Reducing phenanthrene uptake and translocation, and accumulation in the seeds by overexpressing OsNRT2.3b in rice

Abstract

The uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in crops have gained much attention due to their toxicity to humans. Nitrogen (N) is an essential element for plant growth and has also been implicated in the acquisition and acropetal translocation of PAHs. OsNRT2.3b encodes a nitrate (NO3−) transporter that is involved in the acquisition and mobilization of N in rice. Here, we investigated whether overexpression of OsNRT2.3b would exert any mitigating influence on the uptake and translocation of phenanthrene (Phe, a model PAH) in transgenic rice (Oryza sativa). The wild-type seedlings exhibited a reduction in plant height, primary root length, and shoot biomass when grown hydroponically in a medium supplemented with Phe. Acquisition of Phe by the roots and its subsequent translocation to shoots increased concomitantly with an increase in Phe concentration in the medium and duration of the treatment. OsNRT2.3b-overexpressing lines (Ox-6 and Ox-8) were generated independently. Compared with the wild-type, the concentration of Phe in Ox-6 and Ox-8 were significantly lower in the roots (47%–54%) and shoots (22%–31%) grown hydroponically with Phe (1 mg/L). Further, the wild-type and Ox lines were grown to maturity in a pot soil under Phe conditions and the concentrations of Phe and total N were assayed in the culms and flag leaves. Compared with the wild-type, in Ox lines the concentration of total N significantly increased in the culms (288%–366%) and flag leaves (12%–25%), while that of Phe significantly reduced in the culms (25%–28%) and flag leaves (18%–21%). The results revealed an antagonistic correlation between the concentration of total N and Phe. The concentration of Phe was also significantly lower (29%–38%) in the seeds of Ox lines than the wild-type. The study highlighted the efficacy of overexpressing OsNRT2.3b in mitigating the Phe toxicity by attenuating its acquisition, mobilization, and allocation to the seeds.