Genome-wide Analysis of a Small Family of Atypical Non-DNA Binding Basic helix-loop-helix Transcription Factors in Auxin Responses in Arabidopsis

Auxins are a class of plant hormones that regulate multiple aspects of plant growth and development. In Arabidopsis, Paclobutrazol Resistance (PRE) transcription factors are a subfamily of atypical non-DNA binding basic helix-loop-helix (bHLH) proteins that have been shown to be involved in response to hormonal signals. Here, we provide molecular and genetic evidence that PRE proteins are involved in auxin signaling. We found that among a small family of PREs, the expression of PRE2, PRE5 and PRE6 can be induced by auxins. Transgenic plants overexpressing each of these three PRE genes displayed various auxin-related phenotype including elongated hypocotyl, elongated petiole and narrow leaves. Consistent with these observations, PRE2 and PRE6 overexpression lines displayed altered responses to auxin in the DR5:GUS reporter and auxin inhibition of root elongation assays. Collectively, these results demonstrate that some members of PRE proteins play regulatory roles in auxin responses.