Plants mainly uptake inorganic nitrogen from soil as ammonium and nitrate. Less energy is required to assimilate ammonium compared to nitrates, and plants prefer to take up ammonium when the external nitrogen concentration is low. Investigating the patterns and mechanisms of ammonium absorption can help improve crop nitrogen utilization. In this study, we isolated MdSAT1, a gene of apple encoding an ammonium-responsive bHLH transcription factor. MdSAT1 promoted the growth and development of lateral roots and root hairs. Overexpression of MdSAT1 increased the transcript levels of genes related to ammonium uptake, indicating that MdSAT1 can regulate ammonium uptake and utilization at the transcriptional level. MdSAT1 also can modulate reactive oxygen species (ROS) accumulation to ultimately regulate plant growth. Taken together, these findings provide insight for us to further study the mechanisms by which MdSAT1 controls ammonium utilization as well as plant growth and development.
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