Is floral scent determined only by the enzymes that make scent compounds? Cells also have mechanisms that regulate how much the instructions for making enzymes are used. A 2025 study by Wang and colleagues examined the white-flowered ginger-family plant Hedychium coronarium and showed that very short RNAs are involved in scent production.
The focus of the study was microRNAs. Rather than serving as scent ingredients, these small molecules regulate the activity of other genes. Starting with changes in scent compounds during flower development, the researchers experimentally followed candidate microRNAs and their targets.
Examining buds, fully open flowers, and senescent flowers
The plant studied was Hedychium coronarium, known for its strong floral fragrance. The researchers compared flowers grown in a greenhouse in Guangzhou, China, at three stages: buds, full bloom, and senescence. Gas chromatography–mass spectrometry of compounds volatilizing from the flowers identified ocimene, linalool, and eucalyptol as major constituents.
Emissions of these compounds increased as the flowers opened, were high at full bloom, and declined somewhat during senescence. However, these were changes in compounds measured by instruments. The experiments did not assess how intense or pleasant people perceived the fragrance to be.
Analysis of small RNAs in petals at the same three stages identified 171 known microRNAs and 32 new candidates. A method examining fragments of cleaved RNA also identified 102 cleavage sites corresponding to 90 target genes. This did not establish that all were scent-specific genes; it was a broad search to narrow down candidates for detailed investigation.
The instructions for making scent also have regulators
Genetic information is first copied into messenger RNA, which is then used to make proteins. MicroRNAs act on specific messenger RNAs, contributing to their degradation or suppressing protein production. Thus, even without directly making scent compounds, they may change how the machinery for scent production operates.
The researchers focused on two microRNAs, miR167n and miR393a. Their abundance changed in a pattern similar to scent compound emissions during flower development. Meanwhile, the candidate targets HcARF8 and HcTIR1 generally showed the opposite pattern of activity. Both belong to signaling machinery associated with the plant hormone auxin.
At this stage, the evidence was an association between changes in abundance. The researchers therefore temporarily introduced the candidate combinations into tobacco leaves and tested them using fluorescence as a marker. Fluorescence decreased when the corresponding microRNA was active at the same time, supporting the relationships in which miR167n targets HcARF8 and miR393a targets HcTIR1.
Weakening the small RNAs changed the compounds
Next, they interfered with the activity of each of the two microRNAs in Hedychium flowers. Several scent compounds, including ocimene and linalool, decreased relative to controls. Because intervention in molecular activity changed the scent compounds, rather than the evidence being purely observational, the authors consider these two microRNAs to be involved in promoting scent metabolism.
Conversely, experiments weakening the targets HcARF8 or HcTIR1 increased linalool. However, eucalyptol and some other compounds decreased. The relationship is therefore not as simple as saying that weakening these genes increases all floral fragrance. The effects of regulation differ among compounds.
In experiments applying auxin externally, ocimene and some other compounds and the two microRNAs increased, while methyl benzoate decreased. Treatment that interfered with auxin action reduced several scent compounds. These findings offer clues linking plant hormone signals and small RNAs to fragrance production.
One pathway leading to a biosynthetic enzyme
The researchers examined HcARF8, the target of miR167n, in greater detail. HcARF8 is a protein that regulates how actively another gene is used. They investigated its relationship with HcTPS8, a gene encoding an enzyme known to be involved in linalool synthesis.
A yeast-based binding assay indicated that HcARF8 binds to the HcTPS8 promoter. A promoter is a DNA region involved in regulating how much information is read from a gene. A luminescence-based experiment in tobacco leaves also showed that adding HcARF8 suppressed activity mediated by this region.
These results support a pathway in which a small RNA acts on a regulator that suppresses scent biosynthesis. Following the regulation upstream of the enzymes that produce scent compounds helps reveal how their amounts change.
The original paper contains both a Results description in which HcARF8 suppresses HcTPS8 and a Discussion description in which it activates HcTPS8. The suppression described here follows the direction indicated by the Results explanation and the luminescence assay figure. Not all regulatory relationships have yet been established without inconsistency.
Basic research toward scent improvement
An important perspective offered by the authors is to view floral scent not as a matter of enzymes alone, but as a system involving small RNAs, target genes, and plant hormone signals. These regulatory points could offer clues for future breeding to alter the accumulation or composition of scent compounds.
However, these were molecular experiments centered on a particular greenhouse-grown plant. RNA analyses used three replicates per stage, and some binding and regulatory experiments used yeast or tobacco. Many predicted targets remain functionally untested, and the results of short-term gene suppression do not necessarily translate into stable traits in a new cultivar.
The authors identify a need to investigate interactions with other genes and plant hormones, together with environmental conditions such as temperature, humidity, and light. Increasing a compound and making a fragrance more pleasing to people are also separate questions.
Summary
Manipulating two microRNAs and their targets in Hedychium flowers changed several scent compounds. For one of these pathways, the researchers were able to trace the mechanism to a regulator that binds to a scent biosynthetic enzyme gene.
Floral scent is shaped not only by enzymes converting raw materials, but also by regulation of which instructions are used and to what extent. Understanding this machinery, including small RNAs, provides a foundation for understanding why flowers change their scent as they develop or their environment changes, and for considering future scent improvement.
References
Wang, F., Liu, L., Yu, R., Li, X., Yu, Y., Li, X., Yue, Y., & Fan, Y. (2025). Function of floral fragrance-related microRNAs and their targets in Hedychium coronarium. BMC Genomics, 26, 430. DOI: 10.1186/s12864-025-11583-0 / Full original article. Original article: © The Author(s) 2025, CC BY-NC-ND 4.0.
