Endophytic Bacillus sp. AP10 harboured in Arabis paniculata mediates plant growth promotion and manganese detoxification

Phytoremediation of heavy metal-polluted soils assisted by plant-associated endophytes, is a suitable method for plant growth and manganese (Mn) removal in contaminated soils. This investigation was conducted to evaluate the Mn-resistant endophytic resources of the Mn hyperaccumulator Arabis paniculata and their functions in the phytoremediation of Mn2+ toxicity. This study isolated an endophytic bacterium with high Mn resistance and indole-3-acetic acid (IAA) production form A. paniculata and identified it as Bacillus sp. AP10 using 16 S rRNA gene sequencing analysis. The effects of Bacillus sp. AP10 on the alleviation of Mn2+ toxicity in Arabidopsis thaliana seedlings and the molecular mechanisms were further investigated using biochemical tests and RNA-seq analysis. Under Mn2+ stress, Bacillus sp. AP10 increased the biomass, chlorophyll content and the translocation factor (TF) values of Mn in the aerial parts, while decreased the malondialdehyde (MDA) content of A. thaliana seedlings compared with that of control plants. The differentially expressed genes (DEGs) and enrichment analysis showed that Bacillus sp. AP10 could significantly increase the expression of key genes involved in cell-wall loosening, which may improve plant growth under Mn stress. Superoxide dismutase (SOD)-encoding genes were detected as DEGs after AP10 treatment. Moreover, AP10 regulated the expression of genes responsible for phenylpropanoid pathway, which may promote antioxidant flavonoids accumulation for reactive oxygen species (ROS) scavenging to improve Mn tolerance. The activation of ATP-binding cassette (ABC) transporter gene expression especially ABCB1 after AP10 stimulation, explained the elevation of metal ion binding or transport related to enhanced Mn accumulation in plants. Futhermore, AP10 might alleviate Mn toxicity through enhancing abscisic acid (ABA) responsive gene expression and ABA biosynthesis. These findings provide new insights into the functions and regulatory mechanism of Bacillus sp. AP10 in promoting plant growth, and tolerance, improving Mn accumulation and alleviating Mn2+ toxicity in plants. The application of Bacillus sp. AP10 as potential phytoremediators may be a promising strategy in Mn2+ contaminated fields. Availability of data and materials: The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.