Les séminaires ont lieu sur le Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)
Jeudi 19 mai 2011
Amphi 208 (Cœur d’Ecole) à 14h
The auxin receptor ABP1 is modulating the TIR1/AFB-Aux/IAA auxin signalling pathway
Institut des Sciences Végétales-CNRS-Gif sur Yvette
Auxin is a major plant hormone that controls most aspects of plant growth and development. Auxin is perceived by two distinct classes of receptors. The first class corresponds to nuclear auxin co-receptors resulting from the interaction of Transport Inhibitor Response 1 (TIR1) or related Auxin-signaling F-Box (AFBs) F-box proteins with Aux/IAA transcriptional repressors . The other is the Auxin Binding Protein 1 (ABP1) that perceives extracellular auxin, activates a transduction cascade at the plasma membrane, and was recently shown to be involved in a wide variety of auxin-dependent responses including regulation of clathrin-dependent endocytosis , activation of rho-GTPases and modulation of gene expression . The mode of action of ABP1 in the fine tuning of auxin-regulated transcription is however not understood. Here, we show that reducing the function of ABP1 leads to an increased degradation of Aux/IAA protein reporter in plant roots via the SCFTIR1/AFB ubiquitine ligase pathway. We also found that multiple tir1,afb null mutations are epistatics on ABP1 inactivation, thus placing ABP1 genetically upstream of TIR1/AFB. Our results demonstrate that an exaggerated degradation of Aux/IAA repressors is deleterious for root growth and development and that regulation of their half-life requires a negative regulation of the SCFTIR1/AFB signaling pathway. This negative regulation is mediated by an ABP1-dependent signalling cascade that counterbalances promotion of Aux/IAA degradation. We propose that such dual control of protein turn-over is essential to control the homeostasis of Aux/IAA repressors that defines the threshold and the time scale of cell responsiveness to auxin. Control of protein turn-over is central for various plant hormone signalling pathways and combining positive and negative regulations of SCF ubiquitin-proteasome pathways might be a common trait conferring a tight control of hormone-mediated responses.
Contact : Catherine Curie