Biochemistry

Thomas Guilfoyle

Professor of Biochemistry

E-mail:guilfoylet@missouri.edu

Office: 10 Schweitzer Hall

Mail: Biochemistry
117 Schweitzer Hall
University of Missouri
Columbia, MO 65211

Phone: (573) 882-7648

Fax: (573) 882-5635

Lab: (573) 882-7300

Educational background

Curriculum vitae

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Notable honors and service

• American Association for the Advancement of Science, Fellow (2007)
• American Society of Plant Biologists
  • Elected Fellow (2007)
  • Charles Reid Barnes Life Membership Award (2009)
• American Association for Advancement of Science, Electorate Nominating Committee
• Editorial Boards:
  
  • The Plant Cell, Co-Editor
  • Plant Methods
  • Plant Physiology, Associate Editor (previous)
  • Plant Molecular Biology (previous)

Research summary

Our current research is focused on understanding how specific domains in ARF and Aux/IAA proteins function in auxin-regulated transcription.

Research description

Auxin mediates a wide variety of plant growth and developmental processes, including organ patterning, lateral root initiation, stem and root elongation, vascular tissue formation and differentiation, apical dominance, and tropisms. Most of these processes are likely initiated by specific patterns of gene expression in response to localized changes in auxin concentration. Genes have been identified that are rapidly up-regulated or down-regulated with cell/tissue/organ specificity in response to auxin. Early auxin genes respond within minutes after auxin stimulation and do not require protein synthesis for a response. Aux/IAAs, GH3s, and SAURs are examples of early auxin response genes. Analysis of early auxin gene promoters has allowed us to identify cis-elements [i.e., Auxin Response Elements or AuxREs with the sequence TGTCTC] that confer auxin responsiveness and trans-factors [i.e., Auxin Response Factors or ARFs] that bind with specificity to AuxREs.

ARF genes and proteins. There are 22 genes in Arabidopsis that are predicted to encode ARF proteins [i.e., referred to as ARF1 to ARF22]. ARF proteins range in size from about 70 to 130 kDa and contain conserved N-terminal DNA-binding domains [DBDs] and C-terminal dimerization domains [CTDs], with the exception of ARF3 and ARF17, which lack a canonical CTD. ARFs also contain nonconserved regions, just C-terminal to the DBD, which function as activation [AD] or repression [RD] domains. ARF DBDs are related over a stretch of about 120 amino acids to a conserved B3 domain found in the DBDs of a variety of other plant transcription factors. ARF dimerization domains are composed of motifs III and IV and are related in amino acid sequence to motifs III and IV in the dimerization domains of Aux/IAA proteins. These motifs facilitate homotypic and heterotypic interactions among ARF and Aux/IAA proteins. The AD/RDs of ARFs have biased amino acid sequences, and those that are Q-rich function as ADs [i.e., ARF5, -6, -7, -8, -19] in protoplast transfection assays. The remaining ARFs function as repressors, at least in transfected plant protoplasts. Mutations in ARF genes have provided insight into auxin-dependent processes that ARF transcription factors regulate.

Aux/IAA genes and proteins. Arabidopsis contains 29 Aux/IAA genes and many of these are early auxin genes. Some are induced within 5-10 minutes following auxin treatment. Aux/IAA genes encode proteins of 20-35 kDa that, in general, share four motifs [i.e., I, II, III, and IV] of amino acid sequence similarity. Several Aux/IAA proteins have been shown to have short half-lives [i.e., 5-10 minutes] and are localized to the nucleus. While Aux/IAA proteins do not appear to bind DNA in a selective manner, they, nevertheless, function as active repressors by dimerizing with ARF activators on auxin-responsive genes. A number of dominant or semidominant auxin response mutants have been identified that have amino acid substitutions within motif II of Aux/IAA proteins. These mutations result in stabilization of Aux/IAA proteins, and mutant plants show alterations in auxin sensitivity and responses, including increased resistance to exogenous auxin, abnormalilties in lateral root and root hair formation, and defects in root and hypocotyl gravitropism. In some cases, loss-of-function arf mutants and gain-of-function aux/iaa mutants have similar phenotypes, suggesting that these ARF and Aux/IAA proteins may function as partners in regulating auxin response genes in specific cells/tissues or at specific stages of development.

Interplay of ARFs and Aux/IAA proteins in regulating auxin response genes. ARF and Aux/IAA proteins are thought to function together in regulating expression of early auxin genes. ARF activators bind with specificity to TGTCTC AuxREs and dimerize with Aux/IAA repressors when auxin concentrations are low, resulting in dominant, active repression. When auxin concentrations are elevated, Aux/IAA repressors become increasingly unstable, resulting in their decreased abundance and release from the ARF activators. This in turn leads to derepression/activation of the auxin response genes. Potentiation of activation occurs when closely related ARF activators are recruited to the AuxRE via CTD dimerization. Our current research is focused on understanding how specific domains in ARF and Aux/IAA proteins function in auxin-regulated transcription.

Selected publications

Wang S, Tiwari SB, Hagen G, Guilfoyle TJ (2005) AUXIN RESPONSE FACTOR7 Restores the Expression of Auxin-Responsive Genes in Mutant Arabidopsis Leaf Mesophyll Protoplasts. Plant Cell 17, 1979-1993

Nagpal P, Ellis CM, Weber H, Ploense S, Barkawi LS, Guilfoyle TJ, Hagen G, Alonso JM, Cohen JD, Farmer EE, Ecker JR, and Reed JW (2005) Auxin response factors ARF6 and ARF8 promote jasmonic acid production and flower maturation. Development 132, 4107-4118.

Ellis CM, Nagpal P, Young JC, Hagen G, Guilfoyle TJ, Reed JW (2005) AUXIN RESPONSE FACTOR1 and 2 regulate senescence and floral abscission in Arabidopsis thaliana. Development, 132, 4563-4574.

Guilfoyle TJ (2007) Plant biology: sticking with auxin. Nature 446, 621-622.

Shin R, Burch AY, Huppert KA, Tiwari SB, Murphy AS, Guilfoyle TJ, Schachtman DP (2007) The Arabidopsis transcription factor Myb77 modulates auxin signal transduction. Plant Cell 19, 2440-53

Guilfoyle T.J., Hagen G. (2007) Auxin response factors. Curr. Opin. Plant Biol. 10 (5): 453-60

Li H., Cheng Y., Murphy A., Hagen G., Guilfoyle T.J. (2009) Constitutive repression and activation of auxin signaling in Arabidopsis. Plant Physiol. 149 (3): 1277-88

Employment opportunities

Postdoctoral opportunities

Research areas: Transcriptional control by auxins in plants; plant RNA polymerases.

How to apply:

Electronic submission is encouraged, e-mail to guilfoylet@missouri.edu

Applicants should send CV and names of two references to:
Dr. Thomas Guilfoyle
Biochemistry
117 Schweitzer Hall
University of Missouri
Columbia, MO 65211