Fungal Responses to Grazers
by Silvia Caballero Ortiz
Date of Examination:2014-10-01
Date of issue:2014-10-10
Advisor:PD Dr. Marko Rohlfs
Referee:PD Dr. Marko Rohlfs
Referee:Prof. Dr. Stefan Scheu
Persistent Address:
http://dx.doi.org/10.53846/goediss-4725
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Abstract
English
Fungi are organisms that due to their inability of moving are highly exposed to suffer predation. As a consequence, fungi have evolved different defence strategies to keep fungivores in check. Among these strategies, fungi are thought to synthesize secondary metabolites as a chemical defence against fungivores. The toxicity of some of these fungal compounds have been tested against different invertebrates, however, it remains unknown whether grazers induce the anti-fungivore defence in moulds. In this thesis it is hypothesized that fungivory enhances the capacity of the fungi to kill or repel fungivores. The more resistant fungal phenotype is expected to show changes at the molecular genetic and biochemistry level. Specifically, changes at the expression levels of those genes related with the biosynthesis of secondary metabolites and changes at the fungal metabolic profile were expected. To test for an inducible anti-fungivore defence, Aspergillus nidulans was exposed to the grazing of Drosophila melanogaster larvae (Chapter 2). In this chapter it is shown that the grazing of the D. melanogaster larvae induces the anti-fungivore defence on the mould A. nidulans. The induction of the anti-fungivore defence is accompanied by a shift at the transcriptome level where the expression levels of some genes involved in the biosynthesis of secondary metabolites were up-regulated compare to their constitutive expression levels. In chapter 3 was investigated whether the variation in fungivore feeding damage induces different fungal responses. It has been previously suggested that the mechanisms underlying the anti-fungivore defence in the mould A. nidulans are suppressed by intense grazing. Therefore, in this chapter, it was hypothesized that the intense feeding damage produced by the isopod Oniscus asellus negatively affects the expression levels of those genes involved in the anti-fungivore defence of A. nidulans. Results of this chapter revealed that the intense grazing produced by the isopod down-regulates the anti-fungivore defence of the mould. Notably, different interactions in which fungi are engaged despite fungivory, may affect the anti-fungivore defence and therefore, the fungal capacity to harm fungivores. It is known that fungi compete chemically for resources and space against other microorganisms e.g. yeast. This chemical interference competition is commonly known as allelopathy and it is widespread between fungi e.g. mould and yeast. Yeast has the potential to release volatile organic compounds with antifungal activity that negatively affect mould growth. In chapter 4 it was hypothesized that yeast volatile organic compounds (VOCs) induce changes at the organismic, genetic and biochemistry level which influences the anti-fungivore defence of A. nidulans. A common response of moulds to microbial volatiles is a reduced production of conidiospores combined with a fluffy vegetative growth. This fluffy phenotype turned out to have modified levels of secondary metabolites, impaired capabilities to launch an induced defence response, which in combination leads to a significantly reduced capacity to resist fungivory. Results from this chapter show for the first time that fungal allelopathy affects the sign and strength of fungus-fungivore interactions. In conclusion, the results of this thesis demonstrates that fungivores have the capacity to enhance the anti-fungivore defence of the mould A. nidulans and thus affects the outcome of fungus-fungivore interactions. Moreover, the plasticity in the anti-fungivore defence is susceptible to variation in grazing intensity and chemically mediated intra-guild interactions. All these results indicate that the dynamics of fungus-fungivore interactions are more complex than thought and therefore further studies are required to determine the role of the inducible fungal defence in multi-species communities.
Keywords: fungal genetics; fungi; gene expression; grazing; insects; larvae; molds; secondary metabolism
