UC Berkeley

This Dissertation presents a comprehensive study of how oomycete pathogens are recognized by the plant model organism Arabidopsis thaliana. The key molecular factors in this study include pathogen derived effector molecules, and plant disease resistance genes; specifically, the effector, Arabidopsis thaliana recognized 1 (ATR1) and cognate plant resistance gene, Recognition of Peronospora parasitica 1 (RPP1). Presented data, gathered using genetics, biochemistry, structural biology, natural history and human logic, provide insights into molecular basis for recognition of ATR1 by RPP1. It is demonstrated that the in planta physical association between ATR1 and RPP1 leads to activation of plant immunity. The main regions of RPP1 responsible for effector recognition and downstream activation of immunity are elucidated. Examination of natural variation among ATR1 and RPP1 variants and subsequent heuristic mutational analyses yielded proteins with reversed activity, allowing manipulating the plant to expand its range of pathogen recognition. The 3-D structure of ATR1 was determined and showed that several independent regions could be recognized by RPP1 variants, illustrating adaptive components in plant immunity. Finally, the observed interactions between 83 different Arabidopsis sub-species and 5 strains of its native obligate oomycete pathogen provide show multi-level regulations of host / pathogen interactions, including developmental control of resistance in the host, and the ability of pathogen to suppress recognition of effectors and plant immunity.