Abstract

Chitosan, behaving as a potent biotic elicitor, can induce plant defense response with the consequent enhancement in phytoalexin accumulation. Accordingly, chitosan elicitation was conducted to promote the production of two phytoalexins, i.e. formononetin and calycosin (also known as health-promoting isoflavones), in Astragalus membranaceus hairy root cultures (AMHRCs). Compared with control, 12.45- and 6.17-fold increases in the yields of formononetin (764.19 ± 50.81 μg/g DW) and calycosin (611.53 ± 42.22 μg/g DW) were obtained in 34 day-old AMHRCs treated by 100 mg/L of chitosan for 24 h, respectively. Moreover, chitosan elicitation could cause oxidative burst that would induce the expression of genes (MPK3 and MPK6) related to mitogen-activated protein kinase signaling (MAPK) cascades, which contributed to the transcriptional activation of pathogenesis-related genes (β-1,3-glucanase, Chitinase, and PR-1) and eight biosynthesis genes involved in the calycosin and formononetin pathway. Overall, the findings in this work not only highlight a feasible chitosan elicitation practice to enhance the in vitro production of two bioactive isoflavones for nutraceutical and food applications, but also contribute to understanding the phytoalexin biosynthesis in response to chitosan elicitation.

Highlights

  • Astragalus membranaceus, belonging to the Leguminosae family, is an economically important medicinal and food plant mainly distributed in North China[1]

  • Isoflavones are considered as phytoalexins in leguminous plants that are strongly inducible and especially sensitive to pathogen and insect challenges[28]

  • Chitosan is able to elicit plant defense response via simulating the attacks of fungal pathogen, which can eventually result in the enhancement of phytoalexin biosynthesis[17]

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Summary

Introduction

Astragalus membranaceus, belonging to the Leguminosae family, is an economically important medicinal and food plant mainly distributed in North China[1]. Like most of leguminous plants, A. membranaceus root naturally contains a kind of typical phytoalexins i.e. isoflavones, among which formononetin (FO) and calycosin (CA) are two representative compounds associated with versatile health-promoting benefits as diverse as antioxidant, antiviral, anti-inflammatory, anti-fatigue, estrogenic, neuroprotective, and hematopoietic activities[1,4,5]. In this respect, A. membranaceus root extracts have been well recognized as functional foods/nutraceuticals according to the U.S Dietary Supplement Health and Education Act, which can be sold as over-the-counter dietary supplements at health food markets[6,7]. There is no study about chitosan modifying MAPK signaling cascades on the stimulation of phytoalexin biosynthesis in plant in vitro cultures

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