 |
|
|
|
|
|
|
|
|
 |
 |
 |
 |
 |
 |
 |
 |
|
|
Tim Hall received a B.Sc. (1962) in Botany and Ph.D. (1965) in Plant Physiology from the University of Nottingham, England. After a postdoctoral fellowship at the University of Minnesota-St. Paul, he accepted an appointment at the University of Wisconsin-Madison where he rose to full Professor. From 1980-1984 he established and directed the Agrigenetics Advanced Research laboratory at Madison, where he participated in the creation of the first transgenic plants expressing a developmentally regulated gene. He joined the Department of Biology at Texas A&M University in 1984 as Distinguished Professor and Department Head. He is currently Director of the Institute of Developmental and Molecular Biology. Hall lab: http://www.idmb.tamu.edu/hallslab/ |
Tim Hall 3155 TAMU Office: Lab: Fax: 979-862-4098 |
||||
| Research Interests
My lab studies the basis of gene regulation in plants, especially the involvement of chromatin in spatial control of expression and in gene silencing. Dicots: Our studies on gene regulation in dicots have focused on the seed storage proteins, and especially the b-phas gene which encodes one of the polypeptides of the most abundant protein, phaseolin, present in the bean, Phaseolus vulgaris. We pioneered an understanding of the subunit nature of phaseolin and studied the attachment of glycans to the polypeptide backbone that give rise to various glycoforms of the native protein. We developed cell-free protein synthesis systems from plants capable of producing defined proteins, and cloned plant cDNA and genomic DNA sequences that first revealed the presence of plant introns. Together with Dr. John Kemp's group, we were the first to successfully transfer and express a plant gene across wide taxonomic boundaries by expressing phaseolin in the seed of transgenic tobacco plants as a result of Ti-plasmid mediated gene transfer. Many different b-phas gene constructs for studies on cis- and trans-acting functions related to tissue-specific and temporal regulation have been made. We found that a tightly (rotationally and translationally) positioned nucleosome is present over the TATA region of the b-phas promoter in vegetative tissues of transgenic tobacco that precludes binding of TBP (hence, preventing transcription) but have now shown that expression can be activated in vegetative tissues by a two-step process that involves (1) factor-mediated chromatin remodeling and (2) abscisic acid-mediated activation. Recently, we have obtained evidence that a phosphatase has a negative regulatory role in vegetative tissues. The β-phas system has been moved to Arabidopsis and changes in histone modification associated with the potentiation and activation events are being studied using chromatin immunoprecipitation assays (ChIPs) . The use of a stably transformed estradiol-inducible system to generate the synthesis of PvALF (the transcription factor responsible for initiating the potentiation step) in leaves, together with exogenous supply of abscisic acid, is providing new insight to the molecular mechanisms involved in transcriptional activation. Complementary studies are underway using the model legume, Medicago truncatula. Gene Silencing in Monocots and Arabidopsis: Initial work involved sorghum, and the isolation and characterization of genomic and cDNA clones encoding kafirin, the major seed protein. However, transformation and regeneration of rice was easier and, with funding from the Rockefeller Foundation we produced plants transgenic for a range of constructs using both electroporation of protoplasts and microprojectile bombardment of embryogenic callus. Unfortunately, careful molecular characterization of the transgene as well as of expression levels revealed that the gene inserts were typically rearranged and that expression of the gene of interest was often absent in progeny plants. As a result, we have actively investigated the causes of gene silencing and methods for its avoidance. Since 1994, with industrial support, we have developed our own Agrobacterium-based vectors and have developed various procedures for rice transformation. These largely overcome the problem of gene rearrangement, but understanding gene silencing mechanisms remains an active research goal. We have isolated and partially characterized two DNA methyltransferase genes from rice (OsMET1-1 and OsMET1-2) and are currently exploring plant viability and function after RNAi-mediated knockout of gene function in rice. RNAi has also been used to knockout function of SET domain genes in Arabidopsis and the consequences are being evaluated. |
|||||
|
Xin Zhou , Raul Carranco , Stanislav Vitha and Timothy C. Hall 2005. The dark side of green fluorescent protein. New Phytologist 168: 313-321 Teerawanichpan, P., Chandrasekharan, M.B., Jiang, Y., Narangajavana, J. and Hall, T.C. 2004. Characterization of two rice DNA methyltransferase genes and RNAi-mediated restoration of promoter activity in silenced rice callus. Planta 218: 337-349. Grace, M.L., Chandrasekharan, M.B., Hall, T.C. and Crowe, A.J. 2004. Sequence and spacing of TATA box elements are critical for accurate initiation of the ß-phaseolin promoter. J. Biol. Chem. 279: 8102-8110. Zhou, X, Chandrasekharan, M.B. Hall, T.C. 2004. High rooting frequency and functional analysis of GUS and GFP expression in transgenic Medicago truncatula A17. New Phytol. 162: 813-822. Ng, D. W-K, Chandrasekharan, M.B., Hall, T.C. 2004. The 5' UTR negatively regulates expression from the ABI3 promoter. Plant Mol. Biol. 54: 25-38. Carranco, R., Chandrasekharan, M.B. Townsend, J.C. and Hall, T.C. 2004. Interaction of PvALF and VP1 B3 domains with the ß-phaseolin promoter. Plant Mol. Biol. 55: 221-237. Click a cover to view the article:
|
