Bacillus cereus AR156 primes induced systemic resistance by suppressing miR825/825 and activating defense-related genes in Arabidopsis

Small RNAs play an important role in plant immune responses. However, their regulatory function in induced systemic resistance(ISR) is nascent. Bacillus cereus AR156 is a plant growth-promoting rhizobacterium that induces ISR in Arabidopsis against bacterial infection. Here,by comparing small RNA profiles of Pseudomonas syringae pv. tomato(Pst) DC3000-infected Arabidopsis with and without AR156 pretreatment, we identified a group of Arabidopsis micro RNAs(mi RNAs) that are differentially regulated by AR156 pretreatment. mi R825 and mi R825 are two mi RNA generated from a single mi RNA gene.Northern blot analysis indicated that they were significantly downregulated in Pst DC3000-infected plants pretreated with AR156, in contrast to the plants without AR156 pretreatment. mi R825 targets two ubiquitin-protein ligases,while mi R825 targets toll-interleukin-like receptor(TIR)-nucleotide binding site(NBS) and leucine-rich repeat(LRR)type resistance(R) genes. The expression of these target genes negatively correlated with the expression of mi R825 and mi R825. Moreover, transgenic plants showing reduced expression of mi R825 and mi R825 displayed enhanced resistance to Pst DC3000 infection, whereas transgenic plants overexpressing mi R825 and mi R825 were more susceptible. Taken together, our data indicates that Bacillus cereus AR156 pretreatment primes ISR to Pst infection by suppressing mi R825 and mi R825 and activating the defense related genes they targeted.