EFS12- Book of abstracts - Contact

SESSION 1: FUSARIUM – GENETICS, GENOMICS AND SYSTEMS BIOLOGY
The GABA shunt of Fusarium graminearum is
essential for successful colonization of wheat spikes
J. Bönnighausen, J. Bormann, W. Schäfer
Molecular Phytopathology and Genetics, University Hamburg, Germany
E-mail: jakobboennighausen@gmail.com
We evaluated the roles of the non protein amino acid y-amino butyric acid (GABA)
in the Triticum aestivum - Fusarium graminearum interactions. The GABA shunt is
a conserved stress releated pathway which can be used as an alternative route to
bypass two steps of the tricaboxylic acid (TCA) cycle. Its importance for the life
cycle of a fungal pathogen has not been described yet. We constructed single and
double deletion mutants for both GABA transaminases.
Growth of F graminearum wild type with GABA as the sole N-source strongly
induced deoxynivalenol (DON) production. The ΔΔGAT1;2 mutants were unable
to produce DON after GABA induction in culture, instead we observed by HPLC a
massive accumulation of GABA in the mycelium of the double mutant. During
vegetative growth, the ΔΔGAT1;2 mutant showed a decreased resistance against
hydrogen peroxide mediated stress. During wheat infection, the individual single
disruptants were only slightly reduced, whereas the double mutant exhibited a
strong reduction in virulence. During initial infection, ΔΔGAT1;2 mutants were
able to infect the inoculated spikelet, crossed the rachis node and grew into the
rachis. Later, they failed to colonize more than one spikelet above and below the
inoculated one, maintaining only app. 25% of wild type virulence.
Interestingly, no significant differences were found regarding the expression of the
trichothecene biosynthesis genes or the amount of DON during infection.
However, the expression levels of the SSADH genes and a GABA permease
were highly up-regulated in the ΔΔGAT1;2 mutants, suggesting a disturbed
internal GABA level. Concomitantly, the expression level of the citrate synthase
gene, a marker gene for the activity of the TCA cycle, decreased 50%. We
conclude that the GABA shunt modulates the fungal stress response, possibly to
ROS, during wheat colonization and is necessary to maintain the primary energy
metabolism under energy demanding conditions.
Keywords: Fusarium, stress metabolism, GABA
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