Integrated metabolomic and transcriptomic analysis reveals the regulatory mechanisms of flavonoid and alkaloid biosynthesis in the new and old leaves of Murraya tetramera Huang.

BACKGROUND: Murraya tetramera Huang is a traditional Chinese woody medicine. Its leaves contain flavonoids, alkaloids, and other active compounds, which have anti-inflammatory and analgesic effects, as well as hypoglycemic and lipid-lowering effects, and anti-tumor effects. There are significant differences in the content of flavonoids and alkaloids in leaves during different growth cycles, but the synthesis mechanism is still unclear. RESULTS: In April 2021, new leaves (one month old) and old leaves (one and a half years old) of M. tetramera were used as experimental materials to systematically analyze the changes in differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) with transcriptomics and metabolomics technology. This was done to identify the signaling pathways of flavonoid and alkaloid synthesis. The results showed that the contents of total alkaloids and flavonoids in old leaves were significantly higher than those in new leaves. Thirteen flavonoid compounds, three isoflavone compounds, and nineteen alkaloid compounds were identified, and 125 and 48 DEGs related to flavonoid and alkaloid synthesis were found, respectively. By constructing the KEGG (Kyoto Encyclopedia of Genes and Genomes) network of DEGs and DAMs, it was shown that the molecular mechanism of flavonoid biosynthesis in M. tetramera mainly focuses on the "flavonoid biosynthetic pathway" and the "flavonoid and flavonol biosynthetic pathway". Among them, p-Coumaryl alcohol, Sinapyl alcohol, Phloretin, and Isoquercitrin were significantly accumulated in old leaves, the up-regulated expression of CCR (cinnamoyl-CoA reductase) might promote the accumulation of p-Coumaryl alcohol, upregulation of F5H (ferulate-5-hydroxylase) might promote Sinapyl alcohol accumulation. Alkaloids, including indole alkaloids, pyridine alkaloids, imidazole alkaloids, and quinoline alkaloids, were significantly accumulated in old leaves, and a total of 29 genes were associated with these substances. CONCLUSIONS: These data are helpful to better understand the biosynthesis of flavonoids and alkaloids in M. tetramera and provide a scientific basis for the development of medicinal components in M. tetramera.

Chromosome-level genome assembly of Murraya paniculata sheds light on biosynthesis of floral volatiles.

BACKGROUND: Murraya paniculata (L.) Jack, commonly called orange jessamine in the family Rutaceae, is an important ornamental plant in tropical and subtropical regions which is famous for its strong fragrance. Although genome assemblies have been reported for many Rutaceae species, mainly in the genus Citrus, full genomic information has not been reported for M. paniculata, which is a prerequisite for in-depth genetic studies on Murraya and manipulation using genetic engineering techniques. Here, we report a high-quality chromosome-level genome assembly of M. paniculata and aim to provide insights on the molecular mechanisms of flower volatile biosynthesis. RESULTS: The genome assembly with a contig N50 of 18.25 Mb consists of 9 pseudomolecules and has a total length of 216.86 Mb. Phylogenetic analysis revealed that M. paniculata diverged from the common ancestor approximately 25 million years ago and has not undergone any species-specific whole genome duplication events. Genome structural annotation and comparative genomics analysis revealed that there are obvious differences in transposon contents among the genomes of M. paniculata and Citrus species, especially in the upstream regions of genes. Research on the flower volatiles of M. paniculata and C. maxima at three flowering stages revealed significant differences in volatile composition with the flowers of C. maxima lacking benzaldehyde and phenylacetaldehyde. Notably, there are transposons inserted in the upstream region of the phenylacetaldehyde synthase (PAAS) genes Cg1g029630 and Cg1g029640 in C. maxima, but not in the upstream region of three PAAS genes Me2G_2379, Me2G_2381, and Me2G_2382 in M. paniculata. Our results indicated that compared to the low expression levels of PAAS genes in C. maxima, the higher expression levels of the three PAAS genes in M. paniculata are the main factor affecting the phenylacetaldehyde biosynthesis and causing the content difference of phenylacetaldehyde. The phenylacetaldehyde synthetic activities of the enzymes encoded by M. paniculata PAAS genes were validated by in vitro analyses. CONCLUSIONS: Our study provides useful genomic resources of M. paniculata for further research on Rutaceae plants, identifies new PAAS genes, and provides insights into how transposons contribute to variations in flower volatiles among Murraya and Citrus plants.

Molecular differentiation of the Murraya paniculata Complex (Rutaceae: Aurantioideae: Aurantieae).

BACKGROUND: Orange jasmine has a complex nomenclatural history and is now known as Murraya paniculata (L.) Jack. Our interest in this common ornamental stemmed from the need to resolve its identity and the identities of closely related taxa as hosts of the pathogen 'Candidatus Liberibacter asiaticus' and its vector Diaphorina citri. Understanding these microbe-vector-plant relationships has been hampered by taxonomic confusion surrounding Murraya at both the generic and specific levels. RESULTS: To resolve the taxonomic uncertainty, six regions of the maternally-inherited chloroplastal genome and part of the nuclear-encoded ITS region were amplified from 85 accessions of Murraya and Merrillia using the polymerase chain reaction (PCR). Clustering used maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI). Chronograms were produced for molecular dating, and to test the monophyly of Murraya rigorously, using selected accessions of Murraya and 26 accessions of the Rutaceae and Simarubaceae. Sequence data from the ITS and chloroplastal regions suggest that Murraya paniculata (sensu (Swingle WT and Reece CR, The Citrus Industry, p. 190-430, 1967)) can be separated into four distinct but morphologically somewhat cryptic taxa: Murraya paniculata (sensu (Mabberley DJ, Taxon 65:366-371, 2016)), M. elongata, M. sumatrana and M. lucida. In addition, Murraya omphalocarpa was identified as a putative hybrid of M. paniculata and M. lucida with two geographically isolated nothovarieties representing reciprocal crosses. Murraya is monophyletic, and molecular dating suggests that it diverged from Merrillia during the Miocene (23-5 Ma) with this Murraya group speciating and dispersing during the Middle Miocene onwards. CONCLUSIONS: The accessions from Asia and Australasia used in this study grouped into biogeographical regions that match herbarium specimen records for the taxa that suggest natural allopatric distributions with limited overlap and hybridity. Murraya paniculata has been distributed around the world as an ornamental plant. The division of the Murraya paniculata complex into four species with a rare hybrid also confirms morphological studies.

Transcriptomic insight into terpenoid and carbazole alkaloid biosynthesis, and functional characterization of two terpene synthases in curry tree (Murraya koenigii).

Curry tree (Murraya koenigii L.) is a rich source of aromatic terpenes and pharmacologically important carbazole alkaloids. Here, M. koenigii leaf transcriptome was generated to gain insight into terpenoid and alkaloid biosynthesis. Analysis of de novo assembled contigs yielded genes for terpene backbone biosynthesis and terpene synthases. Also, gene families possibly involved in carbazole alkaloid formation were identified that included polyketide synthases, prenyltransferases, methyltransferases and cytochrome P450s. Further, two genes encoding terpene synthases (MkTPS1 and MkTPS2) with highest in silico transcript abundance were cloned and functionally characterized to determine their involvement in leaf volatile formation. Subcellular localization using GFP fusions revealed the plastidial and cytosolic localization of MkTPS1 and MkTPS2, respectively. Enzymatic characterization demonstrated the monoterpene synthase activity of recombinant MkTPS1, which produced primarily (-)-sabinene from geranyl diphosphate (GPP). Recombinant MkTPS2 exhibited sesquiterpene synthase activity and formed (E,E)-α-farnesene as the major product from farnesyl diphosphate (FPP). Moreover, mRNA expression and leaf volatile analyses indicated that MkTPS1 accounts for (-)-sabinene emitted by M. koenigii leaves. Overall, the transcriptome data generated in this study will be a great resource and the start point for characterizing genes involved in the biosynthetic pathway of medicinally important carbazole alkaloids.

Analysis of whole chloroplast genomes from the genera of the Clauseneae, the curry tribe (Rutaceae, Citrus family).

The Clauseneae (Aurantioideae, Rutaceae) is a tribe in the Citrus family that, although economically important as it contains the culinary and medicinally-useful curry tree (Bergera koenigii), has been relatively understudied. Due to the recent significant taxonomic changes made to this tribe, a closer inspection of the genetic relationships among its genera has been warranted. Whole genome skimming was used to generate chloroplast genomes from six species, representing each of the four genera (Bergera, Clausena, Glycosmis, Micromelum) in the Clauseneae tribe plus one closely related outgroup (Merrillia), using the published plastome sequence of Citrus sinensis as a reference. Phylogenetically informative character (PIC) data were analyzed using a genome alignment of the seven species, and variability frequency among the species was recorded for each coding and non-coding region, with the regions of highest variability identified for future phylogenetic studies. Non-coding regions exhibited a higher percentage of variable characters as expected, and the phylogenetic markers ycf1, matK, rpoC2, ndhF, trnS-trnG spacer, and trnH-psbA spacer proved to be among the most variable regions. Other markers that are frequently used in phylogenetic studies, e.g. rps16, atpB-rbcL, rps4-trnT, and trnL-trnF, proved to be far less variable. Phylogenetic analyses of the aligned sequences were conducted using Bayesian inference (MrBayes) and Maximum Likelihood (RAxML), yielding highly supported divisions among the four genera.

[A new taxonomic system of the genus Murraya (Rutaceae) based on integration of morphology-based taxonomy and chemotaxonomy; and a philological survey on M. exotica in view of the relationship between Okinawa and China].

This review concerns the taxonomic status of the genus Murraya in tribe Clausenae, subfamily Aurantioideae, family Rutaceae, and presents a new system integrating both morphology-based taxonomy and chemotaxonomy. This genus has been morphologically divided into the sects Murraya and Bergera. This dichotomy is justified by the noticeable difference of secondary metabolites with 3-prenylindoles in Murraya and carbazoles in Bergera. As for other metabolites of genus Murraya, coumarins are found in both sects, but differ clearly in types; 8-prenylcoumarins occur throughout the sect Murraya whereas geranylated furocoumarins are known from some species of the sect Bergera. As far as chemical properties are concerned, sect Bergera is much closer to genus Clausena than sect Murraya, suggesting the dichotomy of genus Murraya to be generic rather than sectional. 8-Prenylcoumarins characterizing sect Murraya play a decisive role in the distinction of M. exotica from M. paniculata that occurs most widely in subtropical and tropical Asia and is well known for morphologic as well as chemical diversity. Though the morphological difference between the two species is slight only in leaves and leaflets, the distinction is well substantiated by the following chemical feature: 7-OMe-8-prenylcoumarins occur in M. exotica whereas 5,7-di-OMe-8-prenylcoumarins in M. paniculata. Sect Murraya has a very close relation to genus Merrillia that is chemically characterized by similar types of 8-prenylcoumarins, and is also related to a certain extent to genus Micromelum. M. exotica is philologically surveyed in view of the delicate relationships between Okinawa, the only habitat of this plant in Japan, and China in order to clarify its historical background.

Genetic relationships among wild and cultivated accessions of curry leaf plant (Murraya koenigii (L.) Spreng.), as revealed by DNA fingerprinting methods.

Murraya koenigii (L.) Spreng. (Rutaceae), is an aromatic plant and much valued for its flavor, nutritive and medicinal properties. In this study, three DNA fingerprinting methods viz., random amplification of polymorphic DNA (RAPD), directed amplification of minisatellite DNA (DAMD), and inter-simple sequence repeat (ISSR), were used to unravel the genetic variability and relationships across 92 wild and cultivated M. koenigii accessions. A total of 310, 102, and 184, DNA fragments were amplified using 20 RAPD, 5 DAMD, and 13 ISSR primers, revealing 95.80, 96.07, and 96.73% polymorphism, respectively, across all accessions. The average polymorphic information content value obtained with RAPD, DAMD, and ISSR markers was 0.244, 0.250, and 0.281, respectively. The UPGMA tree, based on Jaccard's similarity coefficient generated from the cumulative (RAPD, DAMD, and ISSR) band data showed two distinct clusters, clearly separating wild and cultivated accessions in the dendrogram. Percentage polymorphism, gene diversity (H), and Shannon information index (I) estimates were higher in cultivated accessions compared to wild accessions. The overall high level of polymorphism and varied range of genetic distances revealed a wide genetic base in M. koenigii accessions. The study suggests that RAPD, DAMD, and ISSR markers are highly useful to unravel the genetic variability in wild and cultivated accessions of M. koenigii.