Nitric oxide generated by Piriformospora indica-induced nitrate reductase promotes tobacco growth by regulating root architecture and ammonium and nitrate transporter gene expression

ABSTRACT 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 signal induced by P. indica is significantly different from that induced by the pathogen Phytophthora nicotianae. Inoculation with P. indica did not produce H2O2 and maintained high expression of Phytoglobin 1 in roots, resulting in a significantly lower NO level than in the roots inoculated with P. nicotianae. These findings suggest that an appropriate NO level is the likely basis of plant-P. indica symbiosis, which promotes the growth of host plants.