Abstract
Cucumber seedlings grown in a horizontal position develop a peg on the lower side of transition zone between the root and the hypocotyl. We have shown that auxin induces peg formation and that following gravistimulation auxin and mRNA of auxin-responsible genes accumulate asymmetrically across the transition zone. We showed that CsARF2 and CsIAA1 mRNAs accumulate in the same tissue at the stage of peg initiation. We therefore proposed that CsARF2 may activate auxin-responsible genes responsible for peg formation and that co-expression of CsARF2 and CsIAAs is important for transcriptional regulation of the auxin response. In this study, we examined transcriptional activity of CsARFs and CsIAAs by tobacco BY-2 protoplast transient assay. We found that CsARF2 activated the transcription of auxin-responsible DR5 promoter in the assay. We discuss the mechanism of the transcriptional regulation of auxin responsible genes by CsARFs and CsIAAs, which may play a role in peg formation.
