WRKY46 promotes ammonium tolerance in Arabidopsis by repressing NUDX9 and IAA-conjugating genes and by inhibiting NH4 + efflux in the root elongation zone.

Ammonium (NH4 + ) is toxic to root growth in most plants already at moderate levels. Transcriptional regulation is one of the most important mechanisms in plant's response to NH4 + toxicity, but the nature of the involvement of transcription factors (TFs) in this regulation remains unclear. Here, RNA-seq analysis in Arabidopsis roots was performed to screen ammonium-responsive TFs. WRKY46, the member of the WRKY transcription factor family most responsive to NH4 + , was selected. We define the role of WRKY46 by using mutation and overexpression assays, and characterize the regulation of NUDX9 and IAA-conjugating genes by WRKY46 via yeast one-hybrid and electrophoretic mobility shift assays and ChIP-quantitative PCR. Knockout of WRKY46 increased, while overexpression of WRKY46 decreased, NH4 + -suppression of the primary root. WRKY46 is shown to directly bind to the promoters of the NUDX9 and IAA-conjugating genes (GH3.1, GH3.6, UGT75D1, UGT84B2) and inhibits their transcription, thus positively regulating free IAA content and stabilizing protein N-glycosylation, leading to an inhibition of NH4 + efflux in the root elongation zone (EZ). We identify TF involvement in regulating NH4 + efflux in the EZ, and show that WRKY46 inhibits NH4 + efflux by negative regulation of NUDX9 and IAA-conjugating genes. This article is protected by copyright. All rights reserved.