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Uncovering molecular mechanisms of pathogenicity in the banana pathogen Fusarium oxysporum f.sp. cubense

Elizabeth Czislowski: School of Agriculture and Food Sciences, The University of Queensland

<div>Banana is an incredibly important crop due to its value as a subsistence crop for millions of people throughout the world as well as its value as an export commodity for many countries. The ongoing cultivation of banana in all growing regions is under threat from the hypervirulent Tropical Race 4 (TR4) variant of the fungal pathogen, <em>Fusarium oxysporum </em>f.sp.<em> cubense </em>(<em>Foc</em>)<em>. </em>Currently, it is hypothesised that the host-specific pathogenicity of fungal pathogens is influenced by small, secreted proteins termed effectors. This study sought to understand the repertoire of effector genes present in lineages of <em>Foc </em>and how these genes have influenced the evolution of this pathogen. Using a systematics approach, we investigated the distribution and diversity of a family of fungal effectors named the <em><strong>s</strong></em><em>ecreted <strong>i</strong>n <strong>x</strong>ylem </em>(<em>SIX</em>) genes in the different genetic lineages of <em>Foc</em>. We identified homologues of several <em>SIX </em>genes that were specifically associated with the TR4 lineage of <em>Foc</em>. Sampling of <em>Fusarium spp.</em> associated with asymptomatic bananas also revealed that endophytic isolates of <em>F. oxysporum</em><em>,</em><em> </em>and interestingly other <em>Fusarium spp.</em><em>,</em><em> </em>carried several <em>SIX </em>genes. Hypothesis testing indicated that the <em>SIX </em>genes in banana-infecting isolates of <em>F. oxysporum </em>had been acquired through horizontal gene transfer events. To investigate this further, we have undertaken a comparative genomics approach using TR4 and two less pathogenic lineages to identify regions of the <em>Foc </em>genome implicated in pathogenicity. This study has important implications for understanding the molecular mechanisms of pathogenicity in <em>Foc </em>and more specifically the molecular factors that confer the hypervirulence of TR4.</div>