Genetic Analysis of Methyl Anthranilate, Mesifurane, Linalool, and Other Flavor Compounds in Cultivated Strawberry (Fragaria × ananassa)

The cultivated strawberry (Fragaria × ananassa) is an economically important fruit crop that is intensively bred for improved sensory qualities. The diversity of fruit flavors and aromas in strawberry results mainly from the interactions of sugars, acids, and volatile organic compounds (VOCs) that are derived from diverse biochemical pathways influenced by the expression of many genes. This study integrates multiomic analyses to identify QTL and candidate genes for multiple aroma compounds in a complex strawberry breeding population. Novel fruit volatile QTL was discovered for methyl anthranilate, methyl 2-hexenoate, methyl 2-methylbutyrate, mesifurane, and a shared QTL on Chr 3 was found for nine monoterpene and sesquiterpene compounds, including linalool, 3-carene, β-phellandrene, α-limonene, linalool oxide, nerolidol, α-caryophellene, α-farnesene, and β-farnesene. Fruit transcriptomes from a subset of 64 individuals were used to support candidate gene identification. For methyl esters including the grape-like methyl anthranilate, a novel ANTHANILIC ACID METHYL TRANSFERASE–like gene was identified. Two mesifurane QTL correspond with the known biosynthesis gene O-METHYL TRANSFERASE 1 and a novel FURANEOL GLUCOSYLTRANSFERASE. The shared terpene QTL contains multiple fruit-expressed terpenoid pathway-related genes including NEROLIDOL SYNTHASE 1 (FanNES1). The abundance of linalool and other monoterpenes is partially governed by a co-segregating expression-QTL (eQTL) for FanNES1 transcript variation, and there is additional evidence for quantitative effects from other terpenoid-pathway genes in this narrow genomic region. These QTLs present new opportunities in breeding for improved flavor in commercial strawberry.

Developing a Yeast Platform Strain for an Enhanced Taxadiene Biosynthesis by CRISPR/Cas9

Paclitaxel is an important diterpenoid commonly used as an anticancer drug. Although the paclitaxel biosynthetic pathway has been mostly revealed, some steps remain to be elucidated. The difficulties in plant transformations and the scarcity of the precursor of paclitaxel, (+)-taxa-4(5), 11(12)-diene (taxadiene), have hindered the full comprehension of paclitaxel biochemistry and, therefore, its production by biotechnological approaches. One solution is to use the budding yeast, Saccharomyces cerevisiae, as a platform to elucidate the paclitaxel biosynthesis. As taxadiene is a diterpenoid, its common precursor, geranylgeranyl pyrophosphate (GGPP), needs to be increased in yeast. In this study, we screened various GGPP synthases (GGPPS) to find the most suitable GGPPS for taxadiene production in yeast. We also optimized the taxadiene production by increasing the flux toward the terpenoid pathway. Finally, to remove selection markers, we integrated the required genes using a CRISPR/Cas9 system in the yeast genome. Our result showed that a titer of 2.02 ± 0.40 mg/L (plasmid) and 0.41 ± 0.06 mg/L (integrated) can be achieved using these strategies. This platform strain can be used to readily test the gene candidates for microbial paclitaxel biosynthesis in the future.

Is aromatic terpenoid composition of grapes in Northwestern Iberian wine cultivars related to variation in VviDXS1 gene?

BACKGROUND: Monoterpenes and C13-norisoprenoids are key terpenoid compounds for wine aroma. The enzyme encoded by VviDXS1 participates in terpenoid biosynthesis in grapevine fruits and gain-of-function mutations in this gene lead to characteristic muscat aroma. OBJECTIVE: To assess for VviDXS1 contribution to aroma variation in Northwestern Iberian wine cultivars, we resequenced this gene in 111 cultivars and compared grape juice terpenic composition in 12 of them. METHODS: VviDXS1 was capture-targeted for resequencing with Illumina paired-end reads, SAMtools was used for variant calling and gene haplotypes were reconstructed with PHASE. Monoterpenes and C13-norisoprenoids were quantified in free and glycosidically-bound forms from grape juice by gas chromatography-mass spectrometry. RESULTS: Terpenic composition discriminated between muscat, terpenic and neutral profiles across cultivars. While the terpenic profile of Loureira and Albariño white cultivars was not associated with muscat-like mutations, Albariño carries a V34L substitution in VviDXS1 that is also present in other aromatic cultivars and was not reported before. Tempranillo and Cabernet Sauvignon red cultivars accumulated higher levels of C13-norisoprenoids, which was not associated with specific variation in VviDXS1. CONCLUSIONS: Apart from the uncharacterized substitution present in Albariño, findings suggest that terpenoid pathway-related genes other than VviDXS1 could contribute to the aromatic attributes of these cultivars.

The Evolutionary Rate Variation Among Genes of MVA and MEP Pathways in Plant Terpenoid Biosynthesis

Background: Terpenoids are one of the most important compounds in plants, play an significant biological defense and developmental roles in numerous plant species, and widely used for industrial chemicals. Many previous studies have completed the identification of terpenoid biosynthetic pathway and related genes. However, few studies have focused on the molecular evolution analysis of terpenoid pathway genes in plants. In this study, we researched the evolutionary rate variation pattern of 16 terpenoid pathway genes in 12 species with a broad taxonomic span. Results: We retrieved 14 genes in MVA and MEP pathways and 2 extra genes from 12 species, respectively. The evolutionary parameters dN values and dN/ dS ratios are varied significantly among genes, and the dN/ dS ratios of most genes are varied substantially among lineages. The MVA and MEP pathways genes have different evolutionary rate variation pattern, although no significant difference in dN/ dS ratios between two pathways genes. For MVA pathway, the downstream genes exhibits the greater dN/ dS ratio than upstream genes. For MEP pathway, the three midstream genes evolves more rapidly than other genes, and most of MEP pathway genes were detected the signature of positive selection under random sites models. Moreover, the dN/ dS ratios of MVA and MEP pathways genes are negatively correlated with pathway position and PPI, and coding sequence length, respectively. Conclusions: Taken together, the results indicated that the evolutionary rate variation of MVA pathway genes is mainly attributed to differential selective constraint rather than the positive selection. However, the differential selective constraint relaxation and positive selection collectively shaped the evolutionary rate heterogeneity of MEP pathway genes.

Genetic Analysis of Methyl Anthranilate, Mesifurane, Linalool and Other Flavor Compounds in Cultivated Strawberry (Fragaria ×ananassa)

ABSTRACTThe cultivated strawberry (Fragaria ×ananassa) is an economically important fruit crop that is intensively bred for improved sensory qualities. The diversity of fruit flavors and aromas in strawberry result mainly from the interactions of sugars, acids, and volatile organic compounds (VOCs) that are derived from diverse biochemical pathways influenced by the expression of many genes. This study integrates multi-omics analyses to identify QTL and candidate genes for multiple aroma compounds in a complex strawberry breeding population. Novel fruit volatile QTL were discovered for methyl anthranilate, methyl 2-hexenoate, methyl 2-methylbutyrate, mesifurane, and a shared QTL on Chr 3 was found for nine monoterpene and sesquiterpene compounds, including linalool, 3-carene, β-phellandrene, α-limonene, linalool oxide, nerolidol, α-caryophellene, α-farnesene, and β-farnesene. Fruit transcriptomes from a subset of sixty-four individuals were used to support candidate gene identification. For methyl esters including the grape-like methyl anthranilate, a novel ANTHANILIC ACID METHYL TRANSFERASE–like gene was identified. Two mesifurane QTL correspond with the known biosynthesis gene O-METHYL TRANSFERASE 1 and a novel FURANEOL GLUCOSYLTRANSFERASE. The shared terpene QTL contains multiple fruit-expressed terpenoid pathway-related genes including NEROLIDOL SYNTHASE 1 (FanNES1). The abundance of linalool and other monoterpenes is partially governed by a co-segregating expression-QTL (eQTL) for FanNES1 transcript variation, and there is additional evidence for quantitative effects from other terpenoid-pathway genes in this narrow genomic region. These QTL present new opportunities in breeding for improved flavor in commercial strawberry.

Chemical Diversity and Biological Activities of Meroterpenoids from Marine Derived-Fungi: A Comprehensive Update

Meroterpenoids are a class of hybrid natural products, partially derived from a mixed terpenoid pathway. They possess remarkable structural features and relevant biological and pharmacological activities. Marine-derived fungi are a rich source of meroterpenoids featuring structural diversity varying from simple to complex molecular architectures. A combination of a structural variability and their myriad of bioactivities makes meroterpenoids an interesting class of naturally occurring compounds for chemical and pharmacological investigation. In this review, a comprehensive literature survey covering the period of 2009–2019, with 86 references, is presented focusing on chemistry and biological activities of various classes of meroterpenoids isolated from fungi obtained from different marine hosts and environments.

The Terpenoid Pathway: Products from Mevalonic Acid and Deoxyxylulose Phosphate

It was Otto Wallach (1847– 1931) who first coined the term “terpene” and made the observation that many plant-derived essential oils had chemical structures whose composition was based on multiples of a basic five-carbon unit. His work with turpentine and the organic products derived from it was consistent with earlier studies of natural rubber which had shown that its thermal decomposition released “isoprene” (2-methyl-1,3-butadiene) as the principal product. This led eventually to the formulation of the so-called biogenetic isoprene rule of Leopold Ruzicka (1887–1976) in 1953 which stated that “the carbon skeleton of the terpenes is composed of isoprene units linked in regular or irregular arrangement.” As it turns out, biosynthetic pathways to terpenes are found in nearly all organisms, producing a remarkable variety of different structural types, as we will soon see. In fact, something in excess of over 25,000 different terpenes with a wide variety of biological functions have been isolated from the plant kingdom over the years. Interestingly, while many terpenes are simple achiral compounds, others are chiral as can be seen in the case of α-pinene in Fig. 4.1. But unlike the naturally occurring L-amino acids and D-carbohydrates, different organisms may produce the same terpene product but in different enantiomeric forms. For example, limonene is formed by more than 300 plants, with the (+)-(R) enantiomer being the most widespread form as the major constituent of citrus peel essential oils (orange oil). As the most abundant of all terpenes, its pleasant citrus fragrance and flavor have led to its worldwide use in the food and fragrance industries and also as a botanical insecticide. A number of plants produce both enantiomers of limonene, while others produce only the (−)-(S)-enantiomer which possesses a strong pine smell reminiscent of turpentine. This obviously speaks to the chirality and enantioselectivity of our own olfactory receptor sites which can readily distinguish between the two enantiomers, thus signaling a different odor response in each case.