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Phytoalexins play a crucial role in plant immunity. However, the mechanism of how phytoalexin is primed by beneficial microorganisms against broad‐spectrum pathogens remains elusive. This study showed that Bacillus cereus AR156 could trigger ISR against broad‐spectrum disease. RNA‐sequencing and camalexin content assays showed that AR156‐triggered ISR can prime the accumulation of camalexin synthesis and secretion‐related genes. Moreover, it was found that AR156‐triggered ISR elevates camalexin accumulation by increasing the expression of camalexin synthesis genes upon pathogen infection. We observed that the priming of camalexin accumulation by AR156 was abolished in cyp71a13 and pad3 mutants. Further investigations reveal that in the wrky33 mutant, the ability of AR156 to prime camalexin accumulation is abolished, and the mediated ISR against the three pathogens is significantly compromised. Furthermore, PEN3 and PDR12, acting as camalexin transporters, participate in AR156‐induced ISR against broad‐spectrum pathogens differently. In addition, salicylic acid and JA/ET signalling pathways participate in AR156‐primed camalexin synthesis to resist pathogens in different forms depending on the pathogen. In summary, B. cereus AR156 triggers ISR against Botrytis cinerea, Pst DC3000 and Phytophthora capsici by priming camalexin synthesis. Our study provides deeper insights into the significant role of camalexin for AR156‐induced ISR against broad‐spectrum pathogens. Summary statement: Beneficial rhizobacterium AR156 triggered ISR by enhancing camalexin accumulation in Arabidopsis, with WRKY33 acting as a positive regulator. PEN3 and PDR12 are involved in AR156‐induced ISR. Salicylic acid and JA/ET signalling pathways participate in AR156‐primed camalexin synthesis to resist various pathogens. [ABSTRACT FROM AUTHOR]

Plant gray mold disease caused by necrotrophic pathogen Botrytis cinerea , has been a serious threat to many important crops. It is urgent and necessary to seek an effective and environmentally friendly control strategy to control grey mold disease during the crop production. Moreover, it is also urgently needed to clear understand how the strategy works. To screening an efficient biocontrol agent in control of gray mold disease caused by B. cinerea , one hundred strains, which have the potential in controlling plant diseases, were selected from our laboratory’s strain library, and employed to our research. The results in the study indicated that Bacillus velezensis could act as a potential and efficient biocontrol agent (BCA), and two B. velezensis strains 5YN8 and DSN012 were screened out with high antagonistic and hydrolase activity, which could significantly control pepper gray mold disease and promote the pepper growth. Further deeply study on biocontrol mechanism indicated that B. velezensis could suppress the growth and spore formation of B. cinerea by secreting some secondary metabolites or releasing numbers of volatile organic compounds (VOCs). In the other hand, we also found that B. velezensis could trigger plant basal immunity. The BCA could increase the expression of SA signal markers and plant defense related genes. It was able to induce hydrogen peroxide accumulation and plant related enzyme activities in leaves of pepper as well. This study provides another high-efficiency, and potential strategies for the biological control of gray mold disease. It is the first report of B. velezensis strain which can control gray mold disease, In addition, it is also the first to comprehensively illustrate how the strains can efficiently protect pepper from B. cinerea attacking. [ABSTRACT FROM AUTHOR]