Olive fruit contains a diverse mixture of phenolic compounds that contribute to nutritional, sensory and functional traits. During ripening, verbascoside often rises as oleuropein declines, suggesting that their metabolic routes may be connected through shared precursors such as hydroxytyrosol. Translating this biochemical pattern into breeding tools is difficult. Olive has a long juvenile phase, a complex genetic background and metabolic traits controlled by interacting pathways, while quantitative trait loci can contain hundreds of genes that are difficult to prioritize. Studies in other plant species have clarified parts of verbascoside biosynthesis, but those pathways cannot simply be transferred to olive. Given these challenges, in-depth research is needed to connect phenolic variation with specific genes, regulatory steps and developmental stages in olive.
Researchers from the Institute of Biosciences and Bioresources of the National Research Council of Italy, in Perugia and Sesto Fiorentino, and the Department of Life Sciences at the University of Modena and Reggio Emilia integrated genetic, metabolic and transcriptomic evidence to dissect verbascoside biosynthesis in olive. The research article was published (DOI: 10.1093/hr/uhag154) online on April 17, 2026, in Horticulture Research. The study links variation in fruit phenolics to a major chromosome 21 locus and identifies candidate genes whose expression tracks verbascoside accumulation during fruit development.
The team first measured phenolic compounds in fruit from a Leccino × Dolce Agogia first filial generation (F1) population across two years and paired those data with an existing genetic map. Quantitative trait locus (QTL) analysis identified nine significant loci for six phenolic compounds, but verbascoside produced the strongest signal: a chromosome 21 QTL with a logarithm of odds (LOD) score of 17, explaining 75% of phenotypic variation in the progeny. The region contained 193 genes, including 47 differentially expressed genes (DEGs). The researchers then analyzed ribonucleic acid sequencing (RNA-seq) data from seven cultivars sampled at five developmental stages from 45 to 165 days after flowering (DAF), comparing high- and low-phenolic groups. Across the nine phenols, the transcriptomic analysis identified 5,344 unique DEGs, including 615 associated with verbascoside. Homology searches using 13 verified enzymes from five high-verbascoside Lamiales species yielded 249 putative olive homologs and ultimately 15 high-confidence candidate enzymes. Digital polymerase chain reaction (dPCR) validated differential expression of nine cytochrome P450 genes. Expression of OeCYP71D55 and the precursor-related OeACy3G peaked late in development, alongside maximum verbascoside accumulation. Whole-genome sequencing (WGS) analysis additionally suggested that core pathway genes are relatively conserved, with only a small subset carrying variants predicted to affect function.
The authors said the strength of the study lies in connecting a strong genetic signal with the timing of candidate-gene activity during fruit maturation. Rather than treating the chromosome 21 locus as a long list of possible genes, they said, transcriptomic and dPCR evidence helped narrow the search toward genes associated with the period of maximum verbascoside accumulation. They added that functional validation is now essential, because confirming the enzymatic roles of the leading cytochrome P450 and acyltransferase candidates will determine whether they can become dependable tools for olive improvement.
If validated, the candidate genes could be developed into markers for marker-assisted selection (MAS), allowing breeders to screen young seedlings for genetic potential before waiting years for mature trees to produce fully characterized fruit. This could shorten breeding cycles and make selection for defined phenolic profiles more precise. The study also provides a framework for testing how regulatory genes on chromosome 21 may influence enzymes located elsewhere in the genome. The authors caution, however, that high- and low-verbascoside groups were classified using metabolite measurements at 165 DAF; future work should pair transcriptomics with metabolite measurements across multiple developmental stages and functionally test leading genes in heterologous systems or edited olive cells.
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References
DOI
10.1093/hr/uhag154
Original Source URL
https://doi.org/10.1093/hr/uhag154
Funding information
This research was partially supported by OMIBREED [CUP-B93C22001440005, 2022] and REACH-XY [CUP-B93C22001920001, 2022] projects.
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, 2023. 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.