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DIVISION OF PLANT
PATHOLOGY & MICROBIOLOGY |
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Dr.
Ho-Hyung Woo e-mail: hhwoo@ucla.edu | ||
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Area of Interest: | ||
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| Research
Goals: Cell proliferation is a fundamental process, which is highly regulated particularly in the course of development and maintenance of multicellular organisms. It is subject to many external and internal perturbations. Certain endogenous chemicals regulate the cell cycle and its control processes. In plants several thousand glycosylated chemicals have been identified. Glycosylated secondary metabolites include flavonoids, anthocyanins, monoterpenes, and plant hormones. Glycosylation of phytochemicals invariably results in enhanced water solubility and lower chemical reactivity. Glycosylated compounds are thought of as transportable storage compounds or waste/ detoxification products lacking physiological activity. These conjugates can be stored in vacuoles or cell walls for long time intervals. In the case of phytohormones, such as auxin, cytokinin, gibberellin, abscisic acid, jasmonate and brassinolide, etc., conjugates might also act as reversible deactivated storage forms. Conjugation thus may be important in 'homeostasis' for the regulation of physiologically active hormone levels. In other cases, conjugation of hormones might accompany or introduce irreversible deactivation. New work from our laboratory suggests that genetic alteration of glucuronide metabolism resulted in the accumulation of flavonoid-like compound X in a UDP-Glucuronosyltransferase (PsUGT1)-mutant of alfalfa. The results indicate that the activity of flavonoid-like compound X is likely controlled by cellular glycosylation. We have found that PsUGT1 functions by controlling cellular levels of the active form of compound X. More than 4,000 different flavonoids, which are widely distributed in higher plants, have been identified. Flavonoids are involved in numerous functions in vascular plants, such as a filter for ultraviolet light and external chemical signals for symbiotic nitrogen fixation. Flavonoid phytoalexins act in disease defense mechanisms. Anthocyanidins and their glycosides, which accumulate mainly in the inner epidermis of the petal just prior to opening of the flower bud, attract insects and other agents for pollination. Flavonoids also act as internal physiological regulators or chemical messengers in the plant, and for these functions, relatively small amounts are effective. Flavonoids such as quercetin and kaempferol have been shown to function as auxin transport inhibitors. In vitro enzyme assay using recombinant PsUGT1 enzyme showed that a single compound (i.e. compound X) became glycosylated by UDP-14C-glucuronic acid. HPLC purification and mass spectrometry suggested that compound X is most likely a flavonoid, which is the acceptor for UDP-glucuronic acid. Previously, some flavonoids were proposed as negative regulators for polar auxin transport. However, there is no direct evidence about the regulatory role of flavonoids in auxin transport. During the next five years, I intend to characterize the chemical nature of compound X, its receptor and characterization of compound X-receptor relations. | ||
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| Selected Publications:
Ho-Hyung Woo, B.R. Jeong, M.C. Hawes, A.M. Hirsch. 2005, Characterization of families of Arabidopsis genes for glucuronide metabolism-regulated auxin distribution. Submitted. Ho-Hyung Woo, B.R. Jeong,
M.C. Hawes. 2005, Flavonoids: from cell cycle regulation to biotechnology.
Biotechnology Letters. 27, 365-374. Ho-Hyung Woo, A.M. Hirsch, M.C. Hawes, 2004, Altered susceptibility to infection by bacteria and fungi in alfalfa roots with altered cell cycle. Plant Cell Reports. 22, 967-973. F.Wen, Ho-Hyung Woo,
A.M. Hirsch, M.C. Hawes, 2004, Lethality of inducible, meristem-localized
ectopic b-glucuronidase expression in plants. Plant Mol. Biol. Reporter.
22, 7-14. Ho-Hyung Woo, Gary Kuleck, Ann M. Hirsch, and Martha C. Hawes 2002. Flavonoids: Signal molecules in plant development. In 'Flavonoids in cell function', Advances in experimental medicine and biology, vol. 505, 51-60. LeRoy, A., Potter, E., Ho-Hyung Woo, Heber, D. and Hirsch, A.M. 2002. Characterization and Identification of Alfalfa and Red Clover Dietary Supplements Using a PCR-Based Method, Journal of Agricultural and Food Chemistry. 50, 18, 5063-5069. Ho-Hyung Woo, Marc Orbach, Ann M. Hirsch and Martha C. Hawes, 1999, Meristem-localized inducible expression of a UDP-Glycosyltransferase gene is essential for growth and development in pea and alfalfa, The Plant Cell. 11 (12): 2303-2316. LA Brigham, Ho-Hyung Woo, F Wen and MC Hawes, 1998, Meristem-specific suppression of mitosis and a global switch in gene expression in the root cap of pea by endogenous signals. Plant Physiology, 118: 1223-1231. MC Hawes, L.A Brigham, F Wen, Ho-Hyung Woo and Y Zhu, 1998, Function of root border cells in plant health: pioneers in the rhizosphere. Annual Review of Phytopathology 36: 311-327. Ho-Hyung Woo and MC Hawes, 1997, Cloning of genes whose expression is correlated with mitosis and localized in dividing cells in root caps of Pisum sativum L. Plant Molecular Biology, 35: 1045-1051. Ho-Hyung Woo, LA Brigham and MC Hawes, 1995, Molecular cloning and expression of mRNAs encoding H1 histone and an H1 histone-like sequences in root tips of pea (Pisum sativum L.), Plant Molecular Biology 28 1143-1147. LA. Brigham, Ho-Hyung Woo, MS Nicoll and MC Hawes, 1995, Differential expression of proteins and mRNAs from border cells and root tips of Pisum sativum. Plant Physiology. 109 (2) 457-463.LA Brigham, Ho-Hyung Woo and MC Hawes, 1995, Root border cells as tools in plant cell studies; In "Methods in Cell Biology", Vol. 49 377-387, Academic press. Ho-Hyung Woo, LA Brigham and MC Hawes, 1994, Primary structure of the mRNA encoding a 16.5-kDa ubiquitin-conjugating enzyme of Pisum sativum. Gene. 148 369-370. | ||
| Publications in
Molecular Techniques:
Ho-Hyung Woo, 2001, Molecular Techniques and Methods, In "http://www.molecularinfo.com/", Los Angeles, CA, USA. Ho-Hyung Woo, LA Brigham and MC Hawes, 1999, Detection of low abundance messages by a combination of PCR and ribonuclease protection, Expression Genetics: Differential Display (Ed. A. Pardee and M. McClelland), Ch.47, pp401-406. Eaton Publishing. Ho-Hyung Woo, 1997, In-cell RT-PCR in a single, detached plant cell. Plant Molecular Biology Manual, Second edition, Section G, Supplement 2, Chapter G4 pp1~8, Kluwer academic publishers, Dordrecht. Ho-Hyung Woo and MC Hawes, 1997, Rapid mapping and subcloning of genomic clones in bacteriophage lamda by PCR. BioTechniques. 22 (5) 822-824. | ||
| Web page for Current
Molecular Techniques: | ||
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| For more information contact:
Dr. Ho-Hyung Woo http://www.bol.ucla.edu/~hhwoo/ Office Phone: (520)621-3917 | ||
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