KEGG pathway analysis of transcriptome and metabolome
The DEGs and DMs of the two groups under comparison (EI vs. EF and EICL vs. EFCL) were performed for the KEGG pathway enrichment analysis. The results showed that there were five common pathways in DEGs and DMs (EI vs. EF) before pathogen inoculation, in which ”arginine and proline metabolism” and ”cysteine and methionine metabolism” were both significantly enriched (Fig. 2a). After pathogen inoculation, there were 24 common KEGG pathways (EICL vs. EIFL) in the host, but only ”plant hormone signal transduction” was significantly enriched (Fig. 2b). These results suggested that plant hormone signaling might be an essential pathway for endophytes to enhance the host’s disease resistance.
Gene expressions, biosynthesis and roles verification of phytohormones
Both endophyte and pathogen significantly affected the content of JA, ET and Pip in A. sibiricum , and their interaction had significant effects on the content of ET and Pip (Table 2). In the JA synthesis pathway, endophytes induced 8 gene expressions before pathogen inoculation (Fig. 3) and significantly increased JA content ignore pathogen inoculation (Fig. 4a). In the ET synthesis pathway, endophytes upregulated ACS and ACO expression levels and significantly promoted 1-aminocyclopropane-1-carboxylate (ACC) and ET synthesis after pathogen inoculation (Table 1; Fig. 3 and 4b). Furthermore, endophytes induced ALD1 and FMO1 expression in the Pip synthesis pathway and promoted L-lysine and D-Pip synthesis after pathogen inoculation (Table 1; Fig. 3 and 4c).
The exogenous chemicals, pathogens, and their interaction significantly all affected DI (Table 2) The results of the phytohormones verification test show that compared to the control, ETH treatment significantly reduced the DI in EI and EF, while MeJA treatment significantly reduced disease symptoms in EF but had no significant effects in EI (Fig. 4d). Conversely, Pip treatment significantly reduced disease symptoms in EI but had no significant effects in EF. Moreover, SA treatment had no significant effect on the disease symptoms in EI and EF. These results suggested that endophytes might enhance the disease resistance of the host by promoting ET and JA accumulation.