Abstract
The early auxin-inducible genes, IAA3, 5, 19 and SAUR-AC1 as well as a synthetic auxin-response element, DR5, were induced quickly in response to brassinosteroid (BR) treatment. Either of BR- and auxin-induction kinetics was similar between the early auxin-inducible genes and the DR5. We identified BR and auxin-inducible genes comprehensively using GeneChip. The frequencies of the auxin-response element, TGTCTC, was not enriched in auxin-specific genes, but was enriched in genes regulated by both BR and auxin. AXR1 , an homolog of the ubiquitin-activating enzyme E1, functions as an positive regulator of auxin-signaling. The axr1 mutant was insensitive to BR-induced hypocotyl elongation and SAUR-AC1 gene expression. YkB, an inhibitor of auxin action, inhibited BR-induced gene expression, whereas PCIB, an antagonist of auxin, did not inhibited BR-induced gene expression. The results suggested that the signaling pathway of BR interacts with that of auxin at upstream of ubiquitin-proteasome-mediated protein degradation system.
