Identification of the key genes contributing to the LOX-HPL volatile aldehyde biosynthesis pathway in jujube fruit

Discovery and Molecular Characterization of a Novel 9S-Lipoxygenase from Enhygromyxa salina for Fatty Acid Biotransformations

Iron-dependent lipoxygenases (LOXs) are involved in the synthesis of oxylipins from polyunsaturated fatty acids. However, they are usually difficult to overexpress in functional form in microbial cell factories. Moreover, 9-LOXs, generating 9-hydroperoxy fatty acids from C18 polyunsaturated fatty acids, have rarely been found from microbial sources. Here, we discovered a novel 9S-LOX in the marine myxobacterium Enhygromyxa salina (Es-9S-LOX). The recombinant enzyme produced in Escherichia coli exhibited remarkable activity in the dioxygenation of linoleic acid (LA, 1), α-linolenic acid, γ-linolenic acid, and arachidonic acid specifically at the C9 position to yield the product with (S)-configuration at catalytic efficiency of 3.94, 1.42, 1.38, and 0.69 μM-1·s-1, respectively. The elucidated X-ray crystal structure of Es-9S-LOX reveals a long and narrow hydrophobic pocket that allows the substrate to be near the metal ion and the oxygen tunnel. The enzyme was successfully used in a chemoenzymatic reaction to generate a hydroxy fatty acid from LA. Our study thus contributes to the valorization of renewable polyunsaturated fatty acids into a variety of fatty acid derivatives, including hydroxy fatty acids.

Integrated Metabolomics and Proteomics Analysis Provides Insights into the Formation of Volatile Compounds in Three Different Polyembryonic Mango Cultivars

Understanding volatile compound formation is critical for enhancing the flavor quality of mangoes. Integrated untargeted metabolomics and proteomics were employed to explore volatile compound formation in three different polyembryonic mango cultivars ("Ah Ping," "Rosa," and "Rosigold"). A total of 87 volatile compounds were identified using SPME-GC-MS. Untargeted metabolomics and proteomics resulted in identification of 508 metabolites and 4481 proteins, respectively. Integrative analysis revealed that the volatile compound formation was influenced by fatty acids, amino acids, pentose, and hexose, as well as terpenoid metabolisms. Specifically, upward expression of core enzymes in lipoxygenanse pathway was responsible for the higher levels of some C6 and C9 volatile compounds in "Ah Ping." The differential expression of key enzymes in fatty acid degradation facilitates the varied contents of straight-chain volatile compounds. The upregulation of glutamate decarboxylase and branched-chain amino acid aminotransferase upstream of butanoate metabolism led to the highest levels of butyl esters in "Ah Ping." Furthermore, the different levels of volatile furan and pyran compounds might be attributed to differential expression of critical enzymes in pentose and hexose metabolism. These findings established a metabolic and proteomic map unraveling the biosynthesis of specific volatile compounds and provided insights into understanding the characteristic flavor of mango.

Oxylipin biosynthesis via an unprecedented 16-hydroperoxide lyase pathway in green tissues of cucumber (Cucumis sativus L.) plants

The plant lipoxygenase cascade is a source of various regulatory oxylipins that play a role in cell signalling, stress adaptation, and immune response. Recently, we detected an unprecedented 16(S)-lipoxygenase, CsLOX3, in the leaves and fruit pericarp of cucumber (Cucumis sativus L.). In the present work, an array of products biosynthesized through the conversions of α-linolenic acid 16-hydroperoxide (16-HPOT) was detected. Firstly, a prominent 15-hydroxy-9,12-pentadecadienoic acid (Me/TMS) was detected, the product of hydroperoxide lyase (HPL) chain cleavage of 16-HPOT and further reduction of aldehyde 15-oxo-9,12-pentadecadienoic acid to alcohol. Besides, the presence of dicarboxylic acid, 3,6-pentadecadiene-1,15-dioic acid, was deduced from the detection of its catalytic hydrogenation product, pentadecane-1,15-dioic acid. Finally, 12,15-dihydroxypentadecanoic acid (Me/TMS) was detected amongst the hydrogenated products, thus indicating the presence of the parent 12,15-dihydroxy-9,13-pentadecadienoic acid. To confirm the proposed HPL chain cleavage, the 16(S)-HPOT was prepared and incubated with the recombinant cucumber HPL CYP74B6 enzyme. The CYP74B6 possessed high activity towards 16-HPOT. Chain cleavage yields the (9Z,12Z)-15-oxo-9,12-pentadecadienoic acid, undergoing a spontaneous isomerization into (9Z,13E)-15-oxo-9,13-pentadecadienoic acid. Thus, the cucumber plants as well as the recombinant cucumber HPL CYP74B6 possessed unprecedented 16-HPL activity, cleaving 16-HPOT into a C15 fragment, 15-oxo-9,12-pentadecadienoic acid, and a complementary volatile C3 fragment, propionic aldehyde. The 16-LOX/16-HPL route of oxylipin biosynthesis presents a novel facet of the plant LOX pathway.

Formation of lipid-derived volatile products through lipoxygenase (LOX)- and hydroperoxide lyase (HPL)- mediated pathway in oat, barley and soy bean

The aim of this study was to explore the formation of volatile lipid oxidation products by the lipoxygenase (LOX)-hydroperoxide lyase (HPL)-mediated pathway in oat, barley and soy bean. LOX activity was found only in barley and soy bean samples, but the lipase and HPL activity was detected in all samples. HPL showed particularly high activity with 13-hydroperoxides, while the activity was quite low when using 9-hydroperoxides, especially in the oat and barley. The optimum pH for HPL in different samples was similar, i.e., pH 6-7. In this condition, the volatile compounds formed dramatically with aldehydes and furans as the dominant products. Furthermore, a remarkable enzymatic degradation of lipids occurred during the preparation of food models with highly refined rapeseed oil (RO) and rapeseed oil fatty acid (ROFA) emulsions, where the ROFAs were more prone to oxidation than RO. This study shows the significance of lipid-degrading enzymes in plant-food flavour formation.

Decoding the Effects of High Hydrostatic Pressure and High-Temperature Short-Time Sterilization on the Volatile Aroma Profile of Red Raspberry Juice

The loss of distinctive aromas due to sterilization significantly hinders efforts to enhance the sensory quality of fruit and vegetable juices. This study aimed to elucidate the impacts of high-hydrostatic pressure (HHP) and high-temperature short-time (HTST) sterilization methods on the loss of C6 aldehyde aroma-active compounds in red raspberry juice. External standard quantification and quantitative descriptive analysis (QDA) revealed a notable decline in the levels of hexanal and (Z)-3-hexenal following the HHP and HTST treatments (p < 0.05), resulting in a marked attenuation of the grassy aroma characteristic of red raspberry juice. Furthermore, a comprehensive examination of the precursors, pivotal enzymes, intermediates, and downstream aromas within the fatty acid metabolism pathway in different raspberry juice samples indicated that the C6 aldehydes loss induced by HHP and HTST sterilizations was primarily ascribed to the competitive inhibition of β-oxidation and the hindered enzymatic oxidation of fatty acids. These insights suggest that modifying sterilization protocols and enhancing enzymatic stability may help preserve the aroma integrity of raspberry juice. Our findings offer practical guidance for optimizing juice processing techniques to maintain flavor.

Controlled atmosphere storage drive proteomic change in Chinese Daohuaxiang

Although the use of a controlled atmosphere is one of the most successful storage techniques, the mechanism thereof in rice storage remains unclear. We stored aromatic rice cultivar Daohuaxiang in a package filled with 98 % N2 and 35 % CO2 for 3 months. We investigated 2-acetyl-1-pyrroline loss, enzyme activities, and proteomics changes of rice during storage. The results showed that the content of 2-acetyl-1-pyrroline was reduced by 37.40 %, 25.65 %, and 43.89 % during storage using 98 % N2, 35 % CO2 controlled atmosphere storage, and conventional storage. Controlled atmosphere storage slowed down the increase of malondialdehyde content in Daohuaxiang. The results showed that 26S proteasome regulatory particle triple-A ATPase subunit 6, superoxide dismutase, glutathione transferase, and other key proteins were upregulated during 35 % CO2 regulation. This study provided a meaningful basis for exploring the regulation strategy of aromatic rice quality and strengthening the quality control of aromatic rice industry.

Epoxyalcohol Synthase Branch of Lipoxygenase Cascade

Oxylipins are one of the most important classes of bioregulators, biosynthesized through the oxidative metabolism of unsaturated fatty acids in various aerobic organisms. Oxylipins are bioregulators that maintain homeostasis at the cellular and organismal levels. The most important oxylipins are mammalian eicosanoids and plant octadecanoids. In plants, the main source of oxylipins is the lipoxygenase cascade, the key enzymes of which are nonclassical cytochromes P450 of the CYP74 family, namely allene oxide synthases (AOSs), hydroperoxide lyases (HPLs), and divinyl ether synthases (DESs). The most well-studied plant oxylipins are jasmonates (AOS products) and traumatin and green leaf volatiles (HPL products), whereas other oxylipins remain outside of the focus of researchers' attention. Among them, there is a large group of epoxy hydroxy fatty acids (epoxyalcohols), whose biosynthesis has remained unclear for a long time. In 2008, the first epoxyalcohol synthase of lancelet Branchiostoma floridae, BfEAS (CYP440A1), was discovered. The present review collects data on EASs discovered after BfEAS and enzymes exhibiting EAS activity along with other catalytic activities. This review also presents the results of a study on the evolutionary processes possibly occurring within the P450 superfamily as a whole.

Biological Characteristics and Functional Analysis of the Linoleic Acid Synthase Gene ZjFAD2 in Jujube

Jujube fruit is rich in linoleic acid and other bioactive components and has great potential to be used for the development of functional foods. However, the roles of FAD2 genes in linoleic acid biosynthesis in jujube fruit remain unclear. Here, we identified 15 major components in jujube and found that linoleic acid was the main unsaturated fatty acid; major differences in the content and distribution of linoleic acid in the pulp and seeds were observed, and levels of linoleic acid decreased during fruit maturation. Analysis of the fatty acid metabolome, genome, and gene expression patterns of cultivated and wild-type jujube revealed five ZjFAD2 family members highly related to linoleic acid biosynthesis. The heterologous expression of these five ZjFAD2 family members in tobacco revealed that all five of these genes increased the content of linoleic acid. Additionally, transient expression of these genes in jujube fruit and the virus-induced gene silencing (VIGS) test further confirmed the key roles of ZjFAD2-11 and ZjFAD2-1 in the biosynthesis of linoleic acid. The results of this research provide valuable insights into the molecular mechanism underlying linoleic acid synthesis in jujube and will aid the development of quality-oriented breeding strategies.

Analysis of the Glycoside Hydrolase Family 1 from Wild Jujube Reveals Genes Involved in the Degradation of Jujuboside A

Jujubosides are the major medicinal ingredients of Ziziphi Spinosae Semen (the seed of wild jujube). To date, a complete understanding of jujuboside's metabolic pathways has not been attained. This study has systematically identified 35 β-glucosidase genes belonging to the glycoside hydrolase family 1 (GH1) using bioinformatic methods based on the wild jujube genome. The conserved domains and motifs of the 35 putative β-glucosidases, along with the genome locations and exon-intron structures of 35 β-glucosidase genes were revealed. The potential functions of the putative proteins encoded by the 35 β-glucosidase genes are suggested based on their phylogenetic relationships with Arabidopsis homologs. Two wild jujube β-glucosidase genes were heterologously expressed in Escherichia coli, and the recombinant proteins were able to convert jujuboside A (JuA) into jujuboside B (JuB). Since it has been previously reported that JuA catabolites, including JuB and other rare jujubosides, may play crucial roles in the jujuboside's pharmacological activity, it is suggested that these two proteins can be used to enhance the utilization potential of jujubosides. This study provides new insight into the metabolism of jujubosides in wild jujube. Furthermore, the characterization of β-glucosidase genes is expected to facilitate investigations involving the cultivation and breeding of wild jujube.