The H167 Site in OsNRT2.3b Reduces Phenanthrene Accumulation in Rice under Combined Acidity and Nitrogen Deficiency

Minimizing the accumulation of polycyclic aromatic hydrocarbons (PAHs) in crops is crucial for human health. While OsNRT2.3b overexpression reduced phenanthrene (Phe) in rice, the underlying mechanisms and its response to complex conditions remained unclear. This study first confirmed a negative correlation between OsNRT2.3b expression and Phe utilizing 16 varieties. Further, to investigate whether the pH-sensing site H167 of OsNRT2.3b is the key, the wild-type (WT), OsNRT2.3b-overexpression (Ox), and H167-mutated OsNRT2.3b overexpression (H167R) were employed to expose to Phe under different nitrogen (N) and pH. Individual N and pH experiments demonstrated that H167 played a decisive role in suppressing Phe, with Phe in H167R being significantly higher than Ox. Moreover, both -N compared to + N, and pH 4.0 compared to 7.0, increased Phe while simultaneously enhancing H167-mediated regulation. Phe in Ox was significantly lower than H167R by 24.6% (-N) and 22.3% (pH 4.0). Combined pH and N treatments revealed that H167 was most effective under acidic and N-deficient conditions. Under hydroponic pH 4.0 & -N and pot soil pH 5.4 & LN, Phe in the roots of Ox were 19.7% and 17.3% lower than H167R. Effect size analysis indicated that an acidic environment exerted a stronger effect on H167-mediated Phe reduction than N under the conditions tested. Notably, in grains, the pH-specific mediation by H167 decreased Phe by 16.6% under acidic and N-deficient soil. This study provides a basis for mitigating Phe accumulation and associated PAH-related risks in rice through molecular strategies and soil pH and N management.