Roles of the Cpc1 regulator of the cross-pathway control in the Verticillium plant pathogens

by Christian Timpner
Doctoral thesis
Date of Examination:2013-10-23
Date of issue:2014-06-20
Advisor:Prof. Dr. Gerhard Braus
Referee:Prof. Dr. Gerhard Braus
Referee:Prof. Dr. Andrea Polle
Persistent Address: http://dx.doi.org/10.53846/goediss-4560

 

 

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Abstract

English

Verticillium longisporum is a soil-borne fungal pathogen of oilseed rape (Brassica napus). Infection is initiated by hyphae from germinating microsclerotia which invade the plant vascular system through penetration of the fine roots. Most of its life cycle, V. longisporum is confined to the vascular system of the plant. The xylem fluid provides an environment with limited carbon sources and imbalanced amino acid supply, which requires that V. longisporum induces the cross-pathway control of amino acid biosynthesis. VlCPC1 encodes the conserved transcription factor of the cross-pathway control. RNA-mediated gene silencing reduced the expression of the two CPC1 isogenes (VlCPC1-1, VlCPC1-2) of the allodiploid V. longisporum up to 85%. The silenced mutants were highly sensitive to amino acid starvation and the infected plants showed significantly less symptoms such as stunting or early senescence in oilseed rape plant infection assays. Consistently, deletion of single CPC1 of the haploid V. dahliae resulted in strains, which are sensitive to amino acid starvation and cause strongly reduced symptoms in the plant-host tomato (Solanum lycopersicum). The allodiploid V. longisporum and the haploid V. dahliae are the first phytopathogenic fungi, which were shown to require CPC1 for infection and colonization of their respective host plants oilseed rape and tomato. We investigated secondary metabolism as it might be required for pathogenicity. The key regulator of secondary metabolism LAE1 was further investigated. Silenced mutants reduced the expression of the two isogenes (VlLAE1-1, VlLAE1-2) up to 80% and showed milder symptoms on plants. The corresponding deletion in V. dahliae did not show any contribution to pathogenicity. Furthermore a secreted lipase was silenced as well. The efficiency of silencing reached around 80% and the mutants showed a reduced pathogenicity on oilseed rape in plant infection assays.
Keywords: Verticillium; CPC1
 
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