Bacillus amyloliquefaciens PMB05 increases resistance to bacterial wilt by activating MAPK and ROS pathway crosstalk in Arabidopsis thaliana

Bacterial wilt caused by Ralstonia solanacearum can infect many crops, causing significant losses worldwide. The use of beneficial Microorganisms is considered a feasible method for controlling this disease. Our previous study has shown that Bacillus amyloliquefaciens PMB05 can control Bacterial wilt through intensifying immune signals triggered by a PAMP from R. solanacearum. It is still uncertain whether induction of the mitogen-activated protein kinase (MAPK) pathway during PAMP-triggered immunity (PTI) is responsible for enhancing disease resistance. To gain more insights on how the presence of PMB05 regulates PTI signaling, its association with the MAPK pathway was assayed. Our results showed that the activation of MPK3/6 and expression of wrky22 upon treatment with the PAMP, PopW, was increased during co-treatment with PMB05. Moreover, the disease resistance conferred by PMB05 to Bacterial wilt was abolished in mekk1, mkk5, and mpk6 mutants. To determine the relationship between the MAPK pathway and plant immune signals, the assay on Reactive Oxygen Species (ROS) generation and callose deposition showed that only the ROS generation was strongly reduced in these mutants. Since ROS generation is highly correlated with RbohD, results revealed that effects of PMB05 on both PopW-induced ROS generation and disease resistant to Bacterial wilt were eliminated in the rbohD mutant, suggesting the generation of ROS is also required for PMB05-enhanced disease resistance. Taken together, we concluded that the crosstalk between the initiation of ROS generation and further activation of the MAPK pathway is necessary when PMB05 is used to improve disease resistance to Bacterial wilt.