Enterobacter asburiae Reduces Cadmium Toxicity in Maize Plants by Repressing Iron Uptake-Associated Pathways

Soil
microbes have recently been utilized
to improve cadmium (Cd) tolerance and lower its accumulation in plants.
Nevertheless, whether rhizobacteria can prevent Cd uptake by graminaceous
plants and the underlying mechanisms remain elusive. In this study,
inoculation with Enterobacter asburiae NC16 reduced transpiration rates and the expression of some iron
(Fe) uptake-related genes including ZmFer, ZmYS1, ZmZIP, and ZmNAS2 in maize (Zea mays) plants, which
contributed to mitigation of Cd toxicity. However, the inoculation
with NC16 failed to suppress the transpiration rates and transcription
of these Fe uptake-related genes in plants treated with fluridone,
an abscisic acid (ABA) biosynthetic inhibitor, indicating that the
impacts of NC16-inoculation observed were dependent on the actions
of ABA. We found that NC16 increased the host ABA levels by mediating
the metabolism of ABA rather than its synthesis. Moreover, the capacity
of NC16 to inhibit plant uptake of Cd was greatly weakened in plants
overexpressing ZmZIP, encoding a zinc/iron transporter.
Collectively, our findings indicated that E. asburiae NC16 reduced Cd toxicity in maize plants at least partially by hampering
the Fe uptake-associated pathways.