LC-MS-Based Profiling Provides New Insights into Apocarotenoid Biosynthesis and Modifications in Citrus Fruits

β-Cyclocitral from Lavandula angustifolia Mill. Exerts Anti-Aging Effects on Yeasts and Mammalian Cells via Telomere Protection, Antioxidative Stress, and Autophagy Activation

We used a replicative lifespan (RLS) experiment of K6001 yeast to screen for anti-aging compounds within lavender extract (Lavandula angustifolia Mill.), leading to the discovery of β-cyclocitral (CYC) as a potential anti-aging compound. Concurrently, the chronological lifespan (CLS) of YOM36 yeast and mammalian cells confirmed the anti-aging effect of CYC. This molecule extended the yeast lifespan and inhibited etoposide (ETO)-induced cell senescence. To understand the mechanism of CYC, we analyzed its effects on telomeres, oxidative stress, and autophagy. CYC administration resulted in notable increases in the telomerase content, telomere length, and the expression of the telomeric shelterin protein components telomeric-repeat binding factor 2 (TRF2) and repressor activator protein 1 (RAP1). More interestingly, CYC reversed H2O2-induced telomere damage and exhibited strong antioxidant capacity. Moreover, CYC improved the survival rate of BY4741 yeast under oxidative stress induced by 6.2 mM H2O2, increasing the antioxidant enzyme activity while reducing the reactive oxygen species (ROS), reactive nitrogen species (RNS), and malondialdehyde (MDA) levels. Additionally, CYC enhanced autophagic flux and free green fluorescent protein (GFP) expression in the YOM38-GFP-ATG8 yeast strain. However, CYC did not extend the RLS of K6001 yeast mutants, such as Δsod1, Δsod2, Δcat, Δgpx, Δatg2, and Δatg32, which lack antioxidant enzymes or autophagy-related genes. These findings reveal that CYC acts as an anti-aging agent by modifying telomeres, oxidative stress, and autophagy. It is a promising compound with potential anti-aging effects and warrants further study.

Cell wall breaking of Haematococcus pluvialis biomass facilitated by Baijiu jiuqu fermentation with simultaneously production of beverages

The microalgae Haematococcus pluvialis is a commercial source of natural astaxanthin. However, mature cells develop rigid three-layer wall structures and a repulsive odor. This study applied a liquid static fermentation system to screen hydrolyzing microorganisms for cell wall hydrolysis. Baijiu jiuqu and Gutian hongqu were found to have promising potential for application. The fermentation using 2% baijiu jiuqu and 2% glucose for pre-activation achieved comparable recovery of carotenoids to homogenizer disruption methods and produced stable fragrance which may be attributed to ethyl octanoate, hexyl formate, and phenethyl butyrate, as revealed by gas chromatography-mass spectrometry analysis. The abundance of astaxanthin molecules was slightly affected by fermentation with fold change < 2, while molecules with higher fold change (>10) were mainly carbohydrates, lipids, and steroids proving the safety of the fermentation. This study provides a new scheme for the biorefining of Haematococcus. pluvialis, potentially contributing to the industrial production of natural astaxanthin.

Gardenia carotenoid cleavage dioxygenase 4a is an efficient tool for biotechnological production of crocins in green and non-green plant tissues

Crocins are beneficial antioxidants and potential chemotherapeutics that give raise, together with picrocrocin, to the colour and taste of saffron, the most expensive spice, respectively. Crocins are formed from crocetin dialdehyde that is produced in Crocus sativus from zeaxanthin by the carotenoid cleavage dioxygenase 2L (CsCCD2L), while GjCCD4a from Gardenia jasminoides, another major source of crocins, converted different carotenoids, including zeaxanthin, into crocetin dialdehyde in bacterio. To establish a biotechnological platform for sustainable production of crocins, we investigated the enzymatic activity of GjCCD4a, in comparison with CsCCD2L, in citrus callus engineered by Agrobacterium-mediated supertransformation of multi genes and in transiently transformed Nicotiana benthamiana leaves. We demonstrate that co-expression of GjCCD4a with phytoene synthase and β-carotene hydroxylase genes is an optimal combination for heterologous production of crocetin, crocins and picrocrocin in citrus callus. By profiling apocarotenoids and using in vitro assays, we show that GjCCD4a cleaved β-carotene, in planta, and produced crocetin dialdehyde via C₃₀ β-apocarotenoid intermediate. GjCCD4a also cleaved C₂₇ β-apocarotenoids, providing a new route for C₁₇ -dialdehyde biosynthesis. Callus lines overexpressing GjCCD4a contained higher number of plastoglobuli in chromoplast-like plastids and increased contents in phytoene, C17:0 fatty acid (FA), and C18:1 cis-9 and C22:0 FA esters. GjCCD4a showed a wider substrate specificity and higher efficiency in Nicotiana leaves, leading to the accumulation of up to 1.6 mg/g dry weight crocins. In summary, we established a system for investigating CCD enzymatic activity in planta and an efficient biotechnological platform for crocins production in green and non-green crop tissues/organs.

One-pot synthesis of dihydro-β-ionone from carotenoids using carotenoid cleavage dioxygenase and enoate reductase

Dihydro-β-ionone is a characteristic aroma compound of Osmanthus fragrans and is widely applied in the flavor & fragrance industry. However, the main focus is on chemical synthesis due to the metabolic pathways of dihydro-β-ionone is still unclear. Here, we explored the one-pot synthesis system for dihydro-β-ionone production using carotenoid cleavage dioxygenase (CCD) and enoate reductase. After screening the CCD enzyme, PhCCD1 from the Petunia hybrid was identified as the suitable enzyme for the first step of dihydro-β-ionone synthesis due to the high enzyme activity for carotenoid. The PhCCD1 was expressed in Escherichia coli and further characterized. The optimal activity of PhCCD1 was observed at pH 6.8 and 45 °C. The enzyme was stable over the pH range of 6.0-8.0 and had good thermal stability below 40 °C. Then, we optimized the coupled reaction conditions for dihydro-β-ionone production by PhCCD1 and enoate reductase AaDBR1 from Artemisia annua. Furthermore, we introduced the NADPH regeneration system with a 1.5-fold enhancement for dihydro-β-ionone production. Collectively, approximately 13.34 mg/L dihydro-β-ionone was obtained by the one-pot biosystem with a corresponding molar conversion of 85.8%. For the first time, we successfully designed and constructed a new synthesis pathway for dihydro-β-ionone production in vitro. The coupled catalysis reported herein illustrates the feasibility of producing dihydro-β-ionone from carotenoids and guides further engineering in the food industry.

Bioactive Compounds of Citrus Fruits: A Review of Composition and Health Benefits of Carotenoids, Flavonoids, Limonoids, and Terpenes

The increased consumption of fruits, vegetables, and whole grains contributes to the reduced risk of many diseases related to metabolic syndrome, including neurodegenerative diseases, cardiovascular disease (CVD), diabetes, and cancer. Citrus, the genus Citrus L., is one of the most important fruit crops, rich in carotenoids, flavonoids, terpenes, limonoids, and many other bioactive compounds of nutritional and nutraceutical value. Moreover, polymethoxylated flavones (PMFs), a unique class of bioactive flavonoids, abundantly occur in citrus fruits. In addition, citrus essential oil, rich in limonoids and terpenes, is an economically important product due to its potent antioxidant, antimicrobial, and flavoring properties. Mechanistic, observational, and intervention studies have demonstrated the health benefits of citrus bioactives in minimizing the risk of metabolic syndrome. This review provides a comprehensive view of the composition of carotenoids, flavonoids, terpenes, and limonoids of citrus fruits and their associated health benefits.

Exploring the Diversity and Regulation of Apocarotenoid Metabolic Pathways in Plants

In plants, carotenoids are subjected to enzyme-catalyzed oxidative cleavage reactions as well as to non-enzymatic degradation processes, which produce various carbonyl products called apocarotenoids. These conversions control carotenoid content in different tissues and give rise to apocarotenoid hormones and signaling molecules, which play important roles in plant growth and development, response to environmental stimuli, and in interactions with surrounding organisms. In addition, carotenoid cleavage gives rise to apocarotenoid pigments and volatiles that contribute to the color and flavor of many flowers and several fruits. Some apocarotenoid pigments, such as crocins and bixin, are widely utilized as colorants and additives in food and cosmetic industry and also have health-promoting properties. Considering the importance of this class of metabolites, investigation of apocarotenoid diversity and regulation has increasingly attracted the attention of plant biologists. Here, we provide an update on the plant apocarotenoid biosynthetic pathway, especially highlighting the diversity of the enzyme carotenoid cleavage dioxygenase 4 (CCD4) from different plant species with respect to substrate specificity and regioselectivity, which contribute to the formation of diverse apocarotenoid volatiles and pigments. In addition, we summarize the regulation of apocarotenoid metabolic pathway at transcriptional, post-translational, and epigenetic levels. Finally, we describe inter- and intraspecies variation in apocarotenoid production observed in many important horticulture crops and depict recent progress in elucidating the genetic basis of the natural variation in the composition and amount of apocarotenoids. We propose that the illustration of biochemical, genetic, and evolutionary background of apocarotenoid diversity would not only accelerate the discovery of unknown biosynthetic and regulatory genes of bioactive apocarotenoids but also enable the identification of genetic variation of causal genes for marker-assisted improvement of aroma and color of fruits and vegetables and CRISPR-based next-generation metabolic engineering of high-value apocarotenoids.

Unraveling the versatility of CCD4: Metabolic engineering, transcriptomic and computational approaches

Carotenoids are economically valuable isoprenoids synthesized by plants and microorganisms, which play a paramount role in their overall growth and development. Carotenoid cleavage dioxygenases are a vast group of enzymes that specifically cleave thecarotenoids to produce apocarotenoids. Recently, CCDs are a subject of talk because of their contributions to different aspects of plant growth and due to their significance in the production of economically valuable apocarotenoids. Among them, CCD4 stands unique because of its versatility in performing metabolic roles. This review focuses on the multiple functionalities of CCD4 like pigmentation, volatile apocarotenoid production, stress responses, etc. Interestingly, through our literature survey we arrived at a conclusion that CCD4 could perform functions of other carotenoid cleaving enzymes.The metabolic engineering, transcriptomic, and computational approaches adopted to reveal the contributions of CCD4 were also considered here for the study.Phylogenetic analysis was performed to delve into the evolutionary relationships of CCD4 in different plant groups. A tree of 81CCD genes from 64 plant species was constructed, signifying the presence of well-conserved families. Gene structures were illustrated and the difference in the number and position of exons could be considered as a factor behind functional versatility and substrate tolerance of CCD4 in different plants.