Involvement of the miR156/SPLs/NLP7 modules in plant lateral root development and nitrogen uptake.

Main conclusion: This study unravels a molecular mechanism of miR156/SPL module in regulating lateral root development and nitrogen uptake in apple. Nitrogen is critical in controlling lateral root development such as the availability or lack of nitrogen nutrients which can affect lateral root formation. The miR156/SPL module plays a pivotal role in regulating many aspects of plant development, including the timing of vegetative phase change, floral induction, shoot branching and root development. However, whether the miR156/SPL module functions in nitrate-mediated apple lateral root development remains largely unknown. Here, we revealed the role of miR156/SPL module in regulating lateral root development and root nitrogen uptake in both apple and Arabidopsis. This finding showed that miR156-targeted transcription factor MdSPL23 not only regulates lateral root development but also root nitrogen uptake. The MdSPL23 is bound to the promoter of MdNLP7 to suppress its expression, thereby negatively regulating nitrogen uptake and inhibiting lateral root development in apple. In a likewise manner, the AtSPL9 involved in lateral root development in Arabidopsis is bound to the MdNLP7 homologous gene AtNLP7 to suppress its expression to regulate nitrate-mediated lateral root development. These results suggest that plants regulate nitrogen-mediated root growth through miR156/SPL modules, and this mechanism might be of universal importance.