Differential expression pattern of an acidic 9/13-lipoxygenase in flower opening and senescence and in leaf response to phloem feeders in the tea plant

OsLOX1 positively regulates seed vigor and drought tolerance in rice

The lipoxygenase (LOX) gene family is widely distributed in plants, and its activity is closely associated with seed viability and stress tolerance. In this study, we cloned the rice(Oryza sativa)lipoxygenase gene OsLOX1, a key participant in the 13-lipoxygenase metabolic pathway. Our primary focus was to investigate its role in mediating responses to drought stress and seed germination in rice. Histochemical staining and qPCR analysis indicated that the expression level of OsLOX1 was relatively high in leaves and early germinating seeds. Our findings revealed that mutant lines with CRISPR/Cas9-induced knockout of OsLOX1 exhibited reduced tolerance to drought stress compared with the wild-type. This was accompanied by elevated levels of H2O2 and malondialdehyde, and a decrease in the expression levels of genes associated with antioxidant enzymes. Furthermore, knockout of OsLOX1 reduced the longevity of rice seeds increased H2O2 and MDA levels, and decreased the activities of the antioxidant enzymes superoxide dismutase and catalase, compared with the wild-type. These findings demonstrated that OsLOX1 positively regulated rice seed vigor and drought stress.

Localization and activity of lipoxygenase in the ovule of Larix kaempferi (Lamb.) Carr. during female gametophyte maturation

KEY MESSAGE

Lipoxygenase activity and localization vary throughout the development of Larix kaempferi ovules, with the highest enzyme activity observed in ovules at the cellular stage and the most intense immunogold reaction noted at the mature archegonium stage of gametophyte development. Lipoxygenases are a family of oxidoreductases with a significant role in biological systems, widespread in living organisms e.g. mammals, fish, corals, plants, mosses, algae, fungi, yeasts, and bacteria. Lipoxygenase activity in plants leads to the formation of phytooxylipins, i.e. signaling molecules, which play a crucial role in many significant physiological processes such as male and female gametophyte maturation, germination and seedling growth, pathogen resistance, abiotic stress response, fruit ripening, and senescence. The activity and localization of lipoxygenase change during plant growth and development. The localization of lipoxygenase in a developing ovule of Larix kaempferi was analyzed using the immunogold labeling method, and the activity was determined spectrophotometrically with linolenic acid as a substrate. Among the investigated stages, the immunogold reaction was the most intense at the mature archegonium stage in the ovule. Lipoxygenase was found in all parts of the L. kaempferi ovule. The largest number of immunogold particles was detected in the integument cells of all the analyzed stages of ovule development. Only one isoform of lipoxygenase with an optimum at pH 8 was active in the ovules during female gametophyte maturation. The highest enzyme activity was determined at the cellular stage, whereas the mature archegonium stage was characterized by its lowest level, which means that LOX activity in developing ovules of the Japanese larch is not correlated with the number of antibody-labeled molecules of the enzyme.

Dynamic Change of Volatile Fatty Acid Derivatives (VFADs) and Their Related Genes Analysis during Innovative Black Tea Processing

Volatile fatty acid derivatives (VFADs) play a significant role in contributing to flowery-fruity flavor black tea. Innovative black tea is typically crafted from aroma-intensive tea cultivars, such as Jinmudan, using defined production methodologies. In this study, the during-processing tea leaves of innovative black tea were applied as materials, and we selected a total of 45 VFADs, comprising 11 derived aldehydes, nine derived alcohols, and 25 derived esters. Furthermore, the dynamic variations of these VFADs were uncovered. Transcriptome analysis was performed to identify genes involved in the LOX (lipoxygenase) pathway, resulting in the identification of 17 CsLOX genes, one hydrogen peroxide lyase (CsHPL) gene, 11 alcohol dehydrogenases (CsADH) genes, 11 genes as acyl CoA oxidase (CsACOX) genes, and three allene oxide synthase (CsAOS) genes. Additionally, the expression levels of these genes were measured, indicating that the processing treatments of innovative black tea, particularly turn-over and fermentation, had a stimulation effect on most genes. Finally, qRT-PCR verification and correlation analysis were conducted to explain the relationship between VFADs and candidate genes. This study aims to provide a reference for illuminating the formation mechanisms of aroma compounds in innovative black tea, thereby inspiring the optimization of innovative processing techniques and enhancing the overall quality of black tea.

Multifactorial optimization enables the identification of a greener method to produce (+)-nootkatone

The natural aroma compound (+)-nootkatone was obtained in selective conversions of up to 74 mol% from inexpensive (+)-valencene substrate by using a comparatively greener biocatalytic process developed based on modifications of the previously published Firmenich method. Buffer identity and concentration, pH, temperature and downstream work-up procedures were optimized to produce a crude product in which >90 % of (+)-valencene had been converted, with high chemoselectivity observed for (+)-nootkatone production. Interestingly, the biotransformation was carried out efficiently at temperatures as low as 21 ºC. Surprisingly, the best results were obtained when an acidic pH in the range of 3-6 was applied, as compared to the previously published procedure in which it appeared to be necessary to buffer the pH optimally and fixed throughout at 8.5. Furthermore, there was no need to maintain a pure oxygen atmosphere to achieve good (+)-nootkatone yields. Instead, air bubbled continuously at a low rate through the reaction mixture via a submerged glass capillary was sufficient to enable the desired lipoxygenase-catalyzed oxidation reactions to occur efficiently. No valencene epoxide side-products were detected in the organic product extract by a standard GCMS protocol. Only traces of the anticipated corresponding α- and β-nootkatol intermediates were routinely observed.

Physiological and Transcriptomic Analyses Reveal the Mechanisms Underlying Methyl Jasmonate-Induced Mannitol Stress Resistance in Banana

Exogenous methyl jasmonate (MeJA) application has shown promising effects on plant defense under diverse abiotic stresses. However, the mechanisms underlying MeJA-induced stress resistance in bananas are unclear. Therefore, in this study, we treated banana plants with 100 μM MeJA before inducing osmotic stress using mannitol. Plant phenotype and antioxidant enzyme activity results demonstrated that MeJA improved osmotic stress resistance in banana plants. Thereafter, to explore the molecular mechanisms underlying MeJA-induced osmotic stress resistance in banana seedlings, we conducted high-throughput RNA sequencing (RNA-seq) using leaf and root samples of "Brazilian" banana seedlings treated with MeJA for 0 h and 8 h. RNA-seq analysis showed that MeJA treatment upregulated 1506 (leaf) and 3341 (root) genes and downregulated 1768 (leaf) and 4625 (root) genes. Then, we performed gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses on the differentially expressed genes. We noted that linoleic acid metabolism was enriched in both root and leaf samples, and the genes of this pathway exhibited different expression patterns; 9S-LOX genes were highly induced by MeJA in the leaves, whereas 13S-LOX genes were highly induced in the roots. We also identified the promoters of these genes, as the differences in response elements may contribute to tissue-specific gene expression in response to MeJA application in banana seedlings. Overall, the findings of this study provide insights into the mechanisms underlying abiotic stress resistance in banana that may aid in the improvement of banana varieties relying on molecular breeding.

A genome-wide study of the lipoxygenase gene families in Medicago truncatula and Medicago sativa reveals that MtLOX24 participates in the methyl jasmonate response

BACKGROUND

Lipoxygenase (LOX) is a multifunctional enzyme that is primarily related to plant organ growth and development, biotic and abiotic stress responses, and production of flavor-associated metabolites. In higher plants, the LOX family encompasses several isozymes with varying expression patterns between tissues and developmental stages. These affect processes including seed germination, seed storage, seedling growth, fruit ripening, and leaf senescence. LOX family genes have multiple functions in response to hormones such as methyl jasmonate (MeJA) and salicylic acid.

RESULTS

In this study, we identified 30 and 95 LOX homologs in Medicago truncatula and Medicago sativa, respectively. These genes were characterized with analyses of their basic physical and chemical properties, structures, chromosomal distributions, and phylogenetic relationships to understand structural variations and their physical locations. Phylogenetic analysis was conducted for members of the three LOX subfamilies (9-LOX, type I 13-LOX, and type II 13-LOX) in Arabidopsis thaliana, Glycine max, M. truncatula, and M. sativa. Analysis of predicted promoter elements revealed several relevant cis-acting elements in MtLOX and MsLOX genes, including abscisic acid (ABA) response elements (ABREs), MeJA response elements (CGTCA-motifs), and antioxidant response elements (AREs). Cis-element data combined with transcriptomic data demonstrated that LOX gene family members in these species were most likely related to abiotic stress responses, hormone responses, and plant development. Gene expression patterns were confirmed via quantitative reverse transcription PCR. Several MtLOX genes (namely MtLOX15, MtLOX16, MtLOX20, and MtLOX24) belonging to the type I 13-LOX subfamily and other LOX genes (MtLOX7, MtLOX11, MsLOX23, MsLOX87, MsLOX90, and MsLOX94) showed significantly different expression levels in the flower tissue, suggesting roles in reproductive growth. Type I 13-LOXs (MtLOX16, MtLOX20, MtLOX21, MtLOX24, MsLOX57, MsLOX84, MsLOX85, and MsLOX94) and type II 13-LOXs (MtLOX5, MtLOX6, MtLOX9, MtLOX10, MsLOX18, MsLOX23, and MsLOX30) were MeJA-inducible and were predicted to function in the jasmonic acid signaling pathway. Furthermore, exogenous MtLOX24 expression in Arabidopsis verified that MtLOX24 was involved in MeJA responses, which may be related to insect-induced abiotic stress.

CONCLUSIONS

We identified six and four LOX genes specifically expressed in the flowers of M. truncatula and M. sativa, respectively. Eight and seven LOX genes were induced by MeJA in M. truncatula and M. sativa, and the LOX genes identified were mainly distributed in the type I and type II 13-LOX subfamilies. MtLOX24 was up-regulated at 8 h after MeJA induction, and exogenous expression in Arabidopsis demonstrated that MtLOX24 promoted resistance to MeJA-induced stress. This study provides valuable new information regarding the evolutionary history and functions of LOX genes in the genus Medicago.

Tetraclinis articulata essential oil emulsion use as alternative to chemical fungicide to control tomato grey mould disease

Tetraclinis articulata essential oil proved to be effective in controlling tomato grey mould, so we would investigate its effect on some tomato defense mechanisms. The pretreatment of Botrytis cinerea infected tomato plants with TAEO emulsion enhanced the activity of antioxidant enzymes activity SOD, CAT, APX, and GPX, and total polyphenols content and it decreased IC50 of free radical-scavenging activity and H2O2 content. Results showed amelioration in antioxidant status in TAEO emulsion treated and B. cinerea infected plants indicating that treatment decreased infection in tomato plants. The qRT-PCR analysis of defense genes expression Chitinase SlChi, transcription factors SlWRKY and SlAP2/ERF, Lipoxygenase SlLOX, and Thioredoxin SlTRX showed that they were up-regulated as early as 12 hpi sustained with a second increase at 48 hpi in TAEO emulsion pretreated and infected plants. These results suggest the potential use of TAEO emulsion as natural product to induce tomato antioxidant status and activate defense genes.

Volatile compound-mediated plant-plant interactions under stress with the tea plant as a model

Plants respond to environmental stimuli via the release of volatile organic compounds (VOCs), and neighboring plants constantly monitor and respond to these VOCs with great sensitivity and discrimination. This sensing can trigger increased plant fitness and reduce future plant damage through the priming of their own defenses. The defense mechanism in neighboring plants can either be induced by activation of the regulatory or transcriptional machinery, or it can be delayed by the absorption and storage of VOCs for the generation of an appropriate response later. Despite much research, many key questions remain on the role of VOCs in interplant communication and plant fitness. Here we review recent research on the VOCs induced by biotic (i.e. insects and pathogens) and abiotic (i.e. cold, drought, and salt) stresses, and elucidate the biosynthesis of stress-induced VOCs in tea plants. Our focus is on the role of stress-induced VOCs in complex ecological environments. Particularly, the roles of VOCs under abiotic stress are highlighted. Finally, we discuss pertinent questions and future research directions for advancing our understanding of plant interactions via VOCs.

Discovery of α-Linolenic Acid 16(S)-Lipoxygenase: Cucumber (Cucumis sativus L.) Vegetative Lipoxygenase 3

The GC-MS profiling of the endogenous oxylipins (Me/TMS) from cucumber (Cucumis sativus L.) leaves, flowers, and fruit peels revealed a remarkable abundance of 16-hydroxy-9,12,14-octadecatrienoic acid (16-HOT). Incubations of homogenates from these organs with α-linolenic acid yielded 16(S)-hydroperoxide (16-HPOT) as a predominant product. Targeted proteomic analyses of these tissues revealed the presence of several highly homologous isoforms of the putative "9S-lipoxygenase type 6". One of these isoenzymes (CsLOX3, an 877 amino acid polypeptide) was prepared by heterologous expression in E. coli and exhibited 16(S)- and 13(S)-lipoxygenase activity toward α-linolenic and linoleic acids, respectively. Furthermore, α-linolenate was a preferred substrate. The molecular structures of 16(S)-HOT and 16(S)-HPOT (Me or Me/TMS) were unequivocally confirmed by the mass spectral data, 1H-NMR, 2D 1H-1H-COSY, TOCSY, HMBC, and HSQC spectra, as well as enantiomeric HPLC analyses. Thus, the vegetative CsLOX3, biosynthesizing 16(S)-HPOT, is the first 16(S)-LOX and ω3-LOX ever discovered. Eicosapentaenoic and hexadecatrienoic acids were also specifically transformed to the corresponding ω3(S)-hydroperoxides by CsLOX3.

Computational Insights and In Silico Characterization of a Novel Mini-Lipoxygenase from Nostoc Sphaeroides and Its Application in the Quality Improvement of Steamed Bread

Lipoxygenase (EC1.13.11.12, LOX) has been potentially used in the food industry for food quality improvement. However, the low activity, poor thermal stability, narrow range of pH stability, as well as undesirable isoenzymes and off-flavors, have hampered the application of current commercial LOX. In this study, a putative mini-lipoxygenase gene from cyanobacteria, Nostoc sphaeroides (NsLOX), was cloned and expressed in E. coli BL21. NsLOX displayed only 26.62% structural identity with the reported LOX from Cyanothece sp., indicating it as a novel LOX. The purified NsLOX showed the maximum activity at pH 8.0 and 15 °C, with superior stability at a pH range from 6.0 to 13.0, retaining about 40% activity at 40 °C for 90 min. Notably, NsLOX exhibited the highest specific activity of 78,080 U/mg towards linoleic acid (LA), and the kinetic parameters-K_m, k_cat, and k_cat/K_m-attain values of 19.46 μM, 9199.75 s^-1, and 473.85 μM^-1 s^-1, respectively. Moreover, the activity of NsLOX was obviously activated by Ca²⁺, but it was completely inhibited by Zn²⁺ and Cu²⁺. Finally, NsLOX was supplied in steamed bread and contributed even better improved bread quality than the commercial LOX. These results suggest NsLOX as a promising substitute of current commercial LOX for application in the food industry.

Tea plant (Camellia sinensis) lipid metabolism pathway modulated by tea field microbe (Colletotrichum camelliae) to promote disease

Tea is one of the most popular healthy and non-alcoholic beverages worldwide. Tea anthracnose is a disease in tea mature leaves and ultimately affects yield and quality. Colletotrichum camelliae is a dominant fungal pathogen in the tea field that infects tea plants in China. The pathogenic factors of fungus and the susceptible factors in the tea plant are not known. In this work, we performed molecular and genetic studies to observe a cerato-platanin protein CcCp1 from C. camelliae, which played a key role in fungal pathogenicity. △CcCp1 mutants lost fungal virulence and reduced the ability to produce conidia. Transcriptome and metabolome were then performed and analysed in tea-susceptible and tea-resistant cultivars, Longjing 43 and Zhongcha 108, upon C. camelliae wild-type CCA and △CcCp1 infection, respectively. The differentially expressed genes and the differentially accumulated metabolites in tea plants were clearly overrepresented such as linolenic acid and linoleic acid metabolism, glycerophospholipid metabolism, phenylalanine biosynthesis and metabolism, biosynthesis of flavonoid, flavone and flavonol etc. In particular, the accumulation of jasmonic acid was significantly increased in the susceptible cultivar Longjing 43 upon CCA infection, in the fungal CcCp1 protein dependent manner, suggesting the compound involved in regulating fungal infection. In addition, other metabolites in the glycerophospholipid and phenylalanine pathway were observed in the resistant cultivar Zhongcha 108 upon fungal treatment, suggesting their potential role in defense response. Taken together, this work indicated C. camelliae CcCp1 affected the tea plant lipid metabolism pathway to promote disease while the lost function of CcCp1 mutants altered the fungal virulence and plant response.

Urate oxidase from tea microbe Colletotrichum camelliae is involved in the caffeine metabolism pathway and plays a role in fungal virulence

Tea is one of the most well-known, healthy beverages in the world. Tea plants produce caffeine as a secondary metabolite. Colletotrichum camelliae is one of the most important microbes frequently isolated from tea fields, and it causes anthracnose disease in tea plant. In the present work, we performed molecular microbiology and transcriptomic analyses of the C. camelliae - tea plant interaction to investigate the mechanism of fungal virulence and plant defense. Upon infection of tea plant with C. camelliae, we observed alterations in the expression of fungal transcripts, including those of many genes associated with caffeine metabolism, such as those encoding various transporters, xanthine dehydrogenase, and urate oxidase (UOX). In particular, the deletion of C. camelliae urate oxidase (CcUOX), which is involved in the caffeine metabolism pathway, reduced fungal tolerance to caffeine, and impaired fungal virulence. CcUOX is involved in caffeine metabolism by the degradation of uric acid contents. C. camelliaeΔCcUOX mutants impaired uric acid degradation in vivo. The CcUOX gene was cloned from C. camelliae, overexpressed in Escherichia coli, and the recombinant CcUOX protein displayed maximum activity at 30°C and a pH of 4.0. The recombinant CcUOX efficiently reduced uric acid in vitro suggesting a promising application in caffeine-contaminated environment management and in producing food with low purine contents to prevent uric acid related human diseases, such as hyperuricemia and gout.

Hormonal regulation of health-promoting compounds in tea (Camellia sinensis L.)

Tea is the most frequently consumed natural beverage across the world produced with the young leaves and shoots of the evergreen perennial plant Camellia sinensis (L.) O. Kuntze. The expanding global appeal of tea is partly attributed to its health-promoting benefits such as anti-inflammation, anti-cancer, anti-allergy, anti-hypertension, anti-obesity, and anti- SARS-CoV-2 activity. The many advantages of healthy tea intake are linked to its bioactive substances such as tea polyphenols, flavonoids (catechins), amino acids (theanine), alkaloids (caffeine), anthocyanins, proanthocyanidins, etc. that are produced through secondary metabolic pathways. Phytohormones regulate secondary metabolite biosynthesis in a variety of plants, including tea. There is a strong hormonal response in the biosynthesis of polyphenols, catechins, theanine and caffeine in tea under control and perturbed environmental conditions. In addition to the impact of preharvest plant hormone manipulation on green tea quality, changes in hormones of postharvest tea also regulate quality-related metabolites in tea. In this review, we discuss the health benefits of major tea constituents and the role of various plant hormones in improving the endogenous levels of these compounds for human health benefits. The fact that the ratio of tea polyphenols to amino acids and the concentrations of tea components are changed by environmental conditions, most notably by climate change-associated variables, the selection and usage of optimal hormone combinations may aid in sustaining tea quality, and thus can be beneficial to both consumers and producers.

Specific Roles of Lipoxygenases in Development and Responses to Stress in Plants

Lipoxygenases (LOXs), naturally occurring enzymes, are widely distributed in plants and animals. LOXs can be non-sulfur iron, non-heme iron, or manganese-containing dioxygenase redox enzymes. LOXs catalyze the oxidation of polyunsaturated fatty acids into fatty acid hydroperoxides. Linolenic acid, a precursor in the jasmonic acid (JA) biosynthesis, is converted to 12-oxo-phytodienoic acid through oxygenation with LOX, allene oxide synthase, and allene oxide cyclase. Moreover, JA participates in seed germination, fruit ripening, senescence, and many other physio-biochemical processes. LOXs also play crucial roles in defense responses against biotic stress, i.e., insects, pests, pathogenic attacks, and abiotic stress, such as wounding, UV-rays, extreme temperature, oxidative stress, and drought.

A novel inhibitor of the JA signaling pathway represses herbivore resistance in tea plants

The jasmonic acid (JA) signaling pathway plays a vital role in mediating plant resistance to herbivores. Tea plant (Camellia sinensis) is one of the most important woody cash crops in the world. Due to the lack of genetic transformation systems for tea plants, how the JA signaling pathway works in tea plants has not yet been determined. Now, with the development of cross-disciplines, chemical biology provides new means for analysing the JA signaling pathway. In the present study, the small molecule isoquinoline compound ZINC71820901 (lyn3) was obtained from the ZINC molecular library through virtual screening based on the structure of the crystal COI1-JAZ1 co-receptor and was found to act as an inhibitor of the JA signaling pathway both in Arabidopsis and tea plants. Our results revealed that lyn3 repressed tea plant resistance to Ectropis grisescens mainly by decreasing the accumulation of (-)-epicatechin (EC) and (-)-epigallocatechin (EGC) via repression of the JA signaling pathway, which functioned in the different modulation manner to the already known inhibitor SHAM. As a novel inhibitor of JA signaling pathway, lyn3 provides a specific option for further research on the JA pathway.

Evolution and functional diversity of lipoxygenase (LOX) genes in allotetraploid rapeseed (Brassica napus L.)

Lipoxygenase (LOX, EC 1.13.11.12) is a non-haeme iron-containing dioxygenase family that catalyzes the oxygenation of polyunsaturated fatty acids into bio-functionally fatty acid diverse (oxylipins) and plays vital role in plant growth and development and responses to abiotic and biotic stresses. Though LOX genes have been studied in many plant species, their roles in Brassicaceae species are still unknown. Here, a set of 14, 18, and 33 putative LOX genes were identified in Brassica rapa, Brassica oleracea and Brassica napus (allotetraploid rapeseed), respectively, which could be divided into 9-LOX (LOX1/5), 13-LOX type I (LOX3/4/6), and type II (LOX2) subgroups. There was an expansion of LOX2 orthologous genes in Brassicaceae. Most of the LOX genes are intron rich and conserved in gene structure, and the LOX proteins all have the conserved lipoxygenase and PLAT/LH2 domain. Ka/Ks ratio revealed that the majority of LOXs underwent purifying selection in Brassicaceae. The light-, ABA-, MeJA-related cis-elements and MYB-binding sites in the promoters of BnaLOXs were the most abundant. BnaLOXs displayed different spatiotemporal expression patterns and various abiotic/biotic stress responsive expression patterns. BnaLOX1/5 were slightly or no response to phytohormones and abiotic stresses. BnaLOX3/4/6 predominantly express in roots and were strongly up-regulated by salinity and PEG treatments, and BnaLOX3/4 were the methyl jasmonate (MeJA) and salicylic acid (SA) early response genes and strongly induced by infection of Sclerotinia sclerotiorum; while the BnaLOX2 members predominantly express in stamens, were MeJA and SA continuous response genes and strongly repressed by cold, heat and waterlogging treatments in leaves. Our results are useful for understanding the biological functions of the BnaLOX genes in allotetraploid rapeseed.

Indole primes defence signalling and increases herbivore resistance in tea plants

Upon herbivore attack, plants emit herbivore-induced plant volatiles (HIPVs). HIPVs can prime defences and resistance of intact plants. However, how HIPVs are decoded and translated into functional defence responses is not well understood, especially in long-lived woody plants. Here, we investigated the impact of the aromatic HIPV indole on defence-related early signalling, phytohormone accumulation, secondary metabolite biosynthesis and herbivore resistance in tea plants. We find that tea plants infested with tea geometrid caterpillars release indole at concentrations >450 ng*hr^-1 . Exposure to corresponding doses of synthetic indole primes the expression of early defence genes involved in calcium (Ca²⁺ ) signalling, MPK signalling and jasmonate biosynthesis. Indole exposure also primes the production of jasmonates and defence-related secondary metabolites. These changes are associated with higher herbivore resistance of indole-exposed tea plants. Chemical inhibition of Ca²⁺ and jasmonate signalling provides evidence that both are required for indole-mediated defence priming and herbivore resistance. Our systematic assessment of the impact of indole on defence signalling and deployment shows that indole acts by boosting Ca²⁺ signalling, resulting in enhanced jasmonate-dependent defence and resistance in a woody plant. Our work extends the molecular basis of HIPV-induced defence priming from annual plants to an economically important tree species.

Synthesis of 13R,20-dihydroxy-docosahexaenoic acid by site-directed mutagenesis of lipoxygenase derived from Oscillatoria nigro-viridis PCC 7112

Lipoxygenases (LOXs) are implicated in the biosynthesis of pro- and anti-inflammatory lipid mediators involved in immune cell signaling, most of which catalyze peroxidation of polyunsaturated fatty acids by distinct regio- and stereoselectivity. Current reports suggested that conserved amino acid, Gly in R-LOXs and Ala in S-LOXs, in the catalytic domain play an important role in determining the position as well as the stereochemistry of the functional group. Recently, we have confirmed that the catalytic specificity of cyanobacterial lipoxygenase, named Osc-LOX, with alanine at 296 was 13S-type toward linoleic acid, and producing a 17S- hydroxy-docosahexaenoic acid from docosahexaenoic acid (DHA). Here, we aimed to change the catalytic property of LOX from13S-LOX to 9R-LOX by replacing Ala with Gly and to produce a lipid mediators different from the wild-type using DHA. Finally, we succeeded in generating human endogenous a 13R-hydroxy-docosahexaenoic acid and a 13R,20-dihydroxy-docosahexaenoic acid from DHA through an enzymatic reaction using the Osc-LOX-A296G. Our study could enable physiological studies and pharmaceutical research for the 13R,20-dihydroxy-docosahexaenoic acid.

Physiological genetics, chemical composition, health benefits and toxicology of tea (Camellia sinensis L.) flower: A review

The flower of tea (Camellia sinensis L.) plant has been paid an increasing attention in the last twenty years, since it was found that tea flowers contained representative constituents similar to those of tea leaves, such as catechins, caffeine and amino acids. Tea flower is theoretically valuable although it has been considered as an industrial waste over a long period of time. This review summarizes the research findings conducted until now on physiological genetics, chemical composition, health benefits and toxicology of tea flowers, aiming to foresee their future applications. A lot of genes are involved in flower development and the synthesis and transmission of various chemicals in tea flowers. The chemical composition of tea flower consists mainly of catechins, polysaccharides, proteins, amino acids and saponins and thus tea flower possesses various health benefits such as antioxidant, anti-inflammatory, immunostimulating, antitumor, hypoglycemic, anti-obesity and anti-allergic activities. Moreover, tea flower contains a protease that can elevate the free amino acids content in the tea infusion by almost two folds. More importantly, the enzymatic activity of the protease is much higher than that of the commercially available proteases. Additionally, aqueous extracts of tea flower are demonstrated to safe to animals. Thus, the potential uses of tea flowers in food and medical fields are warranted.

Identification of alternatively spliced gene isoforms and novel noncoding RNAs by single-molecule long-read sequencing in Camellia

Direct single-molecule sequencing of full-length transcripts allows efficient identification of gene isoforms, which is apt to alternative splicing (AS), polyadenylation, and long non-coding RNA analyses. However, the identification of gene isoforms and long non-coding RNAs with novel regulatory functions remains challenging, especially for species without a reference genome. Here, we present a comprehensive analysis of a combined long-read and short-read transcriptome sequencing in Camellia japonica. Through a novel bioinformatic pipeline of reverse-tracing the split-sites, we have uncovered 257,692 AS sites from 61,838 transcripts; and 13,068 AS isoforms have been validated by aligning the short reads. We have identified the tissue-specific AS isoforms along with 6,373 AS events that were found in all tissues. Furthermore, we have analysed the polyadenylation (polyA) patterns of transcripts, and found that the preference for polyA signals was different between the AS and non-AS transcripts. Moreover, we have predicted the phased small interfering RNA (phasiRNA) loci through integrative analyses of transcriptome and small RNA sequencing. We have shown that a newly evolved phasiRNA locus from lipoxygenases generated 12 consecutive 21 bp secondary RNAs, which were responsive to cold and heat stress in Camellia. Our studies of the isoform transcriptome provide insights into gene splicing and functions that may facilitate the mechanistic understanding of plants.

Exogenous indole acetic acid alleviates Cd toxicity in tea (Camellia sinensis)

Cadmium (Cd), a toxic heavy metal, restrains the growth and development of plants and threatens global food safety. Many studies on the alleviation of heavy metal toxicity by exogenous phytohormones have emerged, but reports on tea (Camellia sinensis) are still scarce. In this study, the effects of indole acetic acid (IAA) (2 μM and 10 μM) on Cd uptake and on the physiological and biochemical characteristics of the 'Xiangfeicui' tea cultivar were investigated for the first time. The order of Cd accumulation in tea seedlings was root > stem > mature leaf > tender leaf. Under Cd stress (30 mg kg^-1), photosynthetic pigment levels, antioxidant enzyme activity, root vigor, root IAA content, and the levels of most metabolites (including caffeine, soluble sugar, total amino acids, some amino acid components, and most catechins) were significantly reduced, while levels of malondialdehyde, proline, epicatechin, and some amino acids increased. We therefore propose that by reducing Cd accumulation, exogenous IAA can lessen the adverse effects of Cd on the physiology and biochemistry of tea seedlings, promoting the growth of healthier tea plants.

Recombinant Lipoxygenases and Hydroperoxide Lyases for the Synthesis of Green Leaf Volatiles

Green leaf volatiles (GLVs) are mainly C₆- and in rare cases also C₉-aldehydes, -alcohols, and -esters, which are released by plants in response to biotic or abiotic stresses. These compounds are named for their characteristic smell reminiscent of freshly mowed grass. This review focuses on GLVs and the two major pathway enzymes responsible for their formation: lipoxygenases (LOXs) and fatty acid hydroperoxide lyases (HPLs). LOXs catalyze the peroxidation of unsaturated fatty acids, such as linoleic and α-linolenic acids. Hydroperoxy fatty acids are further converted by HPLs into aldehydes and oxo-acids. In many industrial applications, plant extracts have been used as LOX and HPL sources. However, these processes are limited by low enzyme concentration, stability, and specificity. Alternatively, recombinant enzymes can be used as biocatalysts for GLV synthesis. The increasing number of well-characterized enzymes efficiently expressed by microbial hosts will foster the development of innovative biocatalytic processes for GLV production.

Identification of candidate flowering and sex genes in white Guinea yam (D. rotundata Poir.) by SuperSAGE transcriptome profiling

Dioecy (distinct male and female individuals) and scarce to non-flowering are common features of cultivated yam (Dioscorea spp.). However, the molecular mechanisms underlying flowering and sex determination in Dioscorea are largely unknown. We conducted SuperSAGE transcriptome profiling of male, female and monoecious individuals to identify flowering and sex-related genes in white Guinea yam (D. rotundata), generating 20,236 unique tags. Of these, 13,901 were represented by a minimum of 10 tags. A total 88 tags were significantly differentially expressed in male, female and monoecious plants, of which 18 corresponded to genes previously implicated in flower development and sex determination in multiple plant species. We validated the SuperSAGE data with quantitative real-time PCR (qRT-PCR)-based analysis of the expression of three candidate genes.

We further investigated the flowering patterns of 1938 D. rotundata accessions representing diverse geographical origins over two consecutive years. Over 85% of accessions were either male or non-flowering, less than 15% were female, while monoecious plants were rare. Intensity of flowering varied between male and female plants, with the former flowering more abundantly than the latter. Candidate genes identified in this study can be targeted for further validation and to induce regular flowering in poor to non-flowering cultivars. Findings of the study provide important inputs for further studies aiming to overcome the challenge of flowering in yams and to improve efficiency of yam breeding.

Enhanced transcriptome responses in herbivore-infested tea plants by the green leaf volatile (Z)-3-hexenol

Green leaf volatiles (GLVs) play a vital role in enhancing herbivore-associated defense responses, but the mechanism by which they precisely regulate such responses is not well understood. (Z)-3-Hexenol (z3HOL), an important component of GLVs, effectively activates the defense of tea plants (Camellia sinensis) against a tea geometrid (TG) Ectropis obliqua Prout. To elucidate the molecular mechanisms of defense activation by z3HOL, RNA-Sequencing was employed to investigate the effect of z3HOL on transcriptome responses to TG in tea plants. A total of 318 upregulated genes were identified, and expression of 10 unigenes was validated by quantitative real-time PCR. Among these 318 upregulated genes, 56 were defense-related, including 6 key enzyme genes in jasmonic acid, and ethylene biosynthesis, 24 signal transduction genes, and 12 insect-responsive transcription factors. Most of the defense-related genes are induced by JA, TG, or wounding treatments, suggesting that JA signaling plays a vital role in z3HOL-induced tea defense against TG.

The involvement of a herbivore-induced acyl-CoA oxidase gene, CsACX1, in the synthesis of jasmonic acid and its expression in flower opening in tea plant (Camellia sinensis)

The biosynthesis of jasmonic acid (JA) in plant peroxisomes requires the action of acyl-CoA oxidase (ACX; EC 1.3.3.6). Multiple isoforms of ACXs have been identified in various annual herbaceous plants, but the genes encoding these enzymes in perennial woody plants are yet to be fully investigated. In this study, an ACX gene named CsACX1 (GeneBank accession: KX650077.1) was isolated from tea plant (Camellia sinensis L.). CsACX1 was predicted to consist of 664 amino acid residues. Transcriptional analysis revealed that CsACX1 can be induced by mechanical wounding, JA application, and infestation by the tea geometrid Ectropis obliqua Prout and the tea green leafhopper Empoasca (Matsumurasca) onukii Matsuda. To further elucidate the function of CsACX1, it was heterologously expressed in a bacterial system and characterized. Recombinant CsACX1 showed preference for C₁₂ ∼ C₁₆-CoA substrates. The constitutive expression of CsACX1 can rescue wound-related JA biosynthesis in Arabidopsis mutant acx1. CsACX1 was expressed in different organs, predominantly in flowers. Notably, CsACX1 transcripts were detected up-regulated during flower opening, and the JA levels were correlated with CsACX1 expression. All these results enrich our knowledge of the regulatory pathway involved in the JA biosynthesis in tea, and helps further understand the defense mechanism of tea plant against insects.

Validation of reference genes for gene expression studies in post-harvest leaves of tea plant (Camellia sinensis)

Tea is one of three major non-alcoholic beverages that are popular all around the world. The economic value of tea product largely depends on the post-harvest physiology of tea leaves. The utilization of quantitative reverse transcription polymerase chain reaction is a widely accepted and precise approach to determine the target gene expression of tea plants, and the reliability of results hinges on the selection of suitable reference genes. A few reliable reference genes have been documented using various treatments and different tissues of tea plants, but none has been done on post-harvest leaves during the tea manufacturing process. The present study selected and analyzed 15 candidate reference genes: Cs18SrRNA, CsGADPH, CsACT, CsEF-1α, CsUbi, CsTUA, Cs26SrRNA, CsRuBP, CsCYP, CselF-4α, CsMON1, CsPCS1, CsSAND, CsPPA2, CsTBP. This study made an assessment on the expression stability under two kinds of post-harvest treatment, turn over and withering, using three algorithms-GeNorm, Normfinder, and Bestkeeper. The results indicated that the three commonly used reference genes, CsTUA, Cs18SrRNA, CsRuBP, together with Cs26SrRNA, were the most unstable genes in both the turn over and withering treatments. CsACT, CsEF-1α, CsPPA2, and CsTBP were the top four reference genes in the turn over treatment, while CsTBP, CsPCS1, CsPPA2, CselF-4α, and CsACT were the five best reference genes in the withering group. The expression level of lipoxygenase genes, which were involved in a number of diverse aspects of plant physiology, including wounding, was evaluated to validate the findings. To conclude, we found a basis for the selection of reference genes for accurate transcription normalization in post-harvest leaves of tea plants.

Unraveling the Roles of Regulatory Genes during Domestication of Cultivated Camellia: Evidence and Insights from Comparative and Evolutionary Genomics

With the increasing power of DNA sequencing, the genomics-based approach is becoming a promising resolution to dissect the molecular mechanism of domestication of complex traits in trees. Genus Camellia possesses rich resources with a substantial value for producing beverage, ornaments, edible oil and more. Currently, a vast number of genetic and genomic research studies in Camellia plants have emerged and provided an unprecedented opportunity to expedite the molecular breeding program. In this paper, we summarize the recent advances of gene expression and genomic resources in Camellia species and focus on identifying genes related to key economic traits such as flower and fruit development and stress tolerances. We investigate the genetic alterations and genomic impacts under different selection programs in closely related species. We discuss future directions of integrating large-scale population and quantitative genetics and multiple omics to identify key candidates to accelerate the breeding process. We propose that future work of exploiting the genomic data can provide insights related to the targets of domestication during breeding and the evolution of natural trait adaptations in genus Camellia.

Stabilization and improved activity of arachidonate 11S-lipoxygenase from proteobacterium Myxococcus xanthus

Lipoxygenases (LOXs) catalyze the dioxygenation of PUFAs to produce regio- and stereospecific oxygenated fatty acids. The identification of regio- and stereospecific LOXs is important because their specific products are involved in different physiological activities in various organisms. Bacterial LOXs are found only in some proteobacteria and cyanobacteria, and they are not stable in vitro. Here, we used C20 and C22 PUFAs such as arachidonic acid (ARA), eicosapentaenoic acid, and docosahexaenoic acid to identify an 11S-specific LOX from the proteobacterium Myxococcus xanthus and explore its in vitro stability and activity. The activity and stability of M. xanthus ARA 11S-LOX as well as the production of 11S-hydroxyeicosatetraenoic acid from ARA were significantly increased by the addition of phosphatidylcholine, Ca²⁺, and coactosin-like protein (newly identified in the yeast Rhodosporidium toluroides) as stimulatory factors; in fact, LOX activity in the presence of all three factors increased approximately 3-fold. Our results indicate that these stimulatory factors can be used to increase the activity and stability of bacterial LOX and the production of bioactive hydroxy fatty acids, which can contribute to new academic research.

Characterization and Alternative Splicing Profiles of the Lipoxygenase Gene Family in Tea Plant (Camellia sinensis)

Oxylipins, including jasmonic acid (JA) and volatiles, are important for signaling in plants, and these are formed by the lipoxygenase (LOX) enzyme family. There is a large gap in understanding of the underlying molecular basis of their roles in tea plants. Here, we identified 11 CsLOX genes from the tea plant (Camellia sinensis), and characterized their phylogeny, gene structure and protein features into three subclasses. We then examined their enzymatic activities, LOX expression and alternative splicing of transcripts during development and in response to abiotic or biotic stresses in tea plants. In vitro expressed protein assays showed that the CsLOX2, 3 and 9 enzymatically function to produce 9/13-HPOT, 13-HPOT and 9-HPOT, respectively. CsLOX2 and CsLOX9 green fluorescent protein (GFP) fusion proteins localized to chloroplasts and the cytoplasm, respectively. RNA sequencing, quantitative reverse transcription-PCR and Northern blot analysis suggested that CsLOX5, 6 and 9 were predominantly expressed in seeds, flowers and roots, respectively. CsLOX2, 3, 4, 6 and 7 were up-regulated after attack by the insect Ectropis oblique, while CsLOX1 was induced after infection with the pathogen Glomerella cingulata. CsLOX3, 7 and 10 were up-regulated by JA but not ABA or salicylic acid. Long-term cold stress down-regulated CsLOX expression while a short duration of cold induced the expression of CsLOX1, 6 and 7. Alternatively spliced transcripts of six CsLOX genes were dynamically regulated through time and varied in relative abundances under the investigated stresses; we propose a mechanism of competing or compensating regulation between isoforms. This study improves our understanding of evolution of LOXs and regulation of their diverse functions in plants.

Two New Polyphenol Oxidase Genes of Tea Plant (Camellia sinensis) Respond Differentially to the Regurgitant of Tea Geometrid, Ectropis obliqua

Polyphenol oxidases (PPOs) have been reported to play an important role in protecting plants from attacks by herbivores. Though PPO genes in other plants have been extensively studied, research on PPO genes in the tea plant (Camellia sinensis) is lacking. In particular, which members of the PPO gene family elicit the defense response of the tea plant are as yet unknown. Here, two new PPO genes, CsPPO1 and CsPPO2, both of which had high identity with PPOs from other plants, were obtained from tea leaves. The full length of CsPPO1 contained an open reading frame (ORF) of 1740 bp that encoded a protein of 579 amino acids, while CsPPO2 contained an ORF of 1788 bp that encoded a protein of 595 amino acids. The deduced CsPPO1 and CsPPO2 proteins had calculated molecular masses of 64.6 and 65.9 kDa; the isoelectric points were 6.94 and 6.48, respectively. The expression products of recombinant CsPPO1 and CsPPO2 in Escherichia coli were about 91 and 92 kDa, respectively, but the recombinant proteins existed in the form of an inclusion body. Whereas CsPPO1 is highly expressed in stems, CsPPO2 is highly expressed in roots. Further results showed that the expression of CsPPO1 and CsPPO2 was wound- and Ectropis obliqua-induced, and that regurgitant, unlike treatment with wounding plus deionized water, significantly upregulated the transcriptional expression of CsPPO2 but not of CsPPO1. The difference between regurgitant and wounding indicates that CsPPO2 may play a more meaningful defensive role against E. obliqua than CsPPO1. Meanwhile, we found the active component(s) of the regurgitant elicited by the expression of CsPPO may contain small molecules (under 3-kDa molecular weight). These conclusions advance the understanding of the biological function of two new PPO genes and show that one of these, CsPPO2, may be a promising gene for engineering tea plants that are resistant to E. obliqua.

Regulation of lipid peroxidation and ferroptosis in diverse species

This review by Conrad et al. reviews the functions and regulation of lipid peroxidation, ferroptosis, and the antioxidant network in diverse species, including humans, other mammals and vertebrates, plants, invertebrates, yeast, bacteria, and archaea, and discusses the potential evolutionary roles of lipid peroxidation and ferroptosis.

Lipid peroxidation is the process by which oxygen combines with lipids to generate lipid hydroperoxides via intermediate formation of peroxyl radicals. Vitamin E and coenzyme Q₁₀ react with peroxyl radicals to yield peroxides, and then these oxidized lipid species can be detoxified by glutathione and glutathione peroxidase 4 (GPX4) and other components of the cellular antioxidant defense network. Ferroptosis is a form of regulated nonapoptotic cell death involving overwhelming iron-dependent lipid peroxidation. Here, we review the functions and regulation of lipid peroxidation, ferroptosis, and the antioxidant network in diverse species, including humans, other mammals and vertebrates, plants, invertebrates, yeast, bacteria, and archaea. We also discuss the potential evolutionary roles of lipid peroxidation and ferroptosis.

Transcriptomic analysis of flower development in tea (Camellia sinensis (L.))

Flowering is a critical and complicated process in plant development, involving interactions of numerous endogenous and environmental factors, but little is known about the complex network regulating flower development in tea plants. In this study, de novo transcriptome assembly and gene expression analysis using Illumina sequencing technology were performed. Transcriptomic analysis assembles gene-related information involved in reproductive growth of C. sinensis. Gene Ontology (GO) analysis of the annotated unigenes revealed that the majority of sequenced genes were associated with metabolic and cellular processes, cell and cell parts, catalytic activity and binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that metabolic pathways, biosynthesis of secondary metabolites, and plant hormone signal transduction were enriched among the DEGs. Furthermore, 207 flowering-associated unigenes were identified from our database. Some transcription factors, such as WRKY, ERF, bHLH, MYB and MADS-box were shown to be up-regulated in floral transition, which might play the role of progression of flowering. Furthermore, 14 genes were selected for confirmation of expression levels using quantitative real-time PCR (qRT-PCR). The comprehensive transcriptomic analysis presents fundamental information on the genes and pathways which are involved in flower development in C. sinensis. Our data also provided a useful database for further research of tea and other species of plants.

Melon13-lipoxygenase CmLOX18 may be involved in C6 volatiles biosynthesis in fruit

To better understand the function role of the melon CmLOX18 gene in the biosynthesis of C6 volatiles during fruit ripening, we biochemically characterized CmLOX18 and identified its subcellular localization in transgenic tomato plants. Heterologous expression in yeast cells showed that the molecular weight of the CmLOX18 protein was identical to that predicted, and that this enzyme possesseed lipoxygenase activity. Linoleic acid was demonstrated to be the preferred substrate for the purified recombinant CmLOX18 protein, which exhibited optimal catalytic activity at pH 4.5 and 30 °C. Chromatogram analysis of the reaction product indicated that the CmLOX18 protein exhibited positional specificity, as evidenced by its release of only a C-13 oxidized product. Subcellular localization analysis by transient expression in Arabidopsis protoplasts showed that CmLOX18 was localized to non-chloroplast organelles. When the CmLOX18 gene was transgenically expressed in tomato via Agrobacterium tumefaciens-mediated transformation, it was shown to enhance expression levels of the tomato hydroperoxide lyase gene LeHPL, whereas the expression levels of six TomLox genes were little changed. Furthermore, transgenic tomato fruits exhibited increases in the content of the C6 volatiles, namely hexanal, (Z)-3-hexanal, and (Z)-3-hexen-1-ol, indicating that CmLOX18 probably plays an important role in the synthesis of C6 compounds in fruits.

Does oolong tea (Camellia sinensis) made from a combination of leaf and stem smell more aromatic than leaf-only tea? Contribution of the stem to oolong tea aroma

The raw materials used to make oolong tea (Camellia sinensis) are a combination of leaf and stem. Oolong tea made from leaf and stem is thought to have a more aromatic smell than leaf-only tea. However, there is no available evidence to support the viewpoint. In this study, sensory evaluation and detailed characterization of emitted and internal volatiles (not readily emitted, but stored in samples) of dry oolong teas and infusions indicated that the presence of stem did not significantly improve the total aroma characteristics. During the enzyme-active processes, volatile monoterpenes and theanine were accumulated more abundantly in stem than in leaf, while jasmine lactone, indole, and trans-nerolidol were lower in stem than in leaf. Tissue-specific aroma-related gene expression and availability of precursors of aroma compounds resulted in different aroma distributions in leaf and stem. This study presents the first determination of the contribution of stem to oolong tea aroma.

Tea green leafhopper, Empoasca vitis, chooses suitable host plants by detecting the emission level of (3Z)-hexenyl acetate

Green leaf volatiles (GLVs) have been reported to play an important role in the host-locating behavior of several folivores that feed on angiosperms. However, next to nothing is known about how the green leafhopper, Empoasca vitis, chooses suitable host plants and whether it detects differing emission levels of GLV components among genetically different tea varieties. Here we found that the constitutive transcript level of the tea hydroperoxide lyase (HPL) gene CsiHPL1, and the amounts of (Z)-3-hexenyl acetate and of total GLV components are significantly higher in tea varieties that are susceptible to E. vitis (Enbiao (EB) and Banzhuyuan (BZY)) than in varieties that are resistant to E. vitis (Changxingzisun (CX) and Juyan (JY)). Moreover, the results of a Y-tube olfactometer bioassay and an oviposition preference assay suggest that (Z)-3-hexenyl acetate and (Z)-3-hexenol offer host and oviposition cues for E. vitis female adults. Taken together, the two GLV components, (Z)-3-hexenol and especially (Z)-3-hexenyl acetate, provide a plausible mechanism by which tea green leafhoppers distinguish among resistant and susceptible varieties. Future research should be carried out to obtain the threshold of the above indices and then assess their reasonableness. The development of practical detection indices would greatly improve our ability to screen and develop tea varieties that are resistant to E. vitis.

Decreased Biosynthesis of Jasmonic Acid via Lipoxygenase Pathway Compromised Caffeine-Induced Resistance to Colletotrichum gloeosporioides Under Elevated CO2 in Tea Seedlings

Caffeine, the major purine alkaloid in tea has long been known for its role in plant defense. However, its effect on Colletotrichum gloeosporioides that causes brown blight disease in tea is largely unknown especially under elevated CO₂. Here we show that elevated CO₂ reduced endogenous caffeine content in tea leaves, but sharply increased susceptibility of tea to C. gloeosporioides. The expression of C. gloeosporioides actin gene was gradually increased during the postinoculation period. In contrast, foliar application of caffeine decreased the C. gloeosporioides-induced necrotic lesions and the expression of C. gloeosporioides actin. Analysis of endogenous jasmonic acid (JA) content revealed that exogenous caffeine could induce JA content under both CO₂ conditions in absence of fungal infection; however, in presence of fungal infection, caffeine increased JA content only under elevated CO₂. Furthermore, exogenous caffeine enhanced lipoxygenase (LOX) activity and its biosynthetic gene expression under both CO₂ conditions, indicating that increased JA biosynthesis via LOX pathway by caffeine might strengthen plant defense only under elevated CO₂, while caffeine-induced defense under ambient CO₂ might be associated with JA-independent LOX pathway in tea. These results provide novel insights into caffeine-induced plant defense mechanisms that might help to develop an eco-friendly approach for disease control.

Mineral and metabolic profiles in tea leaves and flowers during flower development

Tea [Camellia sinensis (L.) O. Kuntze] is one of the most popular non-alcoholic beverage crops in the world, and the physiological processes and gene regulations involved in development in tea plants have been well characterized. However, relatively little is known about the metabolic changes combined with mineral distributions that occur during flower development. Here we detected the contents of 11 elements in tea leaves and flowers and found that, some of them, especially phosphorus, sulfur and copper, showed significant changes during tea flowering. We also detected 122 metabolites in tea leaves and flowers and found that, 72 of them showed significant differences between flowers and leaves, of which sugars, organic acids, and flavonoids dominated. The sugars, such as trehalose and galactose, all accumulated in tea flowers, and the organic acids, such as malic acid, citric acid and fumaric acid involved in TCA cycle. The flavonoids, like epicatechin, catechin gallate and epigallocatechin, were more abundant in leaves. Furthermore, we found that the contents of 33 metabolites changed during the development of flowers. Especially, citric acid, phenylalanine and most flavonoids decreased while fructose and galactose increased during flowering stages in flowers. We also analyzed the correlations between the ions and metabolites and found that, some mineral nutrients including phosphorus, sulfur, manganese and zinc had close relations to organic acids, flavonoids, sugars and several amino acids during flowering. We mapped the metabolic pathway according to the KEGG database. This work will serve as the foundation for a systems biology approach to the understanding of mineral metabolism.

Functional Characterization of 9-/13-LOXs in Rice and Silencing Their Expressions to Improve Grain Qualities

Lipoxygenases (LOXs) are involved in oxidative rancidity and render rice unsuitable for human consumption. Here, RNA interference- (RNAi-) induced gene expression inhibition was used to analyze the functions of the bran/seed-specific LOXs in rice. r9-LOX1 and L-2 (9-LOX category) were the candidate genes expressing a bran/seed-specific LOX, while RCI-1 was (13-LOX category) a plastid-specific LOX. Real-time PCR showed that three LOXs were cultivar/tissue specific expression on a certain level. r9-LOX1 and L-2 were generally much higher in active bran/seed than in stabilized bran, mature seed, and regenerated plant. RCI-1 was barely expressed in seed. In transgenic lines, r9-LOX1, as well as L-2, expression was dramatically downregulated, compared to the nontransgenic controls. SPME/GC-MS analysis of r9-LOX1 RNAi transgenic lines showed 74.33% decrease in nonanal content (formed during oxidation of linoleic acid by lipoxygenase), but 388.24% increase in acetic acid and 184.84% hexanal (direct products of 13-LOX). These results indicate that r9-LOX1 positively regulates the amount of nonanal but negatively regulates acetic acid and hexanal. The negative regulation may be due to a mechanism of negative feedback between LOX family members. The information will help comprehensively understand the function of the bran/seed-specific LOXs, r9-LOX1, and improve the storage quality in the future.

Heterologous Expression and Biochemical Characterization of Two Lipoxygenases in Oriental Melon, Cucumis melo var. makuwa Makino

Lipoxygenases (LOXs) are a class of non-heme iron-containing dioxygenases that catalyse oxidation of polyunsaturated fatty acids to produce hydroperoxidation that are in turn converted to oxylipins. Although multiple isoforms of LOXs have been detected in several plants, LOXs in oriental melon have not attracted much attention. Two full-length LOX cDNA clones, CmLOX10 and CmLOX13 which have been isolated from oriental melon (Cucumis melo var. makuwa Makino) cultivar “Yumeiren”, encode 902 and 906 amino acids, respectively. Bioinformatics analysis showed that CmLOX10 and CmLOX13 included all of the typical LOX domains and shared 58.11% identity at the amino acid level with each other. The phylogenetic analysis revealed that CmLOX10 and CmLOX13 were members of the type 2 13-LOX subgroup which are known to be involved in biotic and abiotic stress. Heterologous expression of the full-length CmLOX10 and truncated CmLOX13 in Escherichia coli revealed that the encoded exogenous proteins were identical to the predicted molecular weights and possessed the lipoxygenase activities. The purified CmLOX10 and CmLOX13 recombinant enzymes exhibited maximum activity at different temperature and pH and both had higher affinity for linoleic acid than linolenic acid. Chromatogram analysis of reaction products from the CmLOX10 and CmLOX13 enzyme reaction revealed that both enzymes produced 13S-hydroperoxides when linoleic acid was used as substrate. Furthermore, the subcellular localization analysis by transient expression of the two LOX fusion proteins in tobacco leaves showed that CmLOX10 and CmLOX13 proteins were located in plasma membrane and chloroplasts respectively. We propose that the two lipoxygenases may play different functions in oriental melon during plant growth and development.

Biotechnological advances in tea (Camellia sinensis [L.] O. Kuntze): a review

This article presents a comprehensive review on the success and limitations of biotechnological approaches aimed at genetic improvement of tea with a purpose to explore possibilities to address challenging areas. Tea is a woody perennial tree with a life span of more than 100 years. Conventional breeding of tea is slow and limited primarily to selection which leads to narrowing down of its genetic base. Harnessing the benefits of wild relatives has been negligible due to low cross-compatibility, genetic drag and undesirable alleles for low yield. Additionally, being a recalcitrant species, in vitro propagation of tea is constrained too. Nevertheless, maneuvering with tissue/cell culture techniques, a considerable success has been achieved in the area of micropropagation, somatic embryogenesis as well as genetic transformation. Besides, use of molecular markers, "expressomics" (transcriptomics, proteomics, metabolomics), map-based cloning towards construction of physical maps, generation of expressed sequenced tags (ESTs) have facilitated the identification of QTLs and discovery of genes associated with abiotic or biotic stress tolerance and agronomic traits. Furthermore, the complete genome (or at least gene space) sequence of tea is expected to be accessible in the near future which will strengthen combinational approaches for improvement of tea. This review presents a comprehensive account of the success and limitations of the biotechnological tools and techniques hitherto applied to tea and its wild relatives. Expectedly, this will form a basis for making further advances aimed at genetic improvement of tea in particular and of economically important woody perennials in general.

CYP74B24 is the 13-hydroperoxide lyase involved in biosynthesis of green leaf volatiles in tea (Camellia sinensis)

Green leaf volatiles (GLVs) are C6-aliphatic aldehydes/alcohols/acetates, and biosynthesized from the central precursor fatty acid 13-hydroperoxides by 13-hydroperoxide lyases (HPLs) in various plant species. While GLVs have been implicated as defense compounds in plants, GLVs give characteristic grassy note to a bouquet of aroma in green tea, which is manufactured from young leaves of Camellia sinensis. Here we identify three HPL-related genes from C. sinensis via RNA-Sequencing (RNA-Seq) in silico, and functionally characterized a candidate gene, CYP74B24, as a gene encoding tea HPL. Recombinant CYP74B24 protein heterologously expressed in Escherichia coli specifically produced (Z)-3-hexenal from 13-HPOT with the optimal pH 6.0 in vitro. CYP74B24 gene was expressed throughout the aerial organs in a rather constitutive manner and further induced by mechanical wounding. Constitutive expression of CYP74B24 gene in intact tea leaves might account for low but substantial and constitutive formation of a subset of GLVs, some of which are stored as glycosides. Our results not only provide novel insights into the biological roles that GLVs play in tea plants, but also serve as basis for the improvement of aroma quality in tea manufacturing processes.

Proteomic Analysis of Lonicera japonica Thunb. Immature Flower Buds Using Combinatorial Peptide Ligand Libraries and Polyethylene Glycol Fractionation

Lonicera japonica Thunb. flower is a well-known medicinal plant that has been widely used for the treatment of human disease. To explore the molecular mechanisms underlying the biological activities of L. japonica immature flower buds, a gel-free/label-free proteomic technique was used in combination with combinatorial peptide ligand libraries (CPLL) and polyethylene glycol (PEG) fractionation for the enrichment of low-abundance proteins and removal of high-abundance proteins, respectively. A total of 177, 614, and 529 proteins were identified in crude protein extraction, CPLL fractions, and PEG fractions, respectively. Among the identified proteins, 283 and 239 proteins were specifically identified by the CPLL and PEG methods, respectively. In particular, proteins related to the oxidative pentose phosphate pathway, signaling, hormone metabolism, and transport were highly enriched by CPLL and PEG fractionation compared to crude protein extraction. A total of 28 secondary metabolism-related proteins and 25 metabolites were identified in L. japonica immature flower buds. To determine the specificity of the identified proteins and metabolites for L. japonica immature flower buds, Cerasus flower buds were used, which resulted in the abundance of hydroxymethylbutenyl 4-diphosphate synthase in L. japonica immature flower buds being 10-fold higher than that in Cerasus flower buds. These results suggest that proteins related to secondary metabolism might be responsible for the biological activities of L. japonica immature flower buds.

Regulation of formation of volatile compounds of tea (Camellia sinensis) leaves by single light wavelength

Regulation of plant growth and development by light wavelength has been extensively studied. Less attention has been paid to effect of light wavelength on formation of plant metabolites. The objective of this study was to investigate whether formation of volatiles in preharvest and postharvest tea (Camellia sinensis) leaves can be regulated by light wavelength. In the present study, in contrast to the natural light or dark treatment, blue light (470 nm) and red light (660 nm) significantly increased most endogenous volatiles including volatile fatty acid derivatives (VFADs), volatile phenylpropanoids/benzenoids (VPBs), and volatile terpenes (VTs) in the preharvest tea leaves. Furthermore, blue and red lights significantly up-regulated the expression levels of 9/13-lipoxygenases involved in VFADs formation, phenylalanine ammonialyase involved in VPBs formation, and terpene synthases involved in VTs formation. Single light wavelength had less remarkable influences on formation of volatiles in the postharvest leaves compared with the preharvest leaves. These results suggest that blue and red lights can be promising technology for remodeling the aroma of preharvest tea leaves. Furthermore, our study provided evidence that light wavelength can activate the expression of key genes involved in formation of plant volatiles for the first time.

Does Enzymatic Hydrolysis of Glycosidically Bound Volatile Compounds Really Contribute to the Formation of Volatile Compounds During the Oolong Tea Manufacturing Process?

It was generally thought that aroma of oolong tea resulted from hydrolysis of glycosidically bound volatiles (GBVs). In this study, most GBVs showed no reduction during the oolong tea manufacturing process. β-Glycosidases either at protein or gene level were not activated during the manufacturing process. Subcellular localization of β-primeverosidase provided evidence that β-primeverosidase was located in the leaf cell wall. The cell wall remained intact during the enzyme-active manufacturing process. After the leaf cell disruption, GBV content was reduced. These findings reveal that, during the enzyme-active process of oolong tea, nondisruption of the leaf cell walls resulted in impossibility of interaction of GBVs and β-glycosidases. Indole, jasmine lactone, and trans-nerolidol were characteristic volatiles produced from the manufacturing process. Interestingly, the contents of the three volatiles was reduced after the leaf cell disruption, suggesting that mechanical damage with the cell disruption, which is similar to black tea manufacturing, did not induce accumulation of the three volatiles. In addition, 11 volatiles with flavor dilution factor ≥4(4) were identified as relatively potent odorants in the oolong tea. These results suggest that enzymatic hydrolysis of GBVs was not involved in the formation of volatiles of oolong tea, and some characteristic volatiles with potent odorants were produced from the manufacturing process.

Simultaneous silencing of five lipoxygenase genes increases the contents of α-linolenic and linoleic acids in tomato (Solanum lycopersicum L.) fruits

α-Linolenic and linoleic acids are essential fatty acids (EFAs) for humans and required for maintenance of optimal health, but they cannot be synthesized by the human body and must be obtained from dietary sources. Using TomloxC fragment, TomloxD fragment, and partial TomloxA sequence that is highly identical with TomloxB and TomloxE, a RNAi expression vector was constructed. The construct was used to transform tomato cotyledon explants with the Agrobacterium-mediated co-cultivation method. The real-time reverse transcription polymerase chain reaction analysis showed that the expression of TomloxA, TomloxB, TomloxC, TomloxD, and TomloxE in transgenic tomato plants was drastically repressed, which led to a marked decrease in the levels of lipoxygenase activity. Finally, higher accumulations of the endogenous α-linolenic and linoleic acids were detected in the transgenic tomato fruits, which were 1.65-3.99 and 2.91-4.98 times that of the non-transformed tomato fruits, respectively.

Prospecting sugarcane resistance to Sugarcane yellow leaf virus by genome-wide association

Using GWAS approaches, we detected independent resistant markers in sugarcane towards a vectored virus disease. Based on comparative genomics, several candidate genes potentially involved in virus/aphid/plant interactions were pinpointed. Yellow leaf of sugarcane is an emerging viral disease whose causal agent is a Polerovirus, the Sugarcane yellow leaf virus (SCYLV) transmitted by aphids. To identify quantitative trait loci controlling resistance to yellow leaf which are of direct relevance for breeding, we undertook a genome-wide association study (GWAS) on a sugarcane cultivar panel (n = 189) representative of current breeding germplasm. This panel was fingerprinted with 3,949 polymorphic markers (DArT and AFLP). The panel was phenotyped for SCYLV infection in leaves and stalks in two trials for two crop cycles, under natural disease pressure prevalent in Guadeloupe. Mixed linear models including co-factors representing population structure fixed effects and pairwise kinship random effects provided an efficient control of the risk of inflated type-I error at a genome-wide level. Six independent markers were significantly detected in association with SCYLV resistance phenotype. These markers explained individually between 9 and 14 % of the disease variation of the cultivar panel. Their frequency in the panel was relatively low (8-20 %). Among them, two markers were detected repeatedly across the GWAS exercises based on the different disease resistance parameters. These two markers could be blasted on Sorghum bicolor genome and candidate genes potentially involved in plant-aphid or plant-virus interactions were localized in the vicinity of sorghum homologs of sugarcane markers. Our results illustrate the potential of GWAS approaches to prospect among sugarcane germplasm for accessions likely bearing resistance alleles of significant effect useful in breeding programs.

Salicylhydroxamic acid (SHAM) negatively mediates tea herbivore-induced direct and indirect defense against the tea geometrid Ectropis obliqua

We investigated the effect of the SHAM treatment of tea plants on their induced defense on a tea geometrid (TG), Ectropis obliqua Prout. Treatment of tea leaves with SHAM reduced the performance of TG and TG-elicited level of the lipoxygenase gene CsiLOX1 and the putative allene oxide synthase gene CsiAOS1. The release of wound-induced green leaf volatiles (GLVs) and the expression of the hydroperoxide lyase (HPL) gene CsiHPL1 were also reduced by SHAM treatment. The negative effect of SHAM dramatically reduced the total hebivore-induced plant volatiles (HIPVs) and the attractiveness to the parasitoid wasp Apanteles sp. These results indicated that SHAM may negatively mediate tea defense response against TG by modulating the wound-induced emission of GLVs, the expression of genes involved in oxylipin pathway, and the emission of other HIPV compounds that mediate direct and indirect defenses.

Molecular cloning, functional characterization and transcriptional regulation of a 9-lipoxygenase gene from olive

A lipoxygenase (LOX) cDNA clone (Oep2LOX1) has been isolated from olive fruit (Olea europaea cv. Picual). The deduced amino acid sequence displayed significant similarity to known plant LOX1 sequences. Genomic Southern blot analysis suggests that only one copy of Oep2LOX1 is present in the olive genome. Linolenic acid was the preferred substrate for the recombinant Oep2LOX1, which produced almost exclusively 9-hydroperoxide when linolenic acid was used as substrate, whereas a mixture of 9- and 13-hydroperoxides in a ratio 4:1 was formed from linoleic acid. Expression levels were measured in different tissues of Picual and Arbequina cultivars, including the mesocarp and seed during development and ripening of olive fruit. The results showed that Oep2LOX1 transcript level is spatially and temporally regulated. Besides, the transcriptional regulation of the Oep2LOX1 gene in response to different abiotic stresses was also investigated. Temperature, light and wounding regulate Oep2LOX1 gene expression in olive fruit mesocarp. The physiological role of the Oep2LOX1 gene during olive fruit ripening and in the stress response is discussed.