Functional genomics of leaf epidermis in response to pathogen attack.

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Plant diseases have a devastating impact on agricultural production and food supply every year.  During pathogen attack however, most plants mount a complex of physical and chemical defence strategies to ward off attempted invasions.  On the plant surface (epidermis), pathogen infection failures are often associated with localized host cell wall fortifications (papillae) underneath the sites of attempted penetration.  Papilla formation has long been recognized as an ancient, basal plant resistance to pathogen penetration attempts.  Hence, major efforts have been devoted to understanding the mechanisms of penetration resistance.  My previous studies have shown an effective, near-immune penetration resistance at attempted penetration sites on wheat leaf epidermis following attack by the powdery mildew fungus.  From this material, we have isolated ~3,000 epidermal genes, many of which we have characterized to show a broad repertoire of genetic defenses unleashed during the early stage of pathogen attack.  The proposed research will focus on comparative and complementary analyses between a well-characterized wheat-powdery mildew pathosystem and a novel Arabidopsis-Colletotrichum pathosystem to address fundamental questions in epidermal penetration resistance.  The overall strategy will involve i) the molecular isolation, identification and functional characterization of a full set of core elements in wheat leaf epidermis that mediate penetration resistance, and ii) genetic confirmation and manipulation of epidermal resistance using Arabidopsis as a model plant.  This research involves the use of pathogenic, molecular and genomic methods.  Successful completion of this study will contribute tremendously to our understanding of the genetic and cellular mechanisms that control early defenses in the leaf epidermis, and the output of the research could generate new strategies for engineering plant disease resistance.