Pharmaceutically significant secondary metabolites or phytopharmaceuticals include alkaloids, glycosides, flavonoids, volatile oils, tannins, resins etc. Currently, most of these secondary metabolites are isolated from wild or cultivated plants because their chemical synthesis is either extremely difficult or economically infeasible. Biotechnological production in plant cell cultures is an attractive alternative, but to date this has had only limited commercial success because of a lack of understanding of how these metabolites are synthesized. Plants and/or plant cells in vitro, show physiological and morphological responses to microbial, physical or chemical factors which are known as ‘elicitors’. Elicitation is a process of induced or enhanced synthesis of secondary metabolites by the plants to ensure their survival, persistence and competitiveness. Here, we discuss the classification of elicitors, their mechanism of action, and applications for the production of phyto-pharmaceuticals from medicinal plants.

Plant cell elicitation for production of secondary metabolites: A review

Fungi are an understudied, biotechnologically valuable group of organisms. Due to 
the immense range of habitats that fungi inhabit, and the consequent need to compete against a diverse array of other fungi, bacteria, and animals, fungi have developed numerous survival mechanisms. The unique attributes of fungi thus herald great promise for their application in biotechnology and industry. Moreover, fungi can be grown with relative ease, making production at scale viable. The search for fungal biodiversity, and the construction of a living fungi collection, both have incredible economic potential in locating organisms with novel industrial uses that will lead to novel products. This manuscript reviews fifty ways in which fungi can potentially be utilized as biotechnology. We provide notes and examples for each potential exploitation and give examples from our own work and the work of other notable researchers. We also provide a flow chart that can be used to convince funding bodies of the importance of fungi for biotechnological research and as potential products. Fungi have provided the world with penicillin, lovastatin, and other globally significant medicines, and they remain an untapped resource with enormous industrial potential.

The amazing potential of fungi: 50 ways we can exploit fungi industrially

Production of the anticancer drug taxol in Taxus baccata suspension cultures: A review

Elicitation is a good strategy to induce physiological changes and stimulate defense or stress-induced responses in plants. The elicitor treatments trigger the synthesis of phytochemical compounds in fruits, vegetables and herbs. These metabolites have been widely investigated as bioactive compounds responsible of plant cell adaptation to the environment, specific organoleptic properties of foods, and protective effects in human cells against oxidative processes in the development of neurodegenerative and cardiovascular diseases and certain types of cancer. Biotic (biological origin), abiotic (chemical or physical origin) elicitors and phytohormones have been applied alone or in combinations, in hydroponic solutions or sprays, and in different selected time points of the plant growth or during post-harvest. Understanding how plant tissues and their specific secondary metabolic pathways respond to specific treatments with elicitors would be the basis for designing protocols to enhance the production of secondary metabolites, in order to produce quality and healthy fresh foods.

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Elicitation: A Tool for Enriching the Bioactive Composition of Foods

Catharanthus roseus is still the only source for the powerful antitumour drugs vinblastine and vincristine. Some other pharmaceutical compounds from this plant, ajmalicine and serpentine are also of economical importance. Although C. roseus has been studied extensively and was subject of numerous publications, a full characterization of its alkaloid pathway is not yet achieved. Here we review some of the recent work done on this plant. Most of the work focussed on early steps of the pathway, particularly the discovery of the 2-C-methyl-d-erythritol 4-phosphate (MEP)-pathway leading to terpenoids. Both mevalonate and MEP pathways are utilized by plants with apparent cross-talk between them across different compartments. Many genes of the early steps in Catharanthus alkaloid pathway have been cloned and overexpressed to improve the biosynthesis. Research on the late steps in the pathway resulted in cloning of several genes. Enzymes and genes involved in indole alkaloid biosynthesis and various aspects of their localization and regulation are discussed. Much progress has been made at alkaloid regulatory level. Feeding precursors, growth regulators treatments and metabolic engineering are good tools to increase productivity of terpenoid indole alkaloids. But still our knowledge of the late steps in the Catharanthus alkaloid pathway and the genes involved is limited.

https://link.springer.com/content/pdf/10.1007%2Fs11101-006-9047-8.pdf

Catharanthus terpenoid indole alkaloids: biosynthesis and regulation

Plants show physiological and morphological responses to a range of physical and chemical factors known as 'elicitors'. These responses have been considered as defence reactions 'elicited' by the plants' biochemical factory to ensure their survival, persistence and competitiveness. Recently examples have been cited of elicitation in some fungal and bacterial cultures. Through a chronological survey, this Review considers examples of elicitors and elicitation and describes suggested mechanisms of elicitation in plants and microbial cell cultures. The majority of research in this field has been carried out on the plant systems using complex (undefined) biotic elicitors. Carbohydrates are the main class of compounds used as defined elicitors. This Review focuses on carbohydrates as compounds initiating a defence response in cell cultures. Physiological changes brought about on the plant and microbial cultures include expression of novel metabolites and overproduction of already known products. Recent reports confirming elicitation in microbial cultures are of potential importance, as the relative ease of fermentation and scale-up could open an opportunity for the introduction of useful novel metabolites as well as enhancement of commercially useful bioproducts. In this context, a sound knowledge of the elicitor molecules' structure-function relationships and mechanisms of elicitation is essential.

Elicitation of plants and microbial cell systems.

The cyanobacterial circadian clock is an extensive regulator of gene expression, generating a 24-hour rhythm in the majority of genes in Synechococcus elongatus PCC 7942. This raises the question of how the cyanobacterial clock regulates, and receives input from, the diverse cellular processes it controls. Alternative sigma factors, which bind to the core RNA polymerase enzyme and direct the synthesis of specific sets of transcripts, are one mechanism for the clock to set the time of its outputs. In this work, we use single-cell time-lapse microscopy to reveal the transcriptional dynamics of RpoD4, an alternative sigma factor that was previously reported as either arrhythmic or circadian. We find instead that RpoD4 pulses at cell division, dynamics missed by previous bulk averaging. The circadian clock modulates the amplitude of RpoD4 expression pulses, as well as the timing of pulses through its control of division timing. In turn, a rpoD4 mutation causes a reduction in clock period. Further, a rpoD4 mutant results in smaller cell size, and increasing expression of RpoD4 results in larger cell sizes in a dose-response manner, allowing tunable control of cell size. Thus, our single-cell analysis has revealed pulsing gene expression dynamics in cyanobacteria, linking the clock, RpoD4 and the cell cycle.

/pdf/the-alternative-sigma-factor-rpod4-pulses-at-division-and-1onydo3u.pdf

Teresa Saez

Papers

Elicitation of plants and microbial cell systems.

The alternative sigma factor RpoD4 pulses at division and links the clock and the cell cycle in Synechococcus elongatus