Abstract:[Background] Bacterial wilt is a serious disease attacking Eucalyptus. Arbuscular mycorrhizal fungi (AMF) affect the resistance of Eucalyptus to bacterial wilt, the mechanism of which remains unclear. [Objective] To explore the responding mechanism of AMF of Eucalyptus grandis during the infection course of Ralstonia solanacearum. [Methods] In this study, the non-mycorrhizal root tissue and the Rhizophagus irregularis-colonized root tissue of E. grandis were sampled at the time points of 0, 24, 48, and 96 hour post inoculation (hpi) of R. solanacearum. The genes involved in the response of R. irregularis in E. grandis roots to R. solanacearum infection were screened and identified by transcriptome sequencing. [Results] Compared with the non-mycorrhizal root tissue, R. irregularis showed 3 382-5 989 differentially expressed genes at different time points of E. grandis infection by R. solanacearum. The number of specifically differentially expressed genes of R. irregularis in response to R. solanacearum infection gradually increased over the infection time. R. irregularis significantly enriched the genes involved in AMF symbiont growth, sporulation, and apoptosis signaling pathways and siderophores at 24 hpi. At 48 hpi, R. irregularis mainly improved the transmembrane transport and promoted the absorption and exchange of nutrients such as potassium and nitrogen. At 96 hpi, R. irregularis mainly regulated the redox reaction and the synthesis of antibacterial substances such as flavonoids. [Conclusion] The AMF of E. grandis mainly regulate the plant growth, enhance the niche and nutrient (such as nitrogen, potassium, and iron) competition, secrete antimicrobial substances, and activate the defense response to R. solanacearum infection. The identified genes provide resources and references for further deciphering the mechanism of AMF-Eucalyptus-R. solanacearum interaction.
