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.