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.