Resumen de la plática
The plant hormone auxin is a versatile endogenous signal influencing virtually all aspects of plant life. It has a unique ability to be directionally transported through tissues, forming local auxin maxima and gradients that are central to many developmental processes mediated by auxin. One of the key roles of auxin is the adaptation of plant growth to gravity, where shoots bend up and roots bend down. This paradox is based on the opposite responses of these organs to the phytohormone auxin, which promotes cell expansion in shoots through a canonical mechanism while rapidly inhibiting it in roots via a yet unknown, non-transcriptional downstream mechanism.
Nuclear, transcriptional auxin signalling involves the TIR1/AFB auxin receptors, Aux/IAA transcriptional repressors, and ARF transcription factors. TIR1/AFBs are part of the ubiquitin ligase complex, mediating the ubiquitination and degradation of Aux/IAAs and thereby releasing ARFs from their inhibition. The unexpected identification of adenylate cyclase enzymatic activity in TIR1/AFB receptors (Qi et al., 2022) and the crucial importance of its product, cAMP, for the downstream regulation of transcription (Chen et al., 2025) revise this canonical model, which has withstood the test of time for 20 years.
Nonetheless, auxin also triggers cellular responses within seconds—too fast to rely on transcription. The classical rapid auxin responses leading to root growth inhibition are mediated by the non-transcriptional branch of TIR1/AFB signalling, mainly through AFB1. The downstream mechanism is still unclear but may involve guanylate cyclase activity of TIR1/AFBs targeting calcium channels.
I will present these and other mechanistic updates on transcriptional and non-transcriptional auxin signalling and show how these insights may serve as a blueprint for gaining a new understanding of other signalling pathways in plants.

Jiří Friml. Institute of Science and Technology, Austria

http://ist.ac.at/research/research-groups/friml-group/

Frontiers in Genomics