Abstract
Although it is known that brassinosteroids (BRs) play pleiotropic roles in plant growth and development, their roles in plant nutrient uptake remain unknown. Here, we hypothesized that BRs directly regulate ammonium uptake by activating the expression of rice AMT1-type genes. Exogenous BR treatment upregulated both AMT1;1 and AMT1;2 expression, while this induction was impaired in the BR-receptor gene BRI1 mutant d61-1. We then focused on brassinazole-resistant 1 (BZR1), a central hub of the BR signaling pathway, demonstrating the important role of this signaling pathway in regulating AMT1 expression and rice roots NH4+ uptake. The results showed that BR-induced expression of AMT1;2 was suppressed in BZR1 RNAi plants but was increased in bzr1-D, a gain-of-function BZR1 mutant. Further EMSA and ChIP analyses showed that BZR1 bound directly to the BRRE motif located in the promoter region of AMT1;2. Moreover, cellular ammonium contents, 15NH4+ uptake, and the regulatory effect of methyl-ammonium on root growth are strongly dependent on the levels of BZR1. Overexpression lines of BRI1 and BZR1 and Genetic combination of them mutants showed that BZR1 activates AMT1;2 expression downstream of BRI1. In conclusion, the findings suggest that BRs regulation of NH4+ uptake in rice involves transcription regulation of ammonium transporters.
Highlights
Inorganic nitrogen (N) is an important plant nutrient and is absorbed from the rhizosphere in two forms, nitrate and ammonium
To investigate whether BR affects the expression of rice AMT1, we used a series of BL concentration gradients of 0, 10, 100, and 200 nm to treat the wild-type, a weak allele of rice Brassinosteroid Insensitive 1 (BRI1) mutant, d61-1, and the BRI1 overexpression line bri1-D (Jeong et al, 2002), and compared the changes in the AMT1 expression level under the different treatment conditions
We identified two cis-elements targeted by the promoter of brassinazole-resistant 1 (BZR1) which are closely related to transcriptional activation of AMT1;2
Summary
Inorganic nitrogen (N) is an important plant nutrient and is absorbed from the rhizosphere in two forms, nitrate and ammonium. High levels of NH4+ are of particular importance to the rice yield. Further understanding of the molecular basis and regulation of ammonium transport and its translocation to buds is needed to promote efficient nitrogen absorption and to improve crop yields. Ammonium transporter (AMT) proteins can induce high-affinity NH4+ uptake from the rhizosphere to root cells, and the transporter AMT2;1 has been shown to play a crucial role in ammonium root-to-stem translocation (Giehl et al, 2017).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
