The plant hormone auxin is involved in virtually all aspects of plant growth and development. Over the years we and others have demonstrated that auxin acts by stimulating the degradation of a family of transcriptional repressors called the Aux/IAA proteins, through the action of the ubiquitin protein ligase SCFTIR1/AFB. Although this basic pathway is well established, we still know very little about how auxin regulates plant growth and development. Strikingly, auxin-regulated genes differ dramatically between cell types and organs, consistent with the diverse roles of the hormone. The basis for this specificity is unknown. Similarly, the activities of the Aux/IAA and ARF proteins are poorly characterized and the gene regulatory networks (GRNs) that mediate various auxin-regulated growth processes have not been defined. Finally, we know little about how auxin signaling is integrated with other environmental and genetic signaling pathways. Recently we discovered that one member of the TIR1/AFB family of auxin co-receptors, AFB1, has a key role in a non-genomic rapid auxin response in the root. This was a surprising result because the TIR1/AFB proteins are known to function in transcriptional regulation. We also demonstrated that AFB1 is highly enriched in the cytoplasm and propose that it is this feature that leads to its specialized role in the rapid response. In this proposal, we request funds to purchase a Keyence BZX 810 fluorescent microscope. This instrument is ideally suited to assess the growth of Arabidopsis seedlings in real time. We have already demonstrated its utility in studies of the role of auxin in rapid changes in root growth using an instrument at the Salk Institute. We expect that the microscope will allow us to rapidly make progress in our understanding of a novel and surprising function of the AFB1 protein

Public Health Relevance

Protein homeostasis is a central aspect of cellular regulation. Defects in pathways that mediate protein stability and degradation including the chaperones and the ubiquitin proteasome pathway contribute to many disease processes including cancers. This study will advance our understanding of the protein homeostasis in cell function and well as the role of cullin-ring based E3 ligases in growth and development.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Phillips, Andre W
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University of California, San Diego
Schools of Arts and Sciences
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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
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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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