Effects of Verticillium factors on cell biology and development of Arabidopsis thaliana and Brassica napus roots
Final Report Abstract
Confocal Laser Scanning microscopy was used to visualize GFP-tagged Verticillium longisporum strain 43 in the plant tissue. Analyses of infected roots showed that V. longisporum exclusively entered the vascular system at zones without a fully established endodermis like the root tip area and developing root primordia. Hyphae that infected the root via the root tip or root primordia reached the protoxylem in the differentiation zone and colonized the xylem in acropetal and basipetal direction. We hypothesized that leaf chloroses indicate early senescence of infected leaves. Cytokinin measurements and analyses of cytokinin oxidases indicated that Verticillium may actively induce decreases in cytokinin levels to induce early senescence. Senescing tissue provides easy access to nutrients during the saprophytic phase of the fungus‟ life cycle. We expected that artificial increases in cytokinin content will prevent or reduce early senescence and inhibit fungal proliferation in leaves. Stabilization of cytokinin homeostasis both by pharmacological treatments and by a genetic approach resulted in reduced senescence and inhibition of fungal proliferation. Microscopical analyses of chloroses near vascular bundles revealed transdifferentiation of bundle sheath cells into tracheary elements in Verticillium infested Arabidopis. This observation prompted us to investigate the role of de novo xylem formation during fungal infection. Expression analysis of VND transcription factors during the disease-cycle and the study of pathogen-inducible VND loss of function mutants revealed the key role of VND7 for Verticillium induced transdifferentiation. We hypothesized that newly built xylem is a plant response to a vascular pathogen to avoid wilting. Interestingly, infected wild-type plants exhibiting de novo xylem formation showed higher drought resistance than non-infected plants. Suppression of transdifferentation in pathogen inducible VND loss of function mutants resulted in loss of increased drought-resistance.
Publications
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(2010) Silencing of Vlaro2 for chorismate synthase revealed that the phytopathogen Verticillium longisporum induces the crosspathway control in the xylem. Appl Microbiol Biot 85: 1961-1976
Singh S, Braus-Stromeyer SA, Timpner C, Tran VT, Lohaus G, Reusche M, Knüfer J, Teichmann T, von Tiedemann A, Braus, GH
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(2011) Analyse der Verticillium longisporum induzierten Seneszenz und Transdifferenzierung in Arabidopsis thaliana. PhD Thesis
Michael Reusche
