Floral volatile terpenoids (FVTs) belong to a group of volatile organic compounds (VOC) that play important roles in attracting pollinators, defending against pathogens and parasites and serving as signals associated with biotic and abiotic stress responses. Although research on FVTs has been increasing, a systematic generalization is lacking. Among flowering plants used mainly for ornamental purposes, a systematic study on the production of FVTs in flowers with characteristic aromas is still limited. This paper reviews the biological functions and biosynthesis of FVTs, which may contribute a foundational aspect for future research. We highlight regulatory mechanisms that control the production of FVTs in ornamental flowers and the intersection of biosynthetic pathways that produce flower fragrance and color. Additionally, we summarize the opportunities and challenges facing FVT research in the whole genome and -omics eras and the possible research directions that will provide a foundation for further innovation and utilization of flowering ornamental plants and their germplasm resources.

The v-MYB avivan myoblastsis virus oncogene homolog (MYB) family is the largest gene family of the transcription factor in plants, involved in plant growth and development, secondary metabolism and resistance to biotic/abiotic stress. Antirrhinum majus (snapdragon) is an ideal material for studying ornamental traits. Nevertheless, there has been no systematic investigation into the AmMYB family of snapdragons. In this study, we identified a total of 162 members of the AmMYB gene family in snapdragons. Gene structure analysis showed that the AmMYB family within the same subgroup had a similar structure and motifs. Analysis of gene duplication events revealed that the amplification of the AmMYB family was driven by whole-genome duplication (WGD) and dispersed duplication. The analysis of cis-acting elements in the promoter region of AmMYB genes reveals a collaborative involvement of light-responsive growth and development elements, stress resistance elements, and hormone-responsive elements jointly participating in the regulation of the AmMYB gene. Collinearity analysis demonstrates significant functional distinctions between AmMYB and monocotyledonous plants. The classification of AmMYB members results in 3 main subgroups with 36 smaller subgroups. All AmMYB genes are distributed across all eight chromosomes, with no apparent correlation between subfamily distribution and chromosome length. Through phylogenetic analysis and RNA-seq analysis, we have identified 9 R2R3-MYB genes that potentially play a role in the regulation of floral volatile organic compounds (FVOCs) biosynthesis. Their expression patterns were verified by qRT-PCR experiments. This study establishes a robust foundation for further investigations into the functionality of AmMYB genes and their molecular mechanisms underlying FVOC biosynthesis in snapdragons.

Geranyl diphosphate synthase (GPPS) is a key enzyme in the plant isoprenoid metabolic pathway and regulates the biosynthesis of volatile monoterpenes. It plays an important role in the biosynthesis of floral volatile terpenoids (FVTs) and inter-cultivar variation in snapdragon. Despite its importance in floral scent formation, the GPPS/GGPPS gene family in snapdragon (Antirrhinum majus L.) has not been systematically characterized. In this study, nine GPPS/GGPPS family members were identified at genome-wide level. These include six AmGPPS and three AmGGPPS genes. Phylogenetic analysis grouped them into distinct subfamilies. We further analyzed their chromosomal locations, gene structures, conserved protein motifs, and promoter cis-acting elements. These results revealed both conservation and functional divergence within the gene family. To explore their functional roles, we compared gene expression profiles at the full flowering stage. This comparison was performed between strongly scented cultivar (Am3) and the weakly scented cultivar (Am5). Among all candidates, AmGPPS6 showed the most significant differential expression. Further, functional validation was conducted using transient overexpression and virus-induced gene silencing (VIGS). Overexpression of AmGPPS6 significantly increased terpenoid production. Total floral volatile terpenoids (FVTs) increased by 1.4 fold. Both monoterpene and sesquiterpene emissions were enhanced. In contrast, silencing of AmGPPS6 markedly reduced the emission of key monoterpenes such as ocimene and its isomers. Sequence analysis showed that AmGPPS6 shares 67.04% identity with canonical GPPS small subunit (GPPS.SSU). However, it lacks the conserved catalytic DDx2-D motif. This suggests that AmGGPPS2 is not catalytically active. Instead, it likely functions through heterodimer with AmGGPPS2. This interaction is supported by coordinated transcriptional expression patterns. Additionally, natural sequence polymorphisms were identified in GPPS.SSU. These variations, rather than those in GPPS.LSU, appear to drive differences in monoterpense emission between cultivars. In conclusion, AmGPPS6 in a key regulator of floral scent biosynthesis in snapdragon. This study provides new insights into functional roles of GPPS/GGPPS genes. It also offers valuable gene targets for the molecular breeding of aromatic traits in ornamental plants.