Succession of endophytic fungi and arbuscular mycorrhizal fungi associated with the growth of plant and their correlation with secondary metabolites in the roots of plants

Abstract

Background: To decipher the root and microbial interaction, secondary metabolite accumulation in roots and the microbial community's succession model during the plant's growth period demands an in-depth investigation. However, till now, no comprehensive study is available on the succession of endophytic fungi and arbuscular mycorrhizal fungi (AMF) with roots of medicinal licorice plants and the effects of endophytic fungi and AMF on the secondary metabolite accumulation in licorice plant's root.

Results: In the current study, interaction between root and microbes in 1-3 years old medicinal licorice plant's root and rhizospheric soil was investigated. Secondary metabolites content in licorice root was determined using high-performance liquid chromatography (HPLC). The composition and diversity of endophytic and AMF in the root and soil were deciphered using high-throughput sequencing technology. During the plant's growth period, as compared to AMF, time and species significantly affected the diversity and richness of endophytic fungi, such as Ascomycota, Basidiomycota, Fusarium, Cladosporium, Sarocladium. The growth period also influenced the AMF diversity, evident by the significant increase in the relative abundance of Glomus and the significant decrease in the relative abundance of Diversispora. It indicated a different succession pattern between the endophytic fungal and AMF communities. Meanwhile, distance-based redundancy analysis and Mantel tests revealed root's water content and secondary metabolites (glycyrrhizic acid, liquiritin, and total flavonoids), which conferred endophytic fungi and AMF diversity. Additionally, plant growth significantly altered soil's physicochemical properties, which influenced the distribution of endophytic fungal and AMF communities.

Conclusions: This study indicated a different succession pattern between the endophytic fungal and AMF communities. During the plant's growth period, the contents of three secondary metabolites in roots increased per year, which contributed to the overall differences in composition and distribution of endophytic fungal and AMF communities. The endophytic fungal communities were more sensitive to secondary metabolites than AMF communities. The current study provides novel insights into the interaction between rhizospheric microbes and root exudates.

Keywords: Arbuscular mycorrhizal fungi; Endophytic fungi; High-throughput sequencing; Medicinal licorice; Plant growth; Secondary metabolites.

Fig. 1

Secondary metabolites content in the root of three licorices species changed with the growth period. Description: Bar charts (mean with standard error) with different lower-case letters represented a significant difference (P < 0.05) was assessed by one-way analysis of variance followed by Bonferroni’s statistic test for multiple comparisons. The same letter indicates no significant difference (P > 0.05). Abbreviations: GIA, GTF and LI mean glycyrrhizic acid, liquiritin and total flavonoid, respectively

Fig. 2

An analysis of Alpha diversity indices based on Wilcoxon rank-sum test. Description: The * represented a significant difference (p < 0.05) assessed by Wilcoxon rank-sum test for analysis. Ordinate is Alpha diversity index (Shannon index and ACE index), where (a) (b) represents the endophytic fungal community and (c) (d) represents the AMF community. Abscissa is the group name (E, R and S: years 1, 2, and 3, respectively; W, G and D: Glycyrrhiza uralensis, Glycyrrhiza glabra, and Glycyrrhiza inflata, respectively)

Fig. 3

Beta diversity analysis of endophytic fungal community based on weighted UniFrac distance. Description: (a) Non-Metric Multi-Dimensional Scaling (NMDS) analysis, which each point in the diagram represents a sample, and samples from the same group are represented in the same color. The lower Stress (< 0.2) indicates that NMDS can accurately reflect the degree of difference between samples. (b) The significance test of the differences of Beta diversity, which the * represented a significant difference (p < 0.05) assessed by Wilcoxon rank-sum test for analysis. Ordinate is the Beta diversity; abscissa is the group name that has identical meanings as described in Fig. 2

Fig. 4

Distribution difference of AMF community. Description: The petal diagram (a) and Venn diagram (b) based on operational taxonomic units (OTU), which represent common or unique OTUs to a given group. Group name has identical meanings as described in Fig. 2. The Principal Co-ordinates Analysis (PCoA) plot based on weighted unifrac distances for year 1, 2, 3 group (c), which each point in the diagram represents a sample, and samples from the same group are represented in the same color

Fig. 5

Histograms of relative abundance of the top 10 endophytic fungi at the phylum (a) level of taxonomy and at the genera (b) level of taxonomy. Description: (a) and (b) Ordinate both are the relative abundance of species, others mean less or not annotated; abscissa is the group name that has identical meanings as described in Fig. 2

Fig. 6

Histograms of relative abundance of the top 10 arbuscular mycorrhizal fungi phylum (a) and genera (b). Description: Abscissa is the relative abundance of species; others mean less or not annotated; Ordinate is the group name that has identical meanings as described in Fig. 2

Fig. 7

Linear discriminant analysis effect size (Lefse) analysis of differences in AMF community composition as a function of growth period. Description: In cladograms, the circle radiating from inside to outside represents the taxonomic level from the Phylum to the species. Each small circle at a different taxonomic level represents microbial groups that were significantly enriched in the corresponding groups and that significantly influenced the differences between groups, and the diameter of the small circle is proportionate to the relative abundance of species. Light yellow small circle represents microbial groups with no significant differences. Group name that has identical meanings as described in Fig. 2

Fig. 8

Relationship between secondary metabolites and soil physical and chemical properties and microbial community. Description: Heat maps of spearman correlation analysis between the top 20 OTUs, secondary metabolite and soil properties with (a) corresponding to Endophytic fungal community and (c) corresponding to AMF community, respectively. The mark * is significance test p < 0.05. Db-RDA analysis based on OTU levels that mainly used to reflect the relationship between microorganisms and environmental factors. Endophytic fungal community and AMF community corresponding to (b) (d), respectively