Polyamine-producing bacterium Bacillus megaterium N3 reduced Cd accumulation in wheat and increased the expression of DNA repair- and plant hormone- related proteins in wheat roots

Abstract Metal-immobilizing bacteria play an important role in reducing the metal uptake of plants. However, little research has characterized the effects of polyamine-producing bacteria on the inhibition of Cd uptake in wheat. Herein, the effects of Bacillus megaterium N3 on wheat Cd uptake and the differentially expressed proteins in wheat roots were studied using hydroponic experiments. The results showed that under 3 mg L-1 Cd stress, strain N3 reduced the Cd content in wheat roots (33.59%) and leaves (82.83%) compared with no inoculation. Strain N3 significantly reduced (24.19%-31.02%) the proportion of Cd in the organelles and the soluble fraction and increased (74.91%) the proportion of Cd in the cell walls of wheat roots. Moreover, the contents of abscisic acid and polyamines in the wheat roots and leaves also increased (22.64%-372.8%) in the presence of strain N3 under 3 mg L-1 Cd. Label-free proteomics showed that 127 and 85 proteins were up- and downregulated in the N3+Cd treatment compared with the Cd treatment. The significantly enriched items were identified as a protein-DNA complex, DNA packaging complex, intercellular transport, peroxidase activity, and transferase activity. Moreover, the expression of DNA replication, plant hormone, and Fe-Zn transporter related proteins in wheat roots was increased in the presence of strain N3 compared with uninoculated roots under Cd stress. These results provide new insights and a theoretical basis for applying polyamine-producing bacteria to safe wheat production.