Transcriptomic and Metabolic Analyses Provide New Insights into the Effects of Exogenous Sucrose on Monoterpene Synthesis in "Muscat Hamburg" Grapes

Evolution of green leaf volatile profile and aroma potential during the berry development in five Vitis vinifera L. Cultivars

Green leaf volatiles (GLVs), play important roles in the green and fresh aroma characteristics of grape berries. The evolution of GLV profiles regarding the varietal difference during grapevine phenological ripening is not well understood. This study generated the GLV profiles of five Vitis vinifera L. cultivars ('Cabernet Sauvignon,' 'Cabernet Franc,' 'Cabernet Gernischt,' 'Chardonnay,' and 'Sauvignon Blanc') at five ripening stages. GLVs were distinctive at different E-L stages for each grape variety. (E)-2-hexen-1-ol, 1-hexanol, and hexanal were the dominant components in all mature berries. In terms of total GLV content, all varieties reached the maximum at maturity in the 2019 vintage, and the total GLV content was higher in mature Sauvignon Blanc and Cabernet Sauvignon grapes. In the 2020 vintage, the total GLV content in Chardonnay and Sauvignon Blanc berries rapidly accumulated at veraison and peaked before harvest. The present results could help winemakers create a good balance of wine aroma.

Analysis of Important Volatile Organic Compounds and Genes Produced by Aroma of Pepper Fruit by HS-SPME-GC/MS and RNA Sequencing

Pepper is an important condiment, and its aroma affects its commercial value. In this study, transcriptome sequencing and combined headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) were used to analyze the differentially expressed genes and volatile organic compounds in spicy and non-spicy pepper fruits. Compared with non-spicy fruits, there were 27 up-regulated volatile organic compounds (VOCs) and 3353 up-regulated genes (Up-DEGs) in spicy fruits. The results of KEGG enrichment analysis of the Up-DEGs combined with differential VOCs analysis showed that fatty acid biosynthesis and terpenoid biosynthesis may be the main metabolic pathways for aroma differences between non-spicy and spicy pepper fruits. The expression levels of the fatty acid biosynthesis-related genes FAD, LOX1, LOX5, HPL, and ADH and the key terpene synthesis gene TPS in spicy pepper fruits were significantly higher than those in non-spicy pepper fruits. The differential expression of these genes may be the reason for the different aroma. The results can provide reference for the development and utilization of high-aroma pepper germplasm resources and the breeding of new varieties.

Plant secondary metabolic responses to global climate change: A meta-analysis in medicinal and aromatic plants

Plant secondary metabolites (SMs) play crucial roles in plant-environment interactions and contribute greatly to human health. Global climate changes are expected to dramatically affect plant secondary metabolism, yet a systematic understanding of such influences is still lacking. Here, we employed medicinal and aromatic plants (MAAPs) as model plant taxa and performed a meta-analysis from 360 publications using 1828 paired observations to assess the responses of different SMs levels and the accompanying plant traits to elevated carbon dioxide (eCO₂ ), elevated temperature (eT), elevated nitrogen deposition (eN) and decreased precipitation (dP). The overall results showed that phenolic and terpenoid levels generally respond positively to eCO₂ but negatively to eN, while the total alkaloid concentration was increased remarkably by eN. By contrast, dP promotes the levels of all SMs, while eT exclusively exerts a positive influence on the levels of phenolic compounds. Further analysis highlighted the dependence of SM responses on different moderators such as plant functional types, climate change levels or exposure durations, mean annual temperature and mean annual precipitation. Moreover, plant phenolic and terpenoid responses to climate changes could be attributed to the variations of C/N ratio and total soluble sugar levels, while the trade-off supposition contributed to SM responses to climate changes other than eCO₂ . Taken together, our results predicted the distinctive SM responses to diverse climate changes in MAAPs and allowed us to define potential moderators responsible for these variations. Further, linking SM responses to C-N metabolism and growth-defence balance provided biological understandings in terms of plant secondary metabolic regulation.

Transcriptomics Integrated with Metabolomics Reveals the Effect of Cluster Thinning on Monoterpene Biosynthesis in 'Muscat Hamburg' Grape

Monoterpenes are crucial to floral and fruit aromas in grapes and wines. Cluster thinning is a common practice for improving grape quality. Using Vitis vinifera cv. Muscat Hamburg, the effects of three cluster-thinning regimes on the biosynthesis and accumulation of monoterpenes from véraison to harvest were investigated at the transcriptomics and targeted metabolomics levels. It was observed that more intense thinning produced higher concentrations of total monoterpenes, particularly in their bound forms. The numbers of differentially expressed genes among the three treatments were 193, 200, and 238 at the three developmental stages. In total, 10 modules were identified from a weighted gene correlation network analysis, and one module including 492 unigenes was associated with monoterpene metabolism. These findings provide new insights into the molecular basis of the relationship between cluster thinning and monoterpene biosynthesis in Muscat Hamburg grape. Cluster thinning could be carefully considered for its application in production.