In plants, high carbon flux is committed to the biosynthesis of phenylalanine, tyrosine, and tryptophan, owing to their roles not only in the production of proteins, but also as precursors to ...thousands of primary and specialized metabolites. The core plastidial pathways that supply the majority of aromatic amino acids (AAAs) have previously been described in detail. More recently, the discovery of cytosolic enzymes contributing to overall AAA biosynthesis, as well as the identification of intracellular transporters and the continuing elucidation of transcriptional and post-transcriptional regulatory mechanisms, have revealed the complexity of this intercompartmental metabolic network. Here, we review the latest breakthroughs in AAA production and use the newest findings to highlight both longstanding and newly developed questions.
In vivo, in vitro, and in silico analyses have increased our depth of understanding of the plastidial AAA biosynthetic pathway.A newly discovered cytosolic Phe biosynthetic pathway, and the presence of cytosolic Tyr biosynthetic enzymes in some plant species has revealed that AAA biosynthesis is a complex intercompartmental network.Characterization of transporters has answered questions about the physiological importance of the intracellular movement of AAAs.Transcriptional and post-transcriptional regulatory mechanisms are responsible for the tight control of carbon flux distribution into, and within, the AAA network.
In addition to being a vital component of proteins, phenylalanine is also a precursor of numerous aromatic primary and secondary metabolites with broad physiological functions. In plants ...phenylalanine is synthesized predominantly via the arogenate pathway in plastids. Here, we describe the structure, molecular players and subcellular localization of a microbial-like phenylpyruvate pathway for phenylalanine biosynthesis in plants. Using a reverse genetic approach and metabolic flux analysis, we provide evidence that the cytosolic chorismate mutase is responsible for directing carbon flux towards cytosolic phenylalanine production via the phenylpyruvate pathway. We also show that an alternative transcription start site of a known plastidial enzyme produces a functional cytosolic prephenate dehydratase that catalyzes the conversion of prephenate to phenylpyruvate, the intermediate step between chorismate mutase and phenylpyruvate aminotransferase. Thus, our results complete elucidation of phenylalanine biosynthesis via phenylpyruvate in plants, showing that this pathway splits from the known plastidial arogenate pathway at chorismate, instead of prephenate as previously thought, and the complete pathway is localized in the cytosol.
Between A.D. 200 and 1000, sponsorship at baptism evolved from a simple liturgical act into a mechanism for the creation of enduring relationships regarded as especially holy forms of kinship. ...Combining anthropological, historical, theological, and literary approaches, Joseph Lynch presents a comprehensive analysis of the origins and development in Western society of this "spiritual" kinship. Because of its solemnity and adaptability, such kinship gradually took its place alongside blood and marital ties as a fundamental part of medieval society, continuing to expand in high and late medieval Europe and to flourish even in modern times, particularly in Latin America.
Professor Lynch traces the liturgical practices and theological beliefs undergirding sponsorship and examines its social purposes, including sacralization of personal firendships, creation of client/patron reltionships, extension of marital taboos, provision of protectors for the young, fostering of trust among adults, and dissemination of religious instruction. In the process he offers a rich array of insights into the Church's role in the passage of Western society from antiquity to the Middle Ages.
Joseph H. Lynch is Professor of History and former Director of the Center for Medieval and Renaissance Studies at Ohio State University. He is author of Simoniacal Entry into Religious Life form 1000 to 1260: A Social, Economic and Legal Study (Ohio State).
Originally published in 1986.
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As sessile organisms, plants evolved elaborate metabolic systems that produce a plethora of specialized metabolites as a means to survive challenging terrestrial environments. Decades of research ...have revealed the genetic and biochemical basis for a multitude of plant specialized metabolic pathways. Nevertheless, knowledge is still limited concerning the selective advantages provided by individual and collective specialized metabolites to the reproductive success of diverse host plants. Here we review the biological functions conferred by various classes of plant specialized metabolites in the context of the interaction of plants with their surrounding environment. To achieve optimal multifunctionality of diverse specialized metabolic processes, plants use various adaptive mechanisms at subcellular, cellular, tissue, organ and interspecies levels. Understanding these mechanisms and the evolutionary trajectories underlying their occurrence in nature will ultimately enable efficient bioengineering of desirable metabolic traits in chassis organisms.Decades of research have identified the biochemical basis of many plant specialized metabolic pathways. This Review highlights the biological context of these pathways and how recent advances have extended the new frontiers of phytochemistry.
The riboflavin derivatives FMN and flavin adenine dinucleotide (FAD) are critical cofactors for wide-ranging biological processes across all kingdoms of life. Although it is well established that ...these flavins can be readily interconverted, in plants, the responsible catalysts and regulatory mechanisms remain poorly understood. Here, we report the cloning and biochemical characterization of an FAD synthetase encoded by the gene At5g03430, which we have designated AtFADS1 (A. thaliana FADS1). The catalytic properties of the FAD synthetase activity are similar to those reported for other FAD synthetases, except that we observed maximum activity with Zn2+ as the associated divalent metal cation. Like human FAD synthetase, AtFADS1 exists as an apparent fusion with an ancestral FAD pyrophosphatase, a feature that is conserved across plants. However, we detected no pyrophosphatase activity with AtFADS1, consistent with an observed loss of a key catalytic residue in higher plant evolutionary history. In contrast, we determined that algal FADS1 retains both FAD synthetase and pyrophosphatase activity. We discuss the implications, including the potential for yet-unstudied biologically relevant noncatalytic functions, and possible evolutionary pressures that have led to the loss of FAD pyrophosphatase activity, yet universal retention of an apparently nonfunctional domain in FADS of land plants.
Plants synthesize a diversity of volatile molecules that are important for reproduction and defense, serve as practical products for humans, and influence atmospheric chemistry and climate. Despite ...progress in deciphering plant volatile biosynthesis, their release from the cell has been poorly understood. The default assumption has been that volatiles passively diffuse out of cells. By characterization of a Petunia hybrida adenosine triphosphate–binding cassette (ABC) transporter, PhABCG1, we demonstrate that passage of volatiles across the plasma membrane relies on active transport. PhABCG1 down-regulation by RNA interference results in decreased emission of volatiles, which accumulate to toxic levels in the plasma membrane. This study provides direct proof of a biologically mediated mechanism of volatile emission.
The plant cuticle is the final barrier for volatile organic compounds (VOCs) to cross for release to the atmosphere, yet its role in the emission process is poorly understood. Here, using a ...combination of reverse-genetic and chemical approaches, we demonstrate that the cuticle imposes substantial resistance to VOC mass transfer, acting as a sink/concentrator for VOCs and hence protecting cells from the potentially toxic internal accumulation of these hydrophobic compounds. Reduction in cuticle thickness has differential effects on individual VOCs depending on their volatility, and leads to their internal cellular redistribution, a shift in mass transfer resistance sources and altered VOC synthesis. These results reveal that the cuticle is not simply a passive diffusion barrier for VOCs to cross, but plays the aforementioned complex roles in the emission process as an integral member of the overall VOC network.
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•Substrate availability in desired tissue and target subcellular localization is one of the major constraints of plant metabolic engineering.•Silent metabolism unexpectedly modifies ...targeted metabolites although it can sometimes have beneficial effects.•Complex hidden crosstalk between different metabolic pathways and networks might compromise metabolic outcomes.•Impaired metabolism of signaling molecules further increases complexity of metabolic crosstalk.
Metabolic engineering is embraced as a method to sustainably enhance production of valuable phytochemicals with beneficial properties. However, successful production of these compounds in plants is not always predictable even when the pathways are fully known, frequently due to the lack of comprehensive understanding of plant metabolism as a whole, and interconnections between different primary, secondary, and hormone metabolic networks. Here, we highlight critical hidden constraints, including substrate availability, silent metabolism, and metabolic crosstalk, that impair engineering strategies. We explore how these constraints have historically been manifested in engineering attempts and propose how modern advancements will enable future strategies to overcome these impediments.
The flavin cofactors FMN and FAD are required for a wide variety of biological processes, however, little is known about their metabolism. Here, we report the cloning and biochemical characterization ...of the Saccharomyces cerevisiae pyrophosphatase Fpy1p. Genetic and functional studies suggest that Fpy1p may play a key role in flavin metabolism and is the first-reported non-Nudix superfamily enzyme to display FAD pyrophosphatase activity. Characterization of mutant yeast strains found that deletion of fpy1 counteracts the adverse effects that are caused by deletion of flx1, a known mitochondrial FAD transporter. We show that Fpy1p is capable of hydrolyzing FAD, NAD(H), and ADP-ribose. The enzymatic activity of Fpy1p is dependent upon the presence of K+ and divalent metal cations, with similar kinetic parameters to those that have been reported for Nudix FAD pyrophosphatases. In addition, we report that the deletion of fpy1 intensifies the FMN-dependence of null mutants of the riboflavin kinase Fmn1p, demonstrate that fpy1 mutation abolishes the decreased fitness resulting from the deletion of the flx1 ORF, and offer a possible mechanism for the genetic interplay between fpy1, flx1 and fmn1.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Plants synthesize volatile organic compounds (VOCs) to attract pollinators and beneficial microorganisms, to defend themselves against herbivores and pathogens, and for plant-plant communication. In ...general, VOCs accumulate in and are emitted from the tissue of their biosynthesis. However, using biochemical and reverse genetic approaches, we demonstrate a new physiological phenomenon: inter-organ aerial transport of VOCs via natural fumigation. Before petunia flowers open, a tube-specific terpene synthase produces sesquiterpenes, which are released inside the buds and then accumulate in the stigma, potentially defending the developing stigma from pathogens. These VOCs also affect reproductive organ development and seed yield, which are previously unknown functions of terpenoid compounds.
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