NtARF11 positively regulates cadmium tolerance in tobacco by inhibiting expression of the nitrate transporter NtNRT1.1

Heavy metal cadmium (Cd) is widespread in contaminated soil and an important factor limiting plant growth. NO3- (nitrate) affects Cd uptake and thus changes Cd tolerance in plants; however, the underlying molecular regulatory mechanisms have not yet been elucidated. Here, we analyzed a novel gene, NtARF11 (auxin response factor), which regulates Cd tolerance in tobacco via the NO3- uptake pathway, through experiments with NtARF11-knockout and NtARF11-overexpression transgenic tobacco lines. NtARF11 was highly expressed under Cd stress in tobacco plants. Under Cd stress, overexpression of NtARF11 enhanced Cd tolerance in tobacco compared to that in wild-type tobacco, as shown by the low Cd concentration, high chlorophyll concentration, and low accumulation of reactive oxygen species in NtARF11-overexpressing tobacco. Moreover, low NO3- concentrations were observed in NtARF11-overexpressing tobacco plants. Further analyses revealed direct binding of NtARF11 to the promoter of the nitrate transporter NtNRT1.1, thereby negatively regulating its expression in tobacco. Notably, NtNRT1.1 knockout reduced NO3- uptake, which resulted in low Cd concentrations in tobacco. Altogether, these results demonstrate that the NtARF11-NtNRT1.1 module functions as a positive regulator of Cd tolerance by reducing the Cd uptake in tobacco, providing new insights for improving Cd tolerance of plants through genetic engineering.