Molecular aspects of Arabidopsis nonhost resistance to Phakopsora pachyrhizi

  • Molekulare Aspekte der Nichtwirt-Resistenz von Arabidopsis gegen Phakopsora pachyrhizi

Campe, Ruth; Göllner, Katharina (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2014)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2014

Abstract

Arabidopsis expresses nonhost resistance (NHR) to Phakopsora pachyrhizi, the causal agent of Asian soybean rust disease that threatens worldwide soybean cultivation. Nonhost resistance is durable and effective to a broad spectrum of pathogens. Understanding nonhost immunity at the molecular level would likely provide knowledge one could use to make susceptible hosts immune to a given disease. The ABC transporter PEN3 is required for Arabidopsis NHR to several nonadapted pathogens, including P. pachyrhizi. However, PEN3’s molecular function is poorly understood. An in vitro binding screen with protein microarrays delivered 28 proteins which bound to PEN3 and based on their GO annotation were found to be associated with the biotic and abiotic plant stress response. Nine of the proteins represented cellular Ca2+ sensors, including calmodulin (CaM) and several CaM-like proteins. The PEN3-CaM interaction was confirmed in vitro by a CaM overlay assay and pull-down of PEN3 with CaM Sepharose and in vivo by bimolecular fluorescence complementation. Furthermore, the cam7 mutant was shown to be compromised in NHR against P. pachyrhizi and the nonadapted powdery mildew fungus Blumeria graminis f. sp. hordei. This study thus provides a novel link between Ca2+ signaling and Arabidopsis NHR. Furthermore, I investigated changes in mRNA transcript accumulation in Arabidopsis upon treatment with P. pachyrhizi uredospores and germination fluid. This approach revealed P. pachyrhizi induces marker genes for defense to necrotroph pathogens, asking whether one can consider the ostensible biotroph a "heminecrotroph" pathogen.

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