Yuanhu Xuan
Shenyang Agricultural University,China
Title: RAV-Like 1 (RAVL1) regulates brassinosteroid-mediated activation of AMT1;2 in ric
Biography
Biography: Yuanhu Xuan
Abstract
The promotive action of brassinosteroids (BRs) on plant growth and development has been widely investigated at the genetic and cell biological level. Although growth promotion may also rely on improved plant nutrition, it is not known whether BRs may directly act on nutrient uptake. In this study, we explored the possibility of a direct relationship between BRs and ammonium uptake via expression of AMMONIUM TRANSPORTER 1 (AMT1)-type genes in rice roots. BR treatment increased the expression of AMT1;1 and AMT1;2, whereas in the mutant d61-1, which is defective in the BR-receptor gene BRI1, BR-dependent expression of these genes was suppressed. We then employed the transcription factor RAV-Like 1 (RAVL1), which is involved in BR homeostasis, to investigate BR-mediated AMT1 expression and its effect on NH4+ uptake in rice roots. BR-dependent induction of AMT1;2 was suppressed in the ravl1 mutant, while overexpression of RAVL1 increased AMT1;2 transcript levels. EMSA and ChIP analyses showed that RAVL1 activates the expression of AMT1;2 by directly binding to E-box motifs in its promoter. Moreover, 15NH4+ uptake in roots, cellular ammonium contents, and root responses to methyl ammonium strongly depended on RAVL1 expression levels. Analyzing AMT1;2 expression levels in different crossings between BRI1 and RAVL1 mutant and overexpression lines further indicated that RAVL1 acts downstream of BRI1 in the NH4+-dependent induction of AMT1;2. Thus, the present study shows how BRs can interfere with the transcriptional regulation of nutrient transporters to modulate their uptake capacity.