Effects of phosphorus on the expression and regulatory path of nutrient transporter genes in tobacco

Objectives Phosphorus (P) has complex interactions with other mineral nutrients in plants. Here, we studied the effects of low and high P supply levels on the absorption and partition of mineral nutrients and nutrient transportation mechanism.

Methods Three P concentrations were setup in the culture solution-low (LP, 0.1 mmol/L), normal control (CK, 1 mmol/L), and high (HP, 5 mmol/L) using four weeks old tobacco seedlings (Nicotiana tabacum L. cv. K326) as test materials. On the sixth week of treatment, the plant samples were collected and divided into root, leaves and bud, for the determination of mineral nutrient contents. The isolation and quantitative expression assay of transporter genes (containing the cis-regulatory motif P1BS) in the root were carried out using RT-qPCR technique. The binding of K⁺ and Mg²⁺ transporter genes by NtPHR2 through P1BS cis-element was evaluated using molecular methods.

Results Both LP and HP inhibited tobacco growth and shoot biomass accumulation. Increasing P supply concentration enhanced the P, K and Mg concentrations in the root and shoot tissues of the crop. LP and HP treatment reduced the Ca concentration. The concentrations of Cu, Fe and Zn in the roots were not significantly affected by P supply, while LP significantly reduced the uptake of Mn and promoted the transfer to the shoot. We located 86 genes encoding transportation of mineral nutrients containing the cis-regulatory motif (P1BS). The relative expression of the selected 12 genes varied with HP and LP treatments. The LP and HP up-regulated the expressions of P, K, Ca, Mg, and Fe transporter genes, LP up-regulated and HP down-regulated the expressions of Cu transporter genes, and one Zn transporter gene down regulated and the other Zn transporter up regulated in LP and HP treatment. Meanwhile, we identified K⁺ and Mg²⁺ transporter genes directly regulated by NtPHR2 by binding to P1BS cis-element.

Conclusions Both low and high P supply inhibit tobacco growth and absorption and partitioning of mineral nutrients to some extent. From the molecular perspective, P stimulates the expression and transportation of K and Mg genes directly by binding to P1BS cis-element of K⁺ and Mg²⁺ transporter genes. The strong interactions between P and other mineral elements suggest that nutrient transport and P-signaling appear to mediate tobacco growth.