cAMP: the true second messenger in transcriptional auxin signaling

Auxins were the first of the major plant hormones and played key roles in plant growth and development. Auxin triggered gene expression through several mechanisms. The canonical textbook model is that auxin binds to TIR1/AFB receptors and stabilizes their interaction with Aux/IAA repressors, leading to their ubiquitination and degradation, which results in activation of ARFs transcription factors. The recent study published in Nature by Jiří Friml and co-authors updated the view on gene expression regulated by auxin. The role of TIR-produced cAMP was confirmed to be the second messenger in transcriptional auxin signaling. The conclusions raised in this Nature article shift the paradigm about the regulation of plant growth and development by auxin to the modulation of cAMP production and its interaction with candidate targets.