Distinct Mechanisms of Biotic and Chemical Elicitors Enable Additive Elicitation of the Anticancer Phytoalexin Glyceollin I

Abstract

Phytoalexins are metabolites biosynthesized in plants in response to pathogen, environmental, and chemical stresses that often have potent bioactivities, rendering them promising for use as therapeutics or scaffolds for pharmaceutical development. Glyceollin I is an isoflavonoid phytoalexin from soybean that exhibits potent anticancer activities and is not economical to synthesize. Here, we tested a range of source tissues from soybean, in addition to chemical and biotic elicitors, to understand how to enhance the bioproduction of glyceollin I. Combining the inorganic chemical silver nitrate (AgNO3) with the wall glucan elicitor (WGE) from the soybean pathogen Phytophthora sojae had an additive effect on the elicitation of soybean seeds, resulting in a yield of up to 745.1 µg gt−1 glyceollin I. The additive elicitation suggested that the biotic and chemical elicitors acted largely by separate mechanisms. WGE caused a major accumulation of phytoalexin gene transcripts, whereas AgNO3 inhibited and enhanced the degradation of glyceollin I and 6″-O-malonyldaidzin, respectively.

Elicitor and Receptor Molecules: Orchestrators of Plant Defense and Immunity

“…For instance, the oligosaccharides elicitors from M. grisea triggered phytoalexins synthesis in rice cells as the specific host and not in soybean cotyledon cells [107]. In contrast, β-glucan elicitors from Phytophthora sojae are able to activate defense responses in rice, soybean, and other non-hosts [109,110]. For example, a 75-kDa protein associated with the plasma membrane of Glycine max and Phaseolus vulgaris binds β-glucan elicitors from Phytophthora sp with high affinity.…”

Acidity stress for the systemic elicitation of glyceollin phytoalexins in soybean plants

“…20 The critical barriers that limit the accessibility of glyceollins are that they cannot be synthesized economically [21][22][23] or obtained in sufficient amounts from soybean tissues. [24][25][26] Efforts to improve accessibility have included (semi)synthesis, [21][22][23] fermentation of soybeans, 27 combined treatments of soybean seeds with pathogens and malting, 26 pathogens and environment stress, 28 and pathogens and chemicals. 25 A combined treatment of P. sojae WGE and the inorganic chemical silver nitrate had an additive effect, eliciting 1.5-fold more glyceollin I than the WGE treatment alone.…”

“…[24][25][26] Efforts to improve accessibility have included (semi)synthesis, [21][22][23] fermentation of soybeans, 27 combined treatments of soybean seeds with pathogens and malting, 26 pathogens and environment stress, 28 and pathogens and chemicals. 25 A combined treatment of P. sojae WGE and the inorganic chemical silver nitrate had an additive effect, eliciting 1.5-fold more glyceollin I than the WGE treatment alone. 25 Yet, overexpressing the isoflavonoid biosynthesis gene encoding IFR increased glyceollin amounts more than 3-fold, 29 demonstrating that bioengineering can provide greater enhancements in glyceollin yields.…”

Structure, Chemical Analysis, Biosynthesis, Metabolism, Molecular Engineering, and Biological Functions of Phytoalexins

“…These compounds have been the subject of numerous studies over the last two decades. Thirteen research and review articles have been published in this special issue: four articles concern the biosynthesis of phytoalexins as a response to biotic and/or abiotic elicitors capable of inducing their production in plants [ 1 , 2 , 3 , 4 ], two articles describe methods for phytoalexin analysis in complex matrices [ 5 , 6 ], one article reports on phytoalexin metabolism by fungi [ 7 ], and six articles focus on the biological activity of phytoalexins [ 8 , 9 , 10 , 11 , 12 , 13 ].…”

“…The elicitor-mediated increases of the SA and ABA pathways in pea resulted in a strong induction of the biosynthesis of the phytoalexin pisatin. In the article of Farrell et al [ 2 ], two distinct elicitors were also used to enhance the production of glyceollin I, a phytoalexin from soybean. Combination of the chemical elicitor, silver nitrate (AgNO 3 ) with the wall glucan elicitor (WGE) from the pathogen Phytophthora sojae was shown to have an additive effect on the induction of glyceollin production in soybean, reaching up to 745 µg/g tissue.…”