in The Department of Plant Sciences
College of Agriculture and Life Sciences, Forbes Building 303,
P.O. Box 210036,
Tucson AZ 85721-0036
(520) 621-1977, FAX (520) 621-7186

Winter Term students

Dr. Martha C. Hawes
College of Agriculture and Life Sciences
Ph.D., University of Kentucky

e-mail: mhawes@u.arizona.edu

Area of Interest:
Plant genes controlling programmed separation of living cells from roots; role of these plant cells in regulating microbial populations colonizing roots.

Research Goals:
Plants of many species systematically shed thousands of healthy cells from each of their root tips daily. Because these cells provide a living interface between the root and the soil, we refer to them as root "border" cells. This seemingly wasteful release of living somatic cells into environment is unique among higher organisms, and its function is unknown. My hypothesis is that border cells provide a selective advantage to the plant by releasing specific chemicals that regulate levels of root- associated microorganisms. Because soil-borne bacteria and fungi comprise not only pathogens that can destroy roots but also beneficial organisms that are crucial for normal plant development, regulating the balance of such microbial populations is crucial to survival. Border cells act as a reservoir of chemicals that can specifically attract or repel microorganisms, as well as activate microbial genes headed for root infection. Mutants of soil-borne microorganisms have been used to demonstrate that, in some cases, recognition of such chemicals from the cells is required for the establishment of root-microbe associations.

The release of living border cells from the growing tip could help plants in a number of ways. For example, specific chemicals in border cells could selectively attract beneficial microorganisms like nitrogen-fixing bacteria to the root. Alternatively, border cell-specific chemicals could repel or be toxic to pathogenic organisms. We have identified border cell- specific genes cell as well as genes that are expressed among separation of border cells from the root. These plant genes are being used to genetically engineer plants with specific alterations in the production of border cells, and in their biological properties. These transgenic plants can be used test the hypothesis that border cells control the susceptibility of plants to infection by symbiotic and pathogenic bacteria and fungi.

Selected Publications:

    Gunawardena U, VanEtten H, Hawes MC 2005. Tissue specific localization of pea (Pisum sativum L.) root infection by Nectria haematocca: Mechanisms and consequences (Plant Physiology, in press)

    Woo HH, Jeong B, Hawes MC 2005 Flavonoids: From Cell Cycle to Biotechnology (Biotechnology Letters, in press)

    Celoy RM, Gardais S, Wen F, Hawes MC 2004. Altered structure, composition, and biological activity of root exudates in transgenic roots with altered root cap gene expression. American Phytopathological Society, Proceedings.

    J.E. Hubbard, M. Schmitt, M. McClure, P. Stock, and M.C. Hawes. 2004. Characterization of root exudate induced quiescence in parasitic, entomophathogenic, and free-living nematode species. Nematology (in press)

    Wen F, Gong FC, Galbraith G, Woo HH, Hawes MC 2004. Border cell specific gene expression. American Phytopathological Society, Proceedings.

    Woo HH, Hirsch AM, Hawes MC 2004. Proceedings of 5th International Symposium. Biotechnology of Natural and Agricultural Products, Daegu University, Korea.

    Zhu Y, Wen F, Zhao X, Hawes MC 2004. Correlation between localized expression of pectinmethylesterase (PME) and release of root exudates from the root tip. Plant and Soil (in press)

    Wen F, Woo HH, Hirsch AM, Hawes MC 2004. Lethality of inducible, meristem localized ectopic expression of ß-glucuronidase in plants. Plant Molecular Biology Reporter 22: 7-14

    Woo HH, Hirsch AM, Hawes MC 2004. Atltered susceptibility to infection by Sinorhizobium meliloti and Nectria haematococca in alfalfa roots with altered cells cycle. Plant Cell Reports 22: 967-973.

    Zhu Y, Wen F, Zhao X, Hawes MC 2004. Isolation of the promoter of a root cap expressed pectinmethylesterase gene from Pisum sativum L. Plant and Soil 265: 47-59.

    Hawes MC, Woo HH, Wen F 2005. Root border cells: A delivery system for chemicals controlling plant health. Soil Science (in press)

    Woo HH, Faull K, Hirsch AM, Hawes MC 2003 Altered life cycle in Arabidopsis plants expressing a UDP-glucuronosyltransferase from Pisum sativum. Plant Physiology 133: 538-548

    Hawes MC, Bengough GA, Cassab G 2003. Root caps and rhizosphere. J Plant Growth Regulation 21: 827-837

    Farrar J, Hawes MC, Jones D, Lindow S 2003 How roots control the flux of carbon to the rhizosphere. Ecology 84: 827–837

    Gunawardena U, Hawes MC 2002 Role of border cells in localized root infection by pathogenic fungi. Molecular Plant Microbe Interactions 15: 1128-1136.

    Woo HH, Kuleck G, Hirsch AM, Hawes MC 2002 Flavonoids: Signal molecules in plant development Advances in Experimental Medicine and Biology 505: 51-60

    Miyasaka ,S., Hawes, M.C. 2001. Possible role of root border cells in aluminum tolerance in legumes. Plant Physiol 1251978-87

    Woo, H.H., Kuleck, G., Hirsch, A.M., Hawes, M.C. 2001. Flavonoids: Signals in plant development. In "Experimental Medicine and Biology"

    Gunawardena, U., Zhao, X., Hawes, M.C. 2001. Roots: Contribution to the Rhizosphere. Encyclopedia of Life Sciences 1.

    Hawes, M.C., Gunawardena, U., Miyasaka, S., Zhao, X. 2000. The role of root border cells in plant defense. Trends in Plant Sciences 5:128-133.

    Zhao, X., Schmidt, M., Hawes, M.C. 2000. Species-dependent effects of root border cells on nematode chemotaxis and motility. Phytopathol 90: 1239-1245.

    Zhao, X., Misaghi, I., Hawes, M.C. 2000. Stimulation of border cell production in response to increased carbon dioxide levels. Plant Physiol 122: 1-8.

    Wen, F., Zhu, Y., Brigham LA, Hawes MC 1999. Expression of an inducible pectinmethylesterase gene is required for border cell separation from roots of pea. Plant Cell 11:1129-1140.

    Woo HH, Brigham LA, Hawes MC 1999. Detection of low abundance messages by a combination of PCR and ribonuclease protection. Expression Genetics: Differential Display. Pardee A, McClelland M, eds.

    Woo HH, Orbach MJ, Hirsch AM, Hawes MC 1999. Meristem localized inducible expression of a UDP-glycosyltransferase gene is essential for growth and development. Plant Cell 11:1-14.

    Hawes MC, Brigham LA, Wen F, Woo HH, Zhu Y 1998. Function of root border cells: Pioneers in the rhizosphere. Ann Rev Phytopathol 36:311-327.

    Brigham LA, Woo HH, Wen F, Hawes MC 1998. Meristem-specific suppression of mitosis and a global switch in gene expression in the root cap of pea by endogenous signals. Plant Physiol 118:1223-1231.

For more information contact:

Dr. Martha Hawes
University of Arizona
303 Forbes Building
P.O. Box 210036
Tucson, AZ 85721-0036

Office Phone: (520)621-5490
Fax: (520)621-7186

last updated: September 13, 2006
2004 The University of Arizona. All contents copyrighted. All rights reserved.