The plant hormone auxin is involved in virtually all aspects of plant growth and development. During the last grant period we demonstrated that auxin acts by stimulating the degradation of a family of transcriptional repressers called the AUX/IAA proteins, a process that requires the ubiquitin protein ligase SCFTIR1 and related SCFs. In our most recent studies we have shown that auxin interacts directly with SCFTIR1 or a closely associated protein. We propose that auxin binding promotes the interaction between SCFTIR1 and its' substrates, the AUX/IAA proteins. This is a novel mechanism of hormone action and SCF regulation. The current proposal has three specific aims. The first is to investigate auxin regulation of AUX/IAA degradation. The region of TIR1 that is required for AUX/IAA recognition will be identified. Biochemical experiments will be conducted to identify and characterize proteins that mediate AUX/IAA recognition and in particular the direct target of auxin action will be defined. Further, the structure of the AUX/IAA proteins will be determined in collaboration with my colleague, Dr. L. Chen. In the second aim we will characterize the Arabidopsis root transcriptome. The goals of this aim are to identify downstream targets of AUX/IAA regulation and to compare and contrast auxin regulated transcription in cell types with different auxin growth responses. A number of candidate auxin-response genes have been identified and these will be characterized. In the third aim, we will conduct novel genetic screens for new mutants deficient in auxin response. Our emphasis will be on mutants with severe defects in embryo and root development that are unlikely to be recovered in previous screens. We expect our experiments to provide fundamental new insight into the mechanism of auxin action. Further, our studies indicate that auxin acts through a novel mechanism that involves direct binding to a ubiquitin protein ligase. These results will have significant impact on studies of protein degradation in diverse species including humans.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Special Emphasis Panel (ZRG1-DEV-1 (01))
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Anderson, James J
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Indiana University Bloomington
Schools of Arts and Sciences
United States
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Bagchi, Rammyani; Melnyk, Charles W; Christ, Gideon et al. (2018) The Arabidopsis ALF4 protein is a regulator of SCF E3 ligases. EMBO J 37:255-268
Iglesias, María José; Terrile, María Cecilia; Correa-Aragunde, Natalia et al. (2018) Regulation of SCFTIR1/AFBs E3 ligase assembly by S-nitrosylation of Arabidopsis SKP1-like1 impacts on auxin signaling. Redox Biol 18:200-210
Tao, Sibo; Estelle, Mark (2018) Mutational studies of the Aux/IAA proteins in Physcomitrella reveal novel insights into their function. New Phytol 218:1534-1542
Ligerot, Yasmine; de Saint Germain, Alexandre; Waldie, Tanya et al. (2017) The pea branching RMS2 gene encodes the PsAFB4/5 auxin receptor and is involved in an auxin-strigolactone regulation loop. PLoS Genet 13:e1007089
Shani, Eilon; Salehin, Mohammad; Zhang, Yuqin et al. (2017) Plant Stress Tolerance Requires Auxin-Sensitive Aux/IAA Transcriptional Repressors. Curr Biol 27:437-444
Tal, Iris; Zhang, Yi; Jørgensen, Morten Egevang et al. (2016) The Arabidopsis NPF3 protein is a GA transporter. Nat Commun 7:11486
Lavy, Meirav; Estelle, Mark (2016) Mechanisms of auxin signaling. Development 143:3226-9
Prigge, Michael J; Greenham, Kathleen; Zhang, Yi et al. (2016) The Arabidopsis Auxin Receptor F-Box Proteins AFB4 and AFB5 Are Required for Response to the Synthetic Auxin Picloram. G3 (Bethesda) 6:1383-90
Lavy, Meirav; Prigge, Michael J; Tao, Sibo et al. (2016) Constitutive auxin response in Physcomitrella reveals complex interactions between Aux/IAA and ARF proteins. Elife 5:
Wang, Renhou; Zhang, Yi; Kieffer, Martin et al. (2016) HSP90 regulates temperature-dependent seedling growth in Arabidopsis by stabilizing the auxin co-receptor F-box protein TIR1. Nat Commun 7:10269

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