TY - INPR ID - 2481 TI - Flexibility of intrinsically disordered degrons in AUX/IAA proteins reinforces auxin receptor assemblies JO - bioRxiv PY - 2019 SP - AU - Niemeyer, M. AU - Moreno Castillo, E. AU - Ihling, C. H. AU - Iacobucci, C. AU - Wilde, V. AU - Hellmuth, A. AU - Hoehenwarter, W. AU - Samodelov, S. L. AU - Zurbriggen, M. D. AU - Kastritis, P. L. AU - Sinz, A. AU - Calderón Villalobos, L. I. A. VL - UR - https://dx.doi.org/10.1101/787770 DO - 10.1101/787770 AB - Cullin RING-type E3 ubiquitin ligases SCFTIR1/AFB1-5 and their ubiquitylation targets, AUX/IAAs, sense auxin concentrations in the nucleus. TIR1 binds a surface-exposed degron in AUX/IAAs promoting their ubiquitylation and rapid auxin-regulated proteasomal degradation. Here, we resolved TIR1·auxin·IAA7 and TIR1·auxin·IAA12 complex topology, and show that flexible intrinsically disordered regions (IDRs) in the degron′s vicinity, cooperatively position AUX/IAAs on TIR1. The AUX/IAA PB1 interaction domain also assists in non-native contacts, affecting AUX/IAA dynamic interaction states. Our results establish a role for IDRs in modulating auxin receptor assemblies. By securing AUX/IAAs on two opposite surfaces of TIR1, IDR diversity supports locally tailored positioning for targeted ubiquitylation and might provide conformational flexibility for adopting a multiplicity of functional states. We postulate IDRs in distinct members of the AUX/IAA family to be an adaptive signature for protein interaction and initiation region for proteasome recruitment. KW - Proteomics A2 - C1 - Synergy Research Groups; Molecular Signal Processing ER - TY - JOUR ID - 2091 TI - Variation in auxin sensing guides AUX/IAA transcriptional repressor ubiquitylation and destruction. JO - Nature Commun. PY - 2017 SP - 15706 AU - Winkler, M. AU - Niemeyer, M. AU - Hellmuth, A. AU - Janitza, P. AU - Christ, G. AU - Samodelov, S. L. AU - Wilde, V. AU - Majovsky, P. AU - Trujillo, M. AU - Zurbriggen, M. D. AU - Hoehenwarter, W. AU - Quint, M. AU - Calderón Villalobos, L. I. A. VL - 8 UR - https://www.nature.com/articles/ncomms15706 DO - 10.1038/ncomms15706 AB - Auxin is a small molecule morphogen that bridges SCFTIR1/AFB-AUX/IAA co-receptor interactions leading to ubiquitylation and proteasome-dependent degradation of AUX/IAA transcriptional repressors. Here, we systematically dissect auxin sensing by SCFTIR1-IAA6 and SCFTIR1-IAA19 co-receptor complexes, and assess IAA6/IAA19 ubiquitylation in vitro and IAA6/IAA19 degradation in vivo. We show that TIR1-IAA19 and TIR1-IAA6 have distinct auxin affinities that correlate with ubiquitylation and turnover dynamics of the AUX/IAA. We establish a system to track AUX/IAA ubiquitylation in IAA6 and IAA19 in vitro and show that it occurs in flexible hotspots in degron-flanking regions adorned with specific Lys residues. We propose that this signature is exploited during auxin-mediated SCFTIR1-AUX/IAA interactions. We present evidence for an evolving AUX/IAA repertoire, typified by the IAA6/IAA19 ohnologues, that discriminates the range of auxin concentrations found in plants. We postulate that the intrinsic flexibility of AUX/IAAs might bias their ubiquitylation and destruction kinetics enabling specific auxin responses. KW - Proteomics A2 - C1 - Proteome Analytics; Molecular Signal Processing; Independent Junior Research Groups ER - TY - JOUR ID - 1894 TI - Comparative expression profiling reveals a role of the root apoplast in local phosphate response JO - BMC Plant Biol PY - 2016 SP - 106 AU - Hoehenwarter, W. AU - Mönchgesang, S. AU - Neumann, S. AU - Majovsky, P. AU - Abel, S. AU - Müller, J. VL - 16 UR - https://dx.doi.org/10.1186/s12870-016-0790-8 DO - 10.1186/s12870-016-0790-8 AB - BackgroundPlant adaptation to limited phosphate availability comprises a wide range of responses to conserve and remobilize internal phosphate sources and to enhance phosphate acquisition. Vigorous restructuring of root system architecture provides a developmental strategy for topsoil exploration and phosphate scavenging. Changes in external phosphate availability are locally sensed at root tips and adjust root growth by modulating cell expansion and cell division. The functionally interacting Arabidopsis genes, LOW PHOSPHATE RESPONSE 1 and 2 (LPR1/LPR2) and PHOSPHATE DEFICIENCY RESPONSE 2 (PDR2), are key components of root phosphate sensing. We recently demonstrated that the LOW PHOSPHATE RESPONSE 1 - PHOSPHATE DEFICIENCY RESPONSE 2 (LPR1-PDR2) module mediates apoplastic deposition of ferric iron (Fe3+) in the growing root tip during phosphate limitation. Iron deposition coincides with sites of reactive oxygen species generation and triggers cell wall thickening and callose accumulation, which interfere with cell-to-cell communication and inhibit root growth.ResultsWe took advantage of the opposite phosphate-conditional root phenotype of the phosphate deficiency response 2 mutant (hypersensitive) and low phosphate response 1 and 2 double mutant (insensitive) to investigate the phosphate dependent regulation of gene and protein expression in roots using genome-wide transcriptome and proteome analysis. We observed an overrepresentation of genes and proteins that are involved in the regulation of iron homeostasis, cell wall remodeling and reactive oxygen species formation, and we highlight a number of candidate genes with a potential function in root adaptation to limited phosphate availability. Our experiments reveal that FERRIC REDUCTASE DEFECTIVE 3 mediated, apoplastic iron redistribution, but not intracellular iron uptake and iron storage, triggers phosphate-dependent root growth modulation. We further highlight expressional changes of several cell wall-modifying enzymes and provide evidence for adjustment of the pectin network at sites of iron accumulation in the root.ConclusionOur study reveals new aspects of the elaborate interplay between phosphate starvation responses and changes in iron homeostasis. The results emphasize the importance of apoplastic iron redistribution to mediate phosphate-dependent root growth adjustment and suggest an important role for citrate in phosphate-dependent apoplastic iron transport. We further demonstrate that root growth modulation correlates with an altered expression of cell wall modifying enzymes and changes in the pectin network of the phosphate-deprived root tip, supporting the hypothesis that pectins are involved in iron binding and/or phosphate mobilization. KW - Proteomics A2 - C1 - Synergy Research Groups; Molecular Signal Processing ER -