Promotion of plant growth by endophyte Bacillus amyloliquefaciens N3 through modulation of auxin translocation under nitrate-limited conditions

Numerous rhizobacteria have been isolated and could be utilized in an environmentally friendly way to improve crop yield by promoting plant growth. However, the underling mechanism is not well understood. In this study, we demonstrated that Bacillus amyloliquefaciens N3 isolated from purple soil promoted the lateral root formation and plant growth under nitrate-limited conditions. B. amyloliquefaciens N3 increased the local auxin accumulation in the lateral root tip, which may be attributed to the upregulated expression of PIN-FORMED ( PIN ) genes. Auxin polar transportation inhibition by NPA neutralized the promotion effects on lateral root density. Genetic analysis with mutants auxin response regulator 7 ( arf7 ), arf9 , and nitrated transporter 1.1 ( nrt1.1 ) revealed that the promotion of plant growth by B. amyloliquefaciens N3 depends on both auxin-responsive ARF-mediated transcriptional regulation and NRT1.1 under limited nitrate conditions. Stable promotion effects of B. amyloliquefaciens N3 on crop plants such as Brassica napus and Zea mays were validated in soil cultivation conditions. In summary, our study revealed further insights of the interaction mechanism between endophytic bacteria and plants and provided valuable resources for biofertilizer development.