Background: To reveal the key genes involved in the phenylpropanoid pathway, which ultimately governs the fragrance of Rhododendron fortunei, we performed a comprehensive transcriptome and metabolomic analysis of the petals of two different varieties of two alpine rhododendrons: the scented R. fortunei and the unscented Rhododendron ‘Nova Zembla’. Results: Our transcriptomic and qRT–PCR data showed that nine candidate genes were highly expressed in R. fortunei but were downregulated in Rhododendron ‘Nova Zembla’. Among these genes, EGS expression was significantly positively correlated with various volatile benzene/phenylpropanoid compounds and significantly negatively correlated with the contents of various nonvolatile compounds, whereas CCoAOMT, PAL, C4H, and BALDH expression was significantly negatively correlated with the contents of various volatile benzene/phenylpropanoid compounds and significantly positively correlated with the contents of various nonvolatile compounds. CCR, CAD, 4CL, and SAMT expression was significantly negatively correlated with the contents of various benzene/phenylpropanoid compounds. The validation of RfSAMT showed that the RfSAMT gene regulates the synthesis of aromatic metabolites in R. fortunei. Conclusion: The findings of this study indicated that key candidate genes and metabolites involved in the phenylpropanoid biosynthesis pathway may govern the fragrance of R. fortunei. This lays a foundation for further research on the molecular mechanism underlying fragrance in the genus Rhododendron.

The firmness of grape berries is a critical factor influencing their commercial feasibility and is highly valued by both breeders and consumers. However, grape berry firmness is a complex quantitative trait governed by multiple genes, and our understanding of its genetic regulatory network remains incomplete. To elucidate the genetic mechanisms underlying grape berry firmness, this study employed genome-wide association studies (GWAS) to identify potential candidate genes associated with fruit firmness and cellulose content and to explore the gene regulatory network that controls their variation. The comprehensive GWAS results identified CesA as a candidate gene potentially regulating fruit firmness through its involvement in cellulose biosynthesis. To validate these findings, whole-genome gene family identification analysis was conducted. Furthermore, the key gene VvCslD5 was selected for functional validation, which included overexpression studies and subcellular localization. This study provides valuable insights into the regulation of biosynthesis and transcriptional signaling pathways that govern the structure of grape cell walls as well as the mechanisms underlying variations in grape firmness. These findings establish a solid foundation for future functional analyses of grape traits and will enhance breeding practices aimed at improving grape quality.

Rhododendron, a globally popular ornamental flower, is nevertheless limited in our understanding of the mechanisms underlying its fragrance formation. Notably, terpenoids are the most prevalent volatile metabolite produced by plants. In this study, gas chromatography–mass spectrometry (GC–MS), liquid chromatography–mass spectrometry (LC–MS) and transcriptomics sequencing were conducted to analyze the synthesis mechanisms of terpenoid fragrance compounds of petals in fragrant R. fortunei Lindl. (YJ) and non-fragrant R. “Nova Zembla” (NW). The results identified that (-)-myrtenol, linalool, pinene, myrtenyl acetate, and terpineol were key floral aroma substances in YJ. Furthermore, an analysis of KEGG enrichment and differentially expressed genes (DEGs) revealed that the bud and decay stages exhibited the highest number of enriched DEGs among different aroma types, indicating these as critical stages for the synthesis of terpenoid floral compounds. In this study, a structural gene, denoted as RfFDPS, was identified as a negative regulatory gene for monoterpene accumulation and a positive regulatory gene for sesquiterpene accumulation in YJ. Utilizing subcellular localization technology, we determined that RfFDPS proteins are located in the cytoplasm. A functional analysis through transient expression and gene silencing of RfFDPS demonstrated its ability to regulate the accumulation of monoterpenes and sesquiterpenes. The overexpression of RfFDPS led to an increase in the expression of structural genes related to terpenoid synthesis, resulting in a decrease in monoterpenes and an increase in sesquiterpenes. Conversely, gene silencing had the opposite effect. In conclusion, RfFDPS plays a pivotal role in the synthesis and release of terpenoid volatile compounds in YJ petals, laying a solid theoretical foundation for the cultivation and enhancement of aromatic R. species.

Aroma is one of the most important indicators of grape quality. Girdling and foliar fertilization with K (K₂O) are common agronomic practices applied to improve berry quality in grape production. However, little is known about its effect on the accumulation and biosynthesis of the entire aromatic profile. Our study was aimed to explore the influences of girdling and foliar fertilization with K (alone or in combination) on the general properties, phenolic composition, volatile free aroma compounds, spatial and temporal expression of terpene-related genes and sensory properties in ‘Hanxiangmi’ table grape. In this study, we found that girdling and foliar fertilization with K (alone or in combination) facilitated fruit enlargement and increased the accumulation of phenolic compounds in skin. The combination treatment of girdling and foliar fertilization with K significantly promoted the concentrations of total soluble solids (TSS) in the pulp and proanthocyanidins in the berry skin, and had a lower titratable acidity (TA) compared to those of the control. In contrast, girdling treatment alone increased the concentrations of titratable acidity. Volatile free aroma composition analysis revealed that the combination treatment increased the volatile compounds and concentrations significantly, most notably in terpenes, such as nerol, citronellol and linalool. Spatial and temporal expression analysis showed that the expression level of VvDXS was significantly correlated with linalool and total terpenes concentrations, as a result of which, we speculated that VvDXS is the candidate gene for the regulation of important grape terpenes. We hope that our results can direct farmers to better apply girdling and foliar fertilization with K in grape production.

Grapes are prone to softening, which limits their shelf life and suitability for long-distance transport. This study explored the molecular mechanisms underlying the effects of the chemical preservatives gibberellin (GA₃) and the nitric oxide donor sodium nitroprusside (SNP) on grape firmness. Enhancing grape quality, prolonging shelf life, and extending market supply were key objectives. Using transcriptomic and physicochemical analyses, the study found that treatments with 3 mmol/L GA₃ and 20 μmol/L SNP significantly increased the firmness of ‘Yinhong’ grapes, thereby improving overall quality. The mechanisms of action, however, differed between the two treatments. GA₃ inhibited pectin degradation and promoted cellulose accumulation, whereas SNP enhanced lignin and cellulose accumulation, by modulating cell wall metabolism. Furthermore, transcription factors such as CYPs, NAC043, and WRKY33 were identified as key regulators working in concert with target genes to influence berry firmness. These findings highlight the critical roles of GA₃ and SNP in improving grape quality and extending storage potential.

Background: Monoterpenes are among the most important volatile aromatic compounds contributing to the flavor and aroma of grapes and wine. However, the molecular basis of monoterpene biosynthesis has not yet been fully elucidated. Results: In our study, transcriptomics and gas chromatography-mass spectrometry (GC-MS) were used to mine candidate genes and transcription factors involved in monoterpene biosynthesis between high-monoterpene and zero-monoterpene table grape cultivars. We found that monoterpene biosynthesis was positively correlated by the expression of five genes encoding 1-deoxy-D-xylulose-5-phosphate synthase (VvDXSs), one encoding 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (VvHDR), three hydroxy-3-methylglutaryl-CoA synthases (VvHMGSs) and one mevalonate kinase (VvMVK), whereas the expression of one isopentenyl diphosphate isomerase (VvIDI) and one 3-hydroxy-3-methylglutaryl-CoA reductase (VvHMGR) negatively correlated monoterpene biosynthesis. Of these genes, VvIDI was selected to validate its function in monoterpene accumulation through a transient overexpression experiment, and was shown to inhibit the biosynthesis of grape linalool and α-terpineol. Meanwhile, we found that a 64-amino acid extension sequence at the N-terminus can guide the VvIDI protein to target the chloroplast. Conclusions: The findings of this study should help to guide future functional analysis of key genes as well as mining the potential regulatory mechanism of monoterpene biosynthesis in grapes and grape products.