Common Toolbox Based On Necrotrophy In A Fungal Lineage

One of the most exciting aspects of the genomic revolution in biology is understanding the genetic mechanisms behind an organisms natural history.  Within the fungi it has been fascinating to begin to tease apart how seemingly similar life histories can be explained by disparate genomic landscapes, or opposingly, how completely different modes of survival can be explained by a common set of genes.  There has been a steady increase in research over the last few years documenting a large array of tools in the genomic toolbox.

A recently published paper in the journal PLOS One, authored by Andrew et al., entitled “Evidence for a Common Toolbox Based on Necrotrophy in a Fungal Lineage Spanning Necrotrophs, Biotrophs, Endophytes, Host Generalists and Specialists” comes from the Kohn Lab at the University of Toronto, which has long studied the fungal family Sclerotiniaceae.  The Sclerotiniaceae is a group of Ascomycetes known for being typically necrotic pathogens which are host generalists or specialists.

This is a great group of fungi to address questions like: why is one species necrotic while another is just biotrophic? …and why are some fungi specialists, while others generally infect plants without regard to taxonomy?  To address these questions the authors sampled across 52 strains of fungi in the Sclerotiniaceae representing 30 taxa covering the spectrum of host specificity/generality and trophic types.  They chose a suite of genes responsible for both general cell housekeeping (controls, etc.) and associated with pathogenicity and constructed phylogenies of these genes to observe relationships between these 52 strains.  Evidence of positive selection acting on these genes, as well as site-specific selection, was also assessed.  Lastly, the authors assessed the pathogenicity of these strains by initiating infection studies on Arabidopsis thaliana plants.

The authors found that there are at least two origins of biotrophy from a necrotrophic ancestor in the Sclerotiniaceae and that there is evidence of selection on all the genes associated with pathogenicity tested in this study.  The housekeeping genes in this study were used to control for the phylogenetic analysis and showed no evidence of positive selection as opposed to the pathogenicity genes.  Furthermore, likelihood analyses showed no statistical differences in the genes of strains from different trophic lifestyles, as well as host generalists and specialists.

Within this study on the Sclerotiniaceae, it appears that there is a common tool box of genes shared by the fungal strains studied here.  The level of expression of genes differed in this study, which could explain trophic and host specificity differences exhibited by these fungi.  It will be interesting when we have more genome sequences from this family to see how genome structure and rearrangements have contributed to the expression and diversity of genes associated with necrotrophy in this family of fungi.