L-Canavanine, a Root Exudate From Hairy Vetch (Vicia villosa) Drastically Affecting the Soil Microbial Community and Metabolite Pathways.

Hossein Mardani-Korrani,Shinichi Yamazaki,Takashi Motobayashi,Naoko Ohkama-Ohtsu,Rumi Kaida,Yosei Oikawa,Akifumi Sugiyama,Yuichi Aoki,Masaru Kobayashi,Yoshiharu Fujii,Masaru Nakayasu

doi:10.3389/fmicb.2021.701796

Abstract

L-Canavanine, a conditionally essential non-proteinogenic amino acid analog to L-arginine, plays important roles in cell division, wound healing, immune function, the release of hormones, and a precursor for the synthesis of nitric oxide (NO). In this report, we found that the L-canavanine is released into the soil from the roots of hairy vetch (Vicia villosa) and declines several weeks after growth, while it was absent in bulk proxy. Hairy vetch root was able to exudate L-canavanine in both pots and in vitro conditions in an agar-based medium. The content of the L-canavanine in pots and agar conditions was higher than the field condition. It was also observed that the addition of L-canavanine significantly altered the microbial community composition and diversity in soil. Firmicutes and Actinobacteria became more abundant in the soil after the application of L-canavanine. In contrast, Proteobacteria and Acidobacteria populations were decreased by higher L-canavanine concentration (500 nmol/g soil). Prediction of the soil metabolic pathways using PICRUSt2 estimated that the L-arginine degradation pathway was enriched 1.3-fold when L-canavanine was added to the soil. Results indicated that carbon metabolism-related pathways were altered and the degradation of nitrogen-rich compounds (i.e., amino acids) enriched. The findings of this research showed that secretion of the allelochemical L-canavanine from the root of hairy vetch may alter the soil microbial community and soil metabolite pathways to increase the survival chance of hairy vetch seedlings. This is the first report that L-canavanine acts as an allelochemical that affects the biodiversity of soil microbial community.

Highlights

Amino acids as a significant portion of the root exudates play key roles in shaping the rhizosphere microbial community structure (Hu et al, 2018; Canarini et al, 2019)
Our results indicated that L-canavanine is secreted from the hairy vetch roots into the rhizosphere soil in considerable amounts (Figure 1)
The changes in the L-canavanine content in the rhizosphere soil of hairy vetch were monitored over 4 weeks after germination and during the vegetative stage when plants were 7 cm, 10 cm, 15 cm, and 20 cm height (Figure 2)

Summary

Introduction

Amino acids as a significant portion of the root exudates play key roles in shaping the rhizosphere microbial community structure (Hu et al, 2018; Canarini et al, 2019). Rhizosphere amino acids often result from lysis and cellular efflux from plants and soil organisms or proteolysis of existing peptides. They primarily serve as carbon and nitrogen sources in the rhizosphere (Moe, 2013). Few amino acids have been isolated and identified as intermediate compounds of biological phenomena such as allelopathy (Araya et al, 2014) It may be because evaluating FAAs is challenging, since the concentration of FAAs available in plant roots and rhizosphere depends on many factors such as soil type (Cao et al, 2016), soil pH (Rothstein, 2010), temperature, elevation, and analytical methods (Young et al, 1974; Chen et al, 2015). In many cases FAAs are lost by leaching the soil solution (Raab et al, 1996) or during the analytical procedures

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