Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2007
Publication Date: 7/1/2007
Citation: Wang, X., Replogle, A., Davis, E., Mitchum, M. 2007. The tobacco Cel7 gene promoter is auxin-responsive and locally induced in nematode feeding sites of heterologous plants. Molecular Plant Pathology. 8:423-436. Interpretive Summary: Cyst and root-knot nematodes are parasites of plant roots that cause significant economic damage to many agricultural crops. In order for a nematode to successfully parasitize a root a specific change in the structure and function of plant cells must occur to produce a specialized site for the nematode to feed. How the change in the plant cell activity is initiated by the nematode is the subject of our current research. We have identified several plant genes whose activity is changed by the nematode presence. One of these plant genes encodes an enzyme that modifies the plant cell wall, a response necessary for the formation of the nematode feeding site. This paper describes how the activity of this cell wall modifying gene increases in several plant species when nematodes begin to attack the roots. This information has increased our understanding of how nematodes can direct plant gene activities to allow the plant to become a host of the nematode and a source of food. This information may lead to the identification of methods to prevent nematode feeding and damage to crop plants.
Technical Abstract: Emerging evidence suggests that plant cell wall modifying enzymes induced by root-parasitic nematodes play important roles in feeding cell formation. We previously identified a tobacco endo-B-1,4-glucanase (cellulase) gene, NtCel7, that was strongly induced in both root-knot and cyst nematode feeding cells. To further characterize the developmental and nematode-responsive regulation of NtCel7, we isolated the NtCel7 promoter and analyzed its expression over a time course of nematode infection and under a variety of conditions in transgenic soybean and tomato hairy roots and in transgenic Arabidopsis that contained a NtCel7 promoter-GUS construct. Histochemical analyses of transgenic plant materials revealed that the NtCel7 promoter exhibited a unique organ-specific expression pattern during plant development suggestive of important roles for NtCel7 in both vegetative and reproductive growth. In all plant species tested, strong GUS expression was observed in root tips and lateral root primordia of uninfected roots with weaker expression in the root vasculature. Further analyses of transgenic Arabidopsis plants revealed a cell-type specific expression pattern in shoot and root meristems and the vasculature of most organs during plant development. We also determined that the NtCel7 promoter was induced by auxin. Moreover, strong GUS activity was observed in both cyst and root-knot nematode induced feeding sites in transgenic roots of soybean, tomato, and Arabidopsis. The conserved developmental and nematode-responsive expression of the NtCel7 promoter in heterologous plants indicates that motifs of this regulatory element play a fundamental role in regulating NtCel7 gene expression within nematode feeding sites and that this regulation is mediated by phytohormones.