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Combining phytoremediation plants and microorganisms is a promising method of remediating heavy metal contaminated soil. In this study, two manganese-tolerant strains were isolated from Mn slag and identified as Bacillus cereus HM5 and Bacillus thuringiensis HM7. These two Bacillus spp. have the ability to dissolve phosphorus, produce IAA and iron carrier. A pot experiment of Broussonetia papyrifera was conducted to explore potential of B. cereus HM5 and B. thuringiensis HM7 to improve effect of remedying Mn pollution by B. papyrifera. The strains were inoculated under different Mn treated (5 mmol/L, 50 mmol/L, Mn slag) respectively and the growth, root structure, root activity, physiological and biochemical characteristics of the leaves and accumulation of Mn for B. papyrifera were determinated. The effects of the soil environment to remediation were observed, the results showed that the biomass, total root length, surface area, crossings, tips, forks and root activity of B. papyrifera with inoculated strain were higher than those of the control group. The inoculation of these two Bacillus spp. increased the absorption of Mn by B. papyrifera and the concentration of Mn in the aerial parts of plants, indicating that the two strains could promote the growth of B. papyrifera and the accumulation of Mn. In addition, microbes reduced malonaldehyde content and the activities of antioxidant enzymes in leaves, suggesting that the two Bacillus spp. reduced Mn-induced oxidative stress. The principal component analysis showed that the added Bacillus strain prefer to promote plant root function maintenance and improve soil environment, rather than direct adsorption of heavy metals. These observations indicated that B. cereus HM5 and B. thuringiensis HM7 were valuable microorganisms, which could improve the remediating efficiency of B. papyrifera under Mn-contaminated soil. • B. cereus HM5/ B. thuringiensis HM7 improved the accumulation of Mn by B. papyrifera. • B. cereus HM5 and B. thuringiensis HM7 could reduce oxidative stress induced by Mn. • The strains promoted the growth of plant root system and improved soil environment. [ABSTRACT FROM AUTHOR]

Heavy metal pollution has become increasingly prominent, and bioremediation of heavy metal polluted areas is urgently needed. Broussonetia papyrifera is a pioneer tree species for vegetation restoration in the tailings area, while its molecular mechanism of heavy metal adaptation is not clear. Here, we report that a R2R3 MYB from B. papyrifera (BpMYB1) is involved in Cd accumulation by controlling the down-stream genes and mineral accumulation. Overexpression of BpMYB1 in B. papyrifera resulted in a significant increase in Cd accumulation and multiple gene transcription. Among the up-regulated genes, BpMYB1 could bind to ferrochelatase (BpFC2), basic helix-loop-helix transcription factor bHLH93 (BpbHLH93), and basic leucine zipper transcription factor bZIPs (BpbZIP1 , BpbZIP-CPC1) by recognizing TATCCAOSAMY (TATCCA) motif and related promoter segments. Further investigations revealed that overexpression of BpbZIP1 promotes the absorption of Cd, BpMYB1 regulate Cd uptake in plant relating to Fe accumulation without Fe-deficiency pathway via recognizing the downstream BpbHLH93 and involving in PCs biosynthetic pathway via recognizing the target BpFC2. Moreover, the Cd response effect mediated by BpMYB1 was boosted by interacting with a DELLA protein BpGAI1, a vital member of GA signaling. These results provide new insights into the molecular feedback mechanisms underlying BpMYB1-BpGAI1 controlled Cd uptake in plants, which will benefit for phytoremediation of Cd polluted soil. [Display omitted] • BpMYB1 overexpression benefits for Cd enrichment and tolerance of B. papyrifera. • BpMYB1 could regulate the transcription of multiple genes in Cd stress response. • The Cd stress response of BpMYB1 involves in the gibberellin-dependant signaling. • BpMYB1 could recognize downstream genes of BpFC2 , BpbHLH93 , BpbZIP1 , BpbZIP-CPC1. • BpFC2 , BpbHLH93 , BpbZIP1 , BpbZIP-CPC1 overexpression improves plant Cd uptake. [ABSTRACT FROM AUTHOR]