Phosphate-solubilizing bacterium Burkholderia sp. strain N3 facilitates the regulation of gene expression and improves tomato seedling growth under cadmium stress

Abstract

Cadmium (Cd) is among the most toxic heavy metals in soils. The ways by which tomato plants inoculated with a phosphate-solubilizing bacterium (PSB) respond to Cd and regulate gene expression remain unclear. We investigated hormone metabolism and genes involved in Cd resistance in tomato seedlings inoculated with the PSB strain N3. Cd inhibited tomato plant growth and nutrient uptake and increase in dry weight. Compared with Cd treatment, N3 inoculation inhibited the accumulation of Cd in the shoots and roots, and the root dry weight significantly increased by 30.50% (P < 0.05). The nitrogen and potassium contents in the roots of seedlings treated with N3 increased, and the phosphorus levels were the same as those in the control. N3 decreased the rate of Zn2+ absorption but increased Fe3+ absorption in the roots, and the amount of accumulated Cd increased with Zn2+ uptake. The concentrations of hormones (indole-3-acetic acid, IAA; zeatin, ZEA; and jasmonic acid, JA) increased under Cd stress, whereas inoculation with N3 reduced IAA and ZEA levels. In the comparison between N3 + Cd and Cd treatments, the highest number of up- and downregulated genes was obtained. Pathways involved in signaling response, photosynthesis, phenylpropanoid biosynthesis, and DNA replication and the photosynthesis-antenna proteins pathway play important roles in the responses and adaptation of seedlings to Cd. Inoculation with N3 alleviates Cd stress in tomato seedlings. The present study provides new insights into the differentially expressed genes related to interaction between PSB and tomato exposed to Cd in soils.