PROJECT SUMMARY/ABSTRACT
The co-evolution of bacterial protein toxins and their targets has led to the discovery of many novel protein
modifications and the development of applications in molecular biology. Arthropods, the most diverse phylum
on Earth, are hosts to many bacterial symbionts that secrete diverse toxins of unknown function during
infection. The maternally transmitted, intracellular parasite Spiroplasma poulsonii encodes one such toxin
(Spiroplasma androcidin or Spaid) that causes male killing in its natural host Drosophila melanogaster. This
proposed project aims to understand how the bacterial toxin Spaid recognizes the host cellular environment to
specifically kill males. To that end, we use the Spiroplasma-Drosophila model system and a combination of
genetics and molecular biology to identify specific host proteins targeted by Spaid and how the toxin binds
these proteins.
Previous work has suggested that Spiroplasma, via Spaid, detects the presence of the male specific lethal
complex in flies. This complex is responsible for dosage compensation in male flies, which lack a second copy
of the X. It is formed during early development in males and is part of the Drosophila sex determination
pathway. Given this result, we hypothesized that natural resistance to Spaid would exist in Drosophila
populations, that the target of Spaid is part of the dosage compensation complex (dcc), and that Spaid directly
binds to dcc components, altering their activity. Our strong preliminary data suggest that we are correct, as we
find natural variants of Drosophila melanogaster (within the DGRP), which produce males in the presence of
Spaid and/or Spiroplasma. We also find that tissue specific knockdown of dcc components partially suppresses
Spaid toxicity in male tissue.
Towards this hypothesis, and guided by strong preliminary data, we propose to pursue two Specific Aims to
identify host proteins that interact directly with the Spaid toxin and characterize how variation within host
proteins and Spaid affect male killing at the molecular and cellular level. We will (1) Identify Spaid targets using
a yeast 2-hybrid screen and co-immunoprecipitation, (2) identify suppressors of Spaid toxicity using natural
variation in Drosophila and a genetic screen.
Results from these experiments will illustrate how a bacterial toxin manipulates the host cellular environment.