The plant hormone auxin regulates virtually every aspect of plant growth and development. Much of this control occurs by auxin regulating the fundamental processes of cell division, cell expansion, and cell differentiation. Given the prominent role of auxin in these basic cellular events, it is hardly surprising that plant biologists have long been intrigued by this hormone and have compiled an enormous amount of physiological data concerning the responses of plants to applied auxin. Over the past decade, molecular insight into the molecular mechanisms underlying auxin signaling has been obtained, with the SCFTIR1 ubiquitin-ligase complex emerging as a central regulator. In response to auxin, SCFTIR1 catalyzes the ubiquitin-mediated degradation of members of the Aux/IAA protein family. The degradation of these negative regulators of auxin response derepresses the pathway, resulting in auxin-mediated changes in gene expression and plant growth and development. We are using genetic, molecular, and biochemical approaches with Arabidopsis to investigate how SCFTIR1 activity is regulated.
A second project in the Gray lab is focused on elucidating the function of Small Auxin Up-Regulated (SAUR) genes. SAURs comprise a large gene family found in all plants. These genes are rapidly induced in response to an auxin stimulus, but what role they play in auxin-mediated growth and development has remained elusive. Utilizing multiple reverse genetic strategies, we have found that SAUR proteins play an important role in auxin-mediated cell expansion. We are currently taking several approaches to elucidate the mechanisms by which SAURs control plant growth.
Lastly, together with the labs of Jerry Cohen and Adrian Hegeman in the Department of Horticulture, we are developing robust methods for measuring plant protein turnover rates utilizing stabile isotope metabolic labeling (2H2O, 15N, or 13CO2) and mass spectrometry.
Spartz, A.K., S.H. Lee, J.P. Wenger, N. Gonzalez, H. Itoh, D. Inze, W.A. Peer, A.S. Murphy, P. Overvoorde, and W.M. Gray. 2012. The SAUR19 subfamily of SMALL AUXIN UP RNA genes promote cell expansion. Plant J. 70:978-90.
Franklin, K.A., S.H. Lee, D. Patel, V. Kumar, A.K. Spartz, C. Gu, S. Ye*, P. Yu*, G. Breen, J. D. Cohen, P.A. Wigge, and W.M. Gray. 2011. PHYTOCHROME INTERACTING FACTOR 4 regulates auxin biosynthesis at high temperature. Proc. Natl. Acad. Sci. USA. 108:21231-5.
Yang, X.Y., W.P. Chen, A.K. Rendahl, A.D. Hegeman, W.M. Gray, and J.D. Cohen. 2010. Measuring the turnover rates of Arabidopsis proteins using deuterium oxide: an auxin signaling case study. Plant J. 63:680-695.
Parry, G., L.I. Calderon-Villalobos, M. Prigge, B. Peret, S. Dharmasiri, H. Itoh, E. Lechner, W.M. Gray, M. Bennet, and M. Estelle. 2009. Complex regulation of the TIR1/AFB family of auxin receptors. Proc. Natl. Acad. Sci. USA. 106: 22540-22545.
Quint, M., L.S. Barkawi, K.-T. Fan, J.D. Cohen, and W. M. Gray. 2009. Arabidopsis IAR4 modulates auxin response by regulating auxin homeostasis. Plant Physiol. 150: 748-58.
Zhang, W., H. Ito, M. Quint, H. Huang, L.D. Noel, and W.M. Gray. 2008. Genetic Analysis of CAND1-CULl Interactions in Arabidopsis Supports a Role for CAND1-Mediated Cycling of the SCFTIR1 Complex. Proc. Natl. Acad. Sci. USA. 105: 8470-8475.
Harmon, F., T. Imaizumi, and W.M. Gray. 2008. CUL1 regulates TOC1 protein stability in the Arabidopsis circadian clock. Plant J. 55: 568-579.
Quint, M. and W.M. Gray. 2006. Auxin signaling. Curr. Opin. in Plant Biol. 9: 448-453.
Ito, H, and W.M. Gray. 2006. A gain-of-function mutation in the Arabidopsis pleiotropic drug resistance transporter PDR9 confers resistance to auxinic herbicides. Plant Physiol. 142: 63-74.
Quint, M., Ito, H., Zhang,W., and W.M. Gray. 2005. Characterization of a novel temperature-sensitive allele of the CUL1/AXR6 subunit of SCF ubiquitin-ligases. Plant J. 43:371-383.
Chuang, H.-w., Zhang, W., and W.M. Gray. 2004 Arabidopsis ETA2, an Apparent Ortholog of the Human Cullin-Interacting Protein CAND1, Is Required for Auxin Responses Mediated by the SCF TIR1 Ubiquitin Ligase. Plant Cell, 16: 1883-1897.
Gray, W.M., P.R. Muskett, H.-w. Chuang, and J. E. Parker Arabidopsis SGT1b is required for SCFTIR1 -mediated auxin response. Plant Cell, 15:1310-1319.
Gray, W.M., S. Kepinski, D. Rouse, O. Leyser, and M. Estelle. 2001. Auxin Regulates SCFTIR1 -Dependent Degradation of Aux/IAA proteins. Nature 414, 271-276
Gray, W.M., Hellmann, H., Dharmasiri, S., and Estelle, M.. (2002). Role of the Arabidopsis RING-H2 protein RBX1 in RUB modification and SCF function. Plant Cell 14(9) 2137-2144.
Schwechheimer C., G. Serino, J. Callis, W.L. Crosby, S. Lyapina, R.J. Deshaies, W.M. Gray, M. Estelle, and X.W. Deng. 2001. Interactions of the COP9 Signalosome with the E3 Ubiquitin Ligase SCFTIR1 in Mediating Auxin Response. Science 292, 1379-1382.
Gray, W.M., and M. Estelle. 2000. Function of the ubiquitin-proteasome pathway in auxin response. Trends Biol. Sci. 25: 133-138.
Gray, W.M., J.C. del Pozo, L. Walker, L. Hobbie, E. Risseeuw, T. Banks, W.L. Crosby, M. Yang, H. Ma, and M. Estelle. 1999. Identification of an SCF ubiquitin-ligase complex required for auxin response in Arabidopsis thaliana. Genes &; Dev. 13: 1678-1691.
Gray, W.M., A. Ostin, G. Sandberg, C.P. Romano, and M. Estelle. 1998. High temperature promotes auxin-mediated hypocotyl elongation in Arabidopsis. Proc. Natl. Acad. Sci. USA. 95: 7197-7202.
Ruegger, M., E. Dewey, W.M. Gray, L. Hobbie, J. Turner, and M. Estelle. 1998. The TIR1 protein of Arabidopsis functions in auxin response and is related to human SKP2 and yeast Grr1p. Genes & Dev. 12:198-207.