Redox regulation of SCFTIR1 E3 ligase complex involved in auxin signaling by S-nitrosylation in Arabidopsis plants.

IGLESIAS MJ; TERRILE MC; CASALONGUÉ, CA

Congreso; EMBO-CONICET Conference: ?Ubiquitin & ubiquitin-like proteins: At the crossroads from chromatin to protein; 2014

The ubiquitin-proteasome system (UPS) plays a role in nearly every aspect of plant biology. UPSaction appears to regulate hormone biosynthesis, transport and perception and thus provides a directmechanism to control the magnitude and duration of hormone signalings in plants. The SCFcomplex is one of the most important E3 ligases in Arabidopsis and is composed of four primarysubunits: Cullin1, Skp1/ASK1, Rbx1 and an F-box protein. In general, a long-standing objective ofthe study of plant hormone action has been to elucidate the molecular basis of signaling systemsthat are operating to transduce hormone messages into the physiological responses that theyregulate.The plant hormone auxin has been implicated in almost every stage of plant growth anddevelopment from embryogenesis to senescence. Auxin interacts directly with the F-box protein,TIR1, of E3 ligase complex SCFTIR1 and promotes the interaction with a family of transcriptionalrepressors called Aux/IAA proteins facilitating their rapid degradation via 26S proteasome.We have provided evidence for nitric oxide (NO)-mediated modulation of auxin signaling throughS-nitrosylation of the TIR1 auxin receptor which is an F-box protein of the SCF complex. The firstevidence of a plant E3 ligase acting as hormonal receptor and modified by S-nitrosylation wasdemonstrated in our laboratory. S-nitrosylation of TIR1 modulates TIR1-Aux/IAA protein-proteininteraction resulting in activation of auxin signaling. Our ultimate goal is to understand NOmediatedredox regulation of the different subunits of the SCFTIR1 complex. Thus, wehypothesized that dynamic events of S-nitrosylation could modulate the assembly ofSCFTIR1/AFBs complex due to stabilization of different combinatorial protein-protein interactions.Redox regulation of the different subunits of the complex could have major functional implicationsbecause different F-box proteins can be associated interchangeably with ASK1 to form a largenumber of different SCF complexes with different substrate specificities and functions in plantdevelopment. Furthermore, the universality of both, S-nitrosylation and degradation via UPS systemprovide a valuable platform to go forward and deep into the conservatory basis of redox-regulatedUPS complexes in eukaryotes.