Abstract
We studied IAA5, IAA19, and DR5, a synthetic auxin responsive element (so called AuxRE), -GUS genes in response to exogenous indole-3-acetic acid (IAA) and brassinolide (BL). Exogenous IAA induced these genes quickly, transiently, and dose-dependently, while exogenous BL induced these genes gradually, continuously and dose-independently. Both IAA- and BL-induction kinetics were conserved not only between the two IAA genes but also between the IAA and DR5-GUS genes, suggesting that the IAA genes were induced by BL at least in part via the AuxRE activation. These genes were induced by BL in Arabidopsis seedlings without increase in endogenous IAA per fresh weight. Transcript abundance of IAA5 gene in det2 mutant were lower than in WT, suggesting that decreased BRs down-regulated IAA5 genes without decrease in IAA per fresh weight. In conclusion, transcriptional system consisting of AuxRE can be a crosstalk point for BR- and auxin-signaling pathway.
