did not test pest resistance or pollinator attraction. Further work is needed to establish what benefits increasing or decreasing the compound might bring to plant defense or reproduction. Regulation of a scent compound cannot simply be described as an insect-repellent effect.
The main quantitative experiments used three biological replicates, with some measurements using a single flower and others pooling several flowers. This is basic research on a particular cultivar under particular growing conditions, and the authors note that the effects of salicylic acid may differ with plant species and concentration.
Summary
In one chrysanthemum cultivar, salicylic acid-related signaling and two regulatory proteins were linked to a mechanism that suppresses the enzyme responsible for (E)-β-farnesene synthesis. Scent production is connected not only to enzymes but also to the plant signaling systems that control their activity.
Understanding this pathway offers clues for scent improvement and a step toward understanding how plants coordinate growth- and defense-related signals with fragrance production. Separately tracking production, storage, and release is also important for interpreting changes in floral scent.
References
Wang, Z., Yuan, Y., Dong, R., Zeng, R., Zhao, X., Xu, Y., Gao, J., Hong, B., & Gu, Z. (2025). Salicylic acid regulates biosynthesis of floral fragrance (E)-β-farnesene via NPR3-WRKY1 module in chrysanthemum. Molecular Horticulture, 5, 52. DOI: 10.1186/s43897-025-00174-y / Full original article. Original article: © The Author(s) 2025, CC BY 4.0.
