AUTHOR=Yang Shuo , Yuan Depeng , Zhang Yang , Sun Qian , Xuan Yuan Hu 

TITLE=BZR1 Regulates Brassinosteroid-Mediated Activation of AMT1;2 in Rice

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.665883

DOI=10.3389/fpls.2021.665883

ISSN=1664-462X

ABSTRACT=<p>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 <italic>AMT1</italic>-type genes. Exogenous BR treatment upregulated both <italic>AMT1;1</italic> and <italic>AMT1;2</italic> expression, while this induction was impaired in the BR-receptor gene <italic>BRI1</italic> mutant <italic>d61-1</italic>. We then focused on brassinazole-resistant 1 (<italic>BZR1</italic>), a central hub of the BR signaling pathway, demonstrating the important role of this signaling pathway in regulating <italic>AMT1</italic> expression and rice roots NH<sub>4</sub><sup>+</sup> uptake. The results showed that BR-induced expression of <italic>AMT1;2</italic> was suppressed in <italic>BZR1 RNAi</italic> plants but was increased in <italic>bzr1-D</italic>, a gain-of-function <italic>BZR1</italic> mutant. Further EMSA and ChIP analyses showed that BZR1 bound directly to the BRRE motif located in the promoter region of <italic>AMT1;2</italic>. Moreover, cellular ammonium contents, <sup>15</sup>NH<sub>4</sub><sup>+</sup> uptake, and the regulatory effect of methyl-ammonium on root growth are strongly dependent on the levels of <italic>BZR1</italic>. Overexpression lines of <italic>BRI1</italic> and <italic>BZR1</italic> and Genetic combination of them mutants showed that BZR1 activates <italic>AMT1;2</italic> expression downstream of BRI1. In conclusion, the findings suggest that BRs regulation of NH4<sup>+</sup> uptake in rice involves transcription regulation of ammonium transporters.</p>