Title page for ETD etd-09142011-144211

Type of Document Dissertation
Author Anderson, Ryan Gabriel
Author's Email Address andersrg@vt.edu
URN etd-09142011-144211
Title Identification and functional characterization of RXLR effector proteins that are conserved between downy mildew pathogens and Phytophthora species
Degree PhD
Department Plant Pathology, Physiology, and Weed Science
Advisory Committee
Advisor Name Title
McDowell, John M. Committee Chair
Lawrence, Christopher B. Committee Member
Tyler, Brett M. Committee Member
Westwood, James H. Committee Member
Winkel, Brenda S. J. Committee Member
  • Oomycete
  • effector
  • RXLR
  • plant immunity
  • Hyaloperonospora arabidopsidis
Date of Defense 2011-09-09
Availability unrestricted
Diverse pathogens secrete effector proteins into plant cells to manipulate host cellular processes. The genome of Hyaloperonospora arabidopsidis (Hpa), the causative agent of downy mildew of Arabidopsis, contains at least 134 candidate RXLR effector genes. These genes contain an RXLR motif required for effector entry into host cells. Only a small subset of these candidate effectors is conserved in related oomycetes. Here, we describe a comparative functional characterization of the Hpa RXLR effector HaRxL96 and a homologous gene, PsAvh163, from the soybean pathogen Phytophthora sojae. HaRxL96 and PsAvh163 are induced during early stages of infection and carry a functional RXLR motif that is sufficient for protein uptake into plant cells. Both effectors can suppress or activate immune responses in soybean, Nicotiana, and Arabidopsis. Several SA-responsive defense genes are suppressed in Arabidopsis Col:HaRxL96 and Col:PsAvh163 during an incompatible interaction with Hpa Emoy2. Both effectors are localized to the nucleus and cytoplasm of plant cells. Nuclear localization of both effectors is required for proper virulence functions, including suppression of basal resistance and RPP4-mediated immunity to virulent and avirulent Hpa, respectively. In addition, both effectors interact with plant U-box (PUB) proteins that are conserved between diverse plant species. The targeted PUB proteins are negative regulators of plant immunity in Arabidopsis. These experiments demonstrate that evolutionarily-conserved effectors from different oomycete species can suppress immunity in plant species that are divergent from the source pathogen’s primary host.
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