Phytochemistry Reviews (v.15, #3)

The Amaryllidaceae alkaloids: biosynthesis and methods for enzyme discovery by Matthew B. Kilgore; Toni M. Kutchan (317-337).
Amaryllidaceae alkaloids are an example of the vast diversity of secondary metabolites with great therapeutic promise. The identification of novel compounds in this group with over 300 known structures continues to be an area of active study. The recent identification of norbelladine 4′-O-methyltransferase (N4OMT), an Amaryllidaceae alkaloid biosynthetic enzyme, and the assembly of transcriptomes for Narcissus sp. aff. pseudonarcissus and Lycoris aurea highlight the potential for discovery of Amaryllidaceae alkaloid biosynthetic genes with new technologies. Recent technical advances of interest include those in enzymology, next generation sequencing, genetic modification, nuclear magnetic resonance spectroscopy, and mass spectrometry.
Keywords: Galanthamine; Haemanthamine; Mass spectrometry; Next generation sequencing; Nuclear magnetic resonance spectroscopy

There has been remarkable progress in the discovery of specialized metabolism pathways in the past few years. This has largely been due to the advent of inexpensive high throughput sequencing technologies, improved gene annotation methods and the development of tools for testing candidate genes for their involvement in particular biosynthetic pathways. This review describes the recent discoveries made on new steps in monoterpenoid indole alkaloid (MIA) biosynthesis within Catharanthus roseus. The review also places these discoveries in context of the existing literature on regulation and production of MIAs in whole plants compared to cell and organ cultures.
Keywords: Monoterpenoid indole alkaloids; Catharanthus roseus; Transcriptomics; Targeted virus induced gene silencing; Pathway discovery/regulation/engineering

Methoxylated flavones: occurrence, importance, biosynthesis by Anna Berim; David R. Gang (363-390).
Lipophilic flavones with several methoxyl residues occur in various clades of land plants, from liverworts to core eudicots. Their chemodiversity is mediated by the manifold combinations of oxygenation and methoxylation patterns. In the Lamiaceae, Asteraceae, and Rutaceae, (poly)methoxylated flavones are thought to be produced by secretory tissues and stored externally or in oil cavities. They exhibit an array of bioactivities in vitro and in vivo, and may constitute part of the plants’ chemical defense mechanisms and represent promising natural lead molecules for the development of potent antiproliferative, antidiabetic, or anti-inflammatory drugs. The biosynthesis of (poly)methoxylated flavones in sweet basil (Ocimum basilicum L.) has been largely elucidated in the past few years. The knowledge obtained in those studies can be used for enzymatic semi-synthesis of these flavones as well as for further cell biological and physiological studies of basil trichome metabolism. In addition, these findings create an excellent starting point for investigations into (poly)methoxylated flavone metabolism in more and less distantly related taxa, which would shed light on the evolution of this biosynthetic capacity.
Keywords: Flavonoids; Lipophilic; O-methylation; Bioactivity; Biosynthetic network

Soybean isoflavonoids: role of GmMYB176 interactome and 14-3-3 proteins by Arun Kumaran Anguraj Vadivel; Arjun Sukumaran; Xuyan Li; Sangeeta Dhaubhadel (391-403).
Isoflavonoids are a group of plant natural compounds that are synthesized through a legume-specific branch of the phenylpropanoid pathway. They play numerous roles in plant–microbe interactions including inducers of nitrogen fixation and defense response in plants. Consumption of a soy-rich diet containing isoflavonoids has been noted for several health and nutritional benefits in humans and animals. Therefore, there are continuous efforts geared towards generating soybean cultivars with increased amount of isoflavonoids. However, isoflavonoid content is a complex polygenic trait that is influenced by multiple factors including genotype, environment, and the interaction between genotype and environment. In this review, we present the factors that regulate isoflavonoid content in soybean and discuss in detail the recent development on identifying the genetic factors that impact isoflavonoid synthesis and accumulation in soybean.
Keywords: Isoflavonoids; Soybean; MYB transcription factors; 14-3-3 Proteins; Gene regulation

Phenolic compounds in fruits and beverages consumed as part of the mediterranean diet: their role in prevention of chronic diseases by Yolanda Aguilera; Maria Angeles Martin-Cabrejas; Elvira González de Mejia (405-423).
The objective of this review was to assess, based on human data, the role of phenolic compounds in selected plant foods consumed as part of the Mediterranean diet in the prevention of chronic diseases (CDs) like cardiovascular disease, cancer and neurodegenerative conditions. Fruits and vegetables are rich sources of phenolic compounds and based on scientific data it would be expected that their consumption, as part of the diet, would be responsible for their documented preventive role of chronic diseases. The results of the review of scientific literature on human clinical trials revealed that in some studies polyphenols exert a positive effect in the prevention of cardiovascular disease, essentially blood pressure and arterial dilation, certain types of cancer and neurodegenerative disorders. However, such effects are not consistent with other clinical studies in which no effect has been found. Therefore, the level of evidence for a beneficial effect in humans of phenols on the prevention of CDs is weak and need to be strengthened by additional studies addressing potential confounding factors, such as interaction of phenols with other bioactive substances in foods and potential pro-oxidant effects.
Keywords: Anthocyanins; Blood pressure; Caffeoyl derivatives; Cardiovascular disease; Flavanols

The chemistry of gut microbial metabolism of polyphenols by Jan F. Stevens; Claudia S. Maier (425-444).
Gut microbiota contribute to the metabolism of dietary polyphenols and affect the bioavailability of both the parent polyphenols and their metabolites. Although there is a large number of reports of specific polyphenol metabolites, relatively little is known regarding the chemistry and enzymology of the metabolic pathways utilized by specific microbial species and taxa, which is the focus of this review. Major classes of dietary polyphenols include monomeric and oligomeric catechins (proanthocyanidins), flavonols, flavanones, ellagitannins, and isoflavones. Gut microbial metabolism of representatives of these polyphenol classes can be classified as A- and C-ring cleavage (retro Claisen reactions), C-ring cleavage mediated by dioxygenases, dehydroxylations (decarboxylation or reduction reactions followed by release of H2O molecules), and hydrogenations of alkene moieties in polyphenols, such as resveratrol, curcumin, and isoflavones (mediated by NADPH-dependent reductases). The qualitative and quantitative metabolic output of the gut microbiota depends to a large extent on the metabolic capacity of individual taxa, which emphasizes the need for assessment of functional analysis in conjunction with determinations of gut microbiota compositions.
Keywords: Catabolism; Flavonoid; Gut microbiota; Mechanism; Metabolic pathway

Mass spectrometry imaging for plant biology: a review by Berin A. Boughton; Dinaiz Thinagaran; Daniel Sarabia; Antony Bacic; Ute Roessner (445-488).
Mass spectrometry imaging (MSI) is a developing technique to measure the spatio-temporal distribution of many biomolecules in tissues. Over the preceding decade, MSI has been adopted by plant biologists and applied in a broad range of areas, including primary metabolism, natural products, plant defense, plant responses to abiotic and biotic stress, plant lipids and the developing field of spatial metabolomics. This review covers recent advances in plant-based MSI, general aspects of instrumentation, analytical approaches, sample preparation and the current trends in respective plant research.
Keywords: Biochemistry; Lateral resolution; Natural products; Spatial mapping; Spatial metabolomics

The elucidation of pathways leading to the signature metabolites accumulated in aromatic and medicinal plants has traditionally been fairly slow in comparison to progress made with much simpler microbes, where gene clustering for natural product biosynthesis is very common. However, recent advances in next-generation sequencing and innovative new approaches to gene discovery have narrowed this gap, and the elucidation of even complex plant pathways has now become significantly faster. A wealth of sequence data has been generated with aromatic and medicinal plants, and it has become increasingly difficult for researchers to stay abreast of new developments. In this review article, I will summarize the functionality of currently available genomics databases and will comment on future needs to maximize their utility.
Keywords: Aromatic plant; Database; Medicinal plant; Genome; Transcriptome; Metabolome; Bioinformatics