Armillaria mellea Symbiosis Drives Metabolomic and Transcriptomic Changes in Polyporus umbellatus Sclerotia.

Yong-Mei Xing,Yang Li,Shun-Xing Guo,Shu-Chao Yin,Liu Liu,Juan Chen,Bing Li,Shu-Xue Yin

doi:10.3389/fmicb.2021.792530

Abstract

Sclerotia, the medicinal part of Polyporus umbellatus, play important roles in diuresis and renal protection, with steroids and polysaccharides as the main active ingredients. The sclerotia grow and develop only after symbiosis with Armillaria sp. In this study, a systematic metabolomics based on non-targeted UPLC-MS method was carried out between the infected part of the separated cavity wall of the sclerotia (QR) and the uninfected part (the control group, CK) to find and identify differential metabolites. The biosynthetic pathway of characteristic steroids in sclerotia of P. umbellatus was deduced and the content of ergosterol, polyporusterone A and B in the QR and CK groups were detected with the High Performance Liquid Chromatography (HPLC). Furthermore, the expression patterns of putative genes associated with steroid biosynthesis pathway were also performed with quantitative real-time PCR. The results showed that a total of 258 metabolites originated from fungi with the fragmentation score more than 45 and high resolution mass were identified, based on UPLC-MS metabolomic analysis, and there were 118 differentially expressed metabolites (DEMs) between both groups. The metabolic pathways indicated that steroids, fatty acid and carbohydrate were active and enriched during P. umbellatus sclerotia infected by A. mellea. The content of ergosterol, polyporusterone A and B in the QR group increased by 32.2, 75.0, and 20.0%, in comparison to that of the control group. The qRT-PCR analysis showed that series of enzymes including C-8 sterol isomerase (ERG2), sterol C-24 methyltransferase (ERG6) and sterol 22-desaturase (ERG5), which played important roles in the final steps of ergosterol biosynthesis, all presented up-regulated patterns in the QR group in P. umbellatus. The comprehensive metabolomic and transcriptomic information will contribute to further study concerning the mechanisms of P. umbellatus sclerotial formation infected by A. mellea in the future.

Highlights

Polyporus umbellatus (Pers.) Fr. is a traditional medicinal fungus with sclerotia possessing diuretic, antitumor and renal protection acitivity
It had been well documented that the sugar content containing polysaccharides and glucose in the A. mellea infected part of P. umbellatus sclerotia was higher than that of the part without A. mellea infection (Guo et al, 2002). These results indicated that the differential metabolites present in the QR and the control parts might be different during A. mellea’s infection to P. umbellatus sclerotia and affect the composition of the metabolites residing in the medicinal fungus
P. umbellatus sclerotia can be generated only after it is co-cultured with A. mellea

Summary

Introduction

Polyporus umbellatus (Pers.) Fr. is a traditional medicinal fungus with sclerotia possessing diuretic, antitumor and renal protection acitivity. P. umbellatus sclerotia grow inside the soil while its edible fruiting bodies germinate from the sclerotia and turn up above the ground (Xing et al, 2011). Armillaria mellea is one of the species present in P. umbellatus sclerotia and it must form a symbiotic relationship and the sclerotia will grow and develop normally. A. mellea provides nutrition to sclerotia and at the same time, the rhizomorphs branches in the separated cavity and constructs a relatively stable relationship with P. umbellatus sclerotia, with the wall of the separated cavity only containing P. umbelltus sclerotial tissue while inside the separated cavity, there are A. mellea rhizomorphs and sclerotia (Guo and Xu, 1992, 1993; Guo et al, 2011; Xing et al, 2011)

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