Opening Pandora's Box: Toward an Anti-Fungal Defense Mechanism Open Access

Abstract

The study of host-pathogen interactions has been a central focus of both ecological and evolutionary research. The discovery of diverse bacterial communities in many animals, including humans, has spurred new research into the interactions between host, pathogens and beneficial microbes. Here I present new insights into the relationship between a fungal pathogen, Pandora neoaphidis, its insect host, Acyrthosiphon pisum, and a facultative, defensive, bacterial aphid symbiont, Regiella insectola. The Regiella bacterium has been shown to confer protection onto its host against a variety of pathogen and predators including the Pandora fungus and parasitoid wasps. Specific mechanisms of action in this defense are currently unknown. The Pandora fungus is often cited as a potential bio control mechanism for aphid agricultural infestations; however, there are few genomic resources available for the study of Pandora infections. Using next generation RNA sequencing reads, I assembled a draft de novo transcriptome of Pandora during an infection. I then examined the differential transcript expression of the fungus in the absence and presense of the protective symbiont as well as in unwinged and winged aphid morphs, which differ in their susceptibility to fungal pathogens as well. The presence of the protective symbiont led to the decrease in the expression of Pandora transcripts containing domains associated with pathogenesis and fungal proliferation suggesting that the bacterium interferes with these processes. Differential expression of transcripts associated with fungal growth, stress response, and sporulation was noted between Pandora infections of winged aphids and those of unwinged aphids. It has been demonstrated that the production of winged morphology results in an energy deficit that decreases the efficacy of an immune response. These findings suggest that unwinged individuals are better able to suppress the production of fungal genetic elements involved in the destructive processes of fungal growth and sporulation. This leads to a lowering in mortality and less fungal dispersion after death. Future research will be required to investigate the specifics of these infection mechanisms.

Table of Contents

CHAPTER I: Introduction ........................................................... 1

CHAPTER II ............................................................................. 10

Table 1 ................................................................................... 13

Figure 1 .................................................................................. 15

Figure 2 .................................................................................. 16

Table 2 ................................................................................... 17

Table 3 ................................................................................... 18

CHAPTER III ............................................................................ 22

Table 1 ................................................................................... 24

Figure 1 .................................................................................. 27

Table 2 ................................................................................... 28

Table 3 ................................................................................... 29

Table 4 . .................................................................................. 29

Table 5. ................................................................................... 30

Table 6 ................................................................................... 30

CHAPTER IV ............................................................................ 36

Table 1 ................................................................................... 38

Figure 1 .................................................................................. 41

Table 2 . .................................................................................. 42

Table 3 . .................................................................................. 43

Table 4 ................................................................................... 43

CHAPTER V: Conclusions ........................................................... 47

Table 1 ................................................................................... 49

References .............................................................................. 50

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	BS
Submission	Honors Thesis
Language	English
Research Field	Biology, Genetics Biology, Bioinformatics Biology, Ecology
Keyword	Fungal Pathogen Host-Pathogen Interaction Transcriptomics Symbiotic Bacteria
Committee Chair / Thesis Advisor	Gerardo, Nicole Marie, Emory University
Committee Members	Read, Timothy D, Emory University Morran, Levi T, Emory University

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