Bacillus subtilis PTA-271 has been shown to induce ISR against the necrotroph Botrytis cinerea (Verhagen et al., 2011) and the hemibiotroph Neofusicoccum parvum (Trotel-Aziz et al., 2019) in grapevine. However, the mechanisms by which the bacterium activates the host's immune response underlying ISR remain to be elucidated. In this study, we examined whether the extent of priming state could contribute to the PTA-271-induced ISR in Arabidopsis, by focusing on the camalexin response and CYP71A12 gene expression after B. cinerea and Pst DC3000 infection. Our data provide evidence that PTA-271 triggers ISR against both pathogens through priming camalexin synthesis in SA-and NPR1-dependent manner. This response was further compromised in pad3 mutant after pathogen infection, highlighting that camalexin plays a prominent role in B. subtilis-ISR against both necrotroph and hemibiotroph.