Diptericin as a model for understanding the specificity of host-pathogen interactions
A polymorphism at a single residue in the diptericin glycine-rich domain drastically affects its activity against the Gram-negative bacterium Providencia rettgeri . [6] Flies with a Diptericin A gene encoding a serine allele survive infection significantly more than flies with an arginine allele. It is unclear how frequently such polymorphisms may dictate host-pathogen interactions, but there is evidence of widespread balancing selection that diptericin is not the only AMP with such polymorphisms. [7] [8] This close association between diptericin and P. rettgeri is further supported by genetic approaches that show that diptericin is the only antimicrobial peptide of the Drosophila immune response that affects resistance to P. rettgeri. [9]
The fruit fly Diptericin gene "Diptericin B" has a unique structure that has been derived independently in both Tephritidae and Drosophila fruit flies. This represents convergent evolution of an antimicrobial peptide towards a common structure in two separate fruit-feeding lineages. This convergent evolution is driven by presence of Acetobacter bacteria in fruit-feeding ecologies. [10] Absence of Acetobacter in other ecologies has led to subsequent loss of Diptericin B. [10] [11] Diptericin B loss is also convergent among lineages feeding on mushrooms or plants, including the mushroom-feeding fruit flies Leucophenga varia , Drosophila guttifera and Drosophila testacea , and plant-feeding Scaptomyza flies. [10]
These observations are part of a growing body of evidence that antimicrobial peptides can have intimate associations with microbes, and perhaps host ecology, in contrast to the previous philosophy that these peptides act in generalist and redundant fashions. [7] [11] [12] [13]
