osa-miR528 promotes seedling growth by enhancing nitrate uptake under nitrogen deficiency in rice

Nitrogen (N) is required for a plant’s normal growth and development. It has been shown that miRNAs play a vital role in N uptake, assimilation and translocation in plants. However, there are few studies, so far, showing a single miRNA regulating seedling growth under varying N concentrations from different sources. Here, we showed that the expression of rice miR528 was higher when induced by NO3--N than that by NH4+-N. Further analysis indicated that overexpression of miR528 (OE) increased seedling biomass and roots total N content up to 82.70% and 133.31%, respectively, under NO3--N deficiency. Conversely, mir528 exhibited an opposite phenotype compared with the OE plants, that is, a large margin of decrease of seedling biomass and roots’ total N content up to 21.60% and 22.45%, respectively. In addition, short-term 15NO3- influx rates and mean net NO3- influx rates were increased in OE plants, which was consistent with the upregulated expression of OsNRT2s family member genes under NO3--N deficiency condition. What’s more, OsAO was identified as the downstream target in response to NO3--N and reduced AO activity in OE plants was found under NO3--N starvation. Our data established that miR528 plays a positive role in regulating rice seedling growth in response to N deficiency, illustrating its capacity for engineering biomass improvement in crops.