4 DISCUSSION
Plant roots are colonized by a large number of diverse microorganisms in the soil. Plant growth-promoting bacteria (PGPR) can survive in the plant rhizosphere, attach to the plant surface, and develop a symbiotic relationship with the plant, promoting plant growth and improving plant resistance to biotic and abiotic stress (De Zelicourt et al., 2013). ISR triggered by PGPRs is a vital mechanism for enhancing plant resistance to stress. The mechanism of ISR tended to vary in different PGPRs and different pathogens. For example, ISR signaling triggered by P. fluorescens WCS417r in A. thaliana requires JA/ET but not SA (Ton et al., 2001; Zamioudis and Pieterse, 2012). In contrast, some PGPRs induce ISR signaling via SA instead of JA/ET (Audenaert et al., 2002; Barriuso et al., 2008). it was found that plant growth–promoting rhizobacterium B. cereus AR156 triggered the ISR in A. thaliana by activating both SA and JA/ET signaling pathways in an NPR1-dependent manner, thereby enhancing plant resistance to PstDC3000 (Niu et al., 2011).
In this study, we showed that AR156 could induce ISR against different lifestyle pathogens, including fungi and bacteria, which was in accordance with the results of previous studies (Jiang et al., 2015; Jiang et al., 2020; Nie et al., 2019; Niu et al., 2011). Simultaneously, we discovered that AR156 triggers ISR against P. capsici (Figure 1). However, the mechanism of AR156-induced ISR resistance to different types of pathogens remains unclear.