Over recent decades, the application of N fertilizers has increased food production and decreased hunger globally ( Good et al., 2004 Ju et al., 2009). Nitrogen (N) is a major macronutrient for plant growth and crop yield. These data contribute to a molecular approach to improve the N usage of fruit crops under limited N acquisition. The results obtained illustrate the mechanism of a regulatory module comprising MdBT2–MdMYB88/MdMYB124–MdNRTs, through which plants modulate N usage.
In contrast, MdMYB88 and MdMYB124 increase nitrate absorption, allocation, and remobilization by regulating expression of MdNRT2.4, MdNRT1.8, MdNRT1.7, and MdNRT1.5 under N limitation, thereby regulating N usage. MdBT2 negatively regulates nitrogen usage as revealed by the reduced fresh weight, dry weight, N concentration, and N usage index of MdBT2 overexpression calli under low-N conditions.
Ubiquitination and protein stabilization analysis revealed that MdBT2 ubiquitinates and degrades MdMYB88 and MdMYB124 via the 26S proteasome pathway. By conducting yeast two-hybrid assays, we identified one interacting protein of MdMYB88 and MdMYB124 in apple ( Malus × domestica), namely BTB and TAZ domain protein 2 (MdBT2). However, the underlying regulation of these processes remains largely unknown, particularly in woody plants. Thus, improving the N use efficiency of crops is critical for agricultural development.
Less than 40% of the nitrogen (N) fertilizer applied to soil is absorbed by crops.
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