Nitric oxide (NO) is involved not only in the regulation of plant growth, development, and stress responses but also in the regulation of plant-microbe interactions. Here, we demonstrate that Piriformospora indica can induce tobacco nitrate reductase to produce a NO signal in roots which enhances nitrogen uptake capacity by inducing the expression of ammonium and nitrate transporter genes and the development of lateral root and root hair, thereby promoting tobacco growth. In addition, the NO...