Brassinosteroid transcription factor BES1 modulates nitrate deficiency by promoting NRT2.1 and NRT2.2 transcription in Arabidopsis.

SUMMARY: Nitrogen (N) is one of the most essential mineral elements for plants. Brassinosteroids (BRs) play key roles in plant growth and development. Emerging evidence indicates that BRs participate in the responses to nitrate deficiency. However, the precise molecular mechanism underlying the BR signaling pathway in regulating nitrate deficiency remains largely unknown. The transcription factor BES1 regulates the expression of many genes in response to BRs. Root length, nitrate uptake and N concentration of bes1‐D mutants were higher than those of wild‐type under nitrate deficiency. BES1 levels strongly increased under low nitrate conditions, especially in the non‐phosphorylated (active) form. Furthermore, BES1 directly bound to the promoters of NRT2.1 and NRT2.2 to promote their expression under nitrate deficiency. Taken together, BES1 is a key mediator that links BR signaling under nitrate deficiency by modulating high affinity nitrate transporters in plants. Significance Statement: The accumulation of BES1 in the non‐phosphorylated state under low nitrogen conditions directly promotes their transcription by binding to the promoters of NRT2.1 and NRT2.2, thereby enhancing the uptake of NO3− in roots and improving the utilization efficiency of plants to nitrogen. The present study provides direct evidence that brassinosteroid signals are directly involved in the regulation of nitrogen uptake and nitrogen transporters. [ABSTRACT FROM AUTHOR]