Abstract
Understanding how microorganisms and their hosts
interact at different biological levels (e.g. genetic, cellular,
ecological and population) is of fundamental importance. We will
address this question using a widespread and important group of
intracellular bacteria called Wolbachia. Wolbachia occurs in up to 70%
of insect species and its spread represents one of the great pandemics
of life on this planet. They have broad effects on their hosts, ranging
from sperm-egg incompatibility to feminization, male-killing and
induction of parthenogenesis. We will conduct a set of integrated
studies to investigate Wolbachia-host interactions. A team with
expertise in genomics, genetics, molecular biology, population biology,
ecology and systematics have been assembled to achieve this goal. Our
studies will determine the genomic diversity of Wolbachia, genetic
changes associated with host shifts, extent of gene transfer from
Wolbachia to hosts, and the patterns of movement of Wolbachia globally
and within insect communities. These biodiversity investigations will
be combined with studies of the mechanisms by which Wolbachia induce
reproductive alterations in their hosts, and the genetic, molecular and
population basis of host modifications of Wolbachia. Finally, we will
investigate the long-term consequences of infection, including the
potential role of Wolbachia in host speciation. Broader implications of
this project include enhancing understanding of the mechanisms by which
parasites manipulate fundamental cellular processes in their hosts,
interactions of bacterial and host genomes, and the role Wolbachia may
have played in the spectacular diversification of insects. Furthermore,
Wolbachia could be an effective means for biological control of insect
pests and vectors of disease. Our program, by addressing key questions
on the effects of Wolbachia on insect genomes, species and communities,
will give trainees from high school to postdoctoral levels exposure to
both the methods and perspective of an interdisciplinary approach to
science. These trainees, therefore, will be well equipped to explore
important biological questions from an integrative perspective. Because
Wolbachia have such dramatic effects, they have attracted considerable
public interest. Research resulting from this project therefore will be
effective as a means of broadly promoting science education.
Objectives
We propose a research program involving genomic,
functional, ecological, and evolutionary approaches to investigate
interactions between Wolbachia and insects. We will focus on the
following key questions. (1) How variable are Wolbachia genomes and
what genetic changes are associated with shifts to new hosts or
phenotypes?, (2) What are the cellular and genetic mechanisms of
Wolbachia-host interactions (i.e. how do Wolbachia alter host
reproduction and hosts modify Wolbachia expression and transmission)?,
(3) How are Wolbachia distributed and how do they move within arthropod
communities?, and (4) What are the evolutionary consequences of
Wolbachia infection?
Our approach is to break each question down into
sets of testable hypotheses, and then integrate the results across
studies to gain a broader understanding of how Wolbachia affect insect
function, ecology and evolution. This involves coordinating research
across broad biological disciplines. For this purpose we have assembled
an outstanding team of collaborators, including individuals with
expertise in genomics and bioinformatics (Tettelin, Pearce, Ogihara,
White), molecular biology and genetics (Sullivan, Karr, Tram, Werren),
insect ecology and systematics (DeSalle, Heraty, Jaenike, Windsor),
evolutionary biology (Hayashi, Jaenike, Stouthamer, Werren) and
microbial symbiosis (Bordenstein, Stouthamer, Wernegren, Werren), as
well as additional collaborators who will assist in various aspects of
the project (Bourtzis, Brower, Eisen, Godfray, Hammerstein,
O’Grady). The objectives and integration of research effort are
briefly summarized below.
1. Genomics: Our basic objectives are to
characterize the genomic diversity of Wolbachia and to use this
information to investigate ecological, functional and evolutionary
questions. Using genomic approaches, we will determine (a) the baseline
genomic diversity of Wolbachia, (b) what genetic changes occur
following shifts to new hosts or phenotypes (e.g. CI, MK, PI), and (c)
the extent to which Wolbachia genes have been transferred to eukaryotic
host genomes. We have the requisite expertise in microbial genomics and
genetics for this research, which takes advantage of the full genome
sequence produced for one Wolbachia strain at TIGR, and additional
Wolbachia genome sequences being produced by our collaborators
(Bourtzis). The genomic research provides baseline information on
Wolbachia genome diversity that is required for our ecological and
evolutionary studies, as well as important tools (e.g. microarrays) and
data for functional studies of Wolbachia.
2. Function: Our primary objectives are to (a) investigate the mechanisms of action of CI, MK, and PI
Wolbachia, (b) determine how infections change
host gene expression and (c) determine how host genotypes modify
Wolbachia expression and transmission. A combination of molecular
cytological, protein, and microarray approaches will be used to
investigate mechanisms of action of CI, MK and PI Wolbachia. The
studies build on previous work and will test specific hypotheses
regarding modes of action. The second aspect of functional studies is
geared towards identifying genes involved in host-Wolbachia interaction
using host genotypes known to modify Wolbachia, and others emerging
from the ecological and evolutionary studies. Understanding Wolbachia
intracellular function provides a key link between the genomic/genetic
basis of Wolbachia action and the evolutionary/ecological effects of
Wolbachia infections.
3. Ecology: Our basic objectives are to
investigate the patterns and mechanisms of movement of Wolbachia
through arthropod communities, and to identify for further study
Wolbachia strains that have undergone rapid host range expansion or
changes in phenotypic effects on hosts. We have assembled an
outstanding team to conduct a much more systematic sampling, which will
permit testing of a variety of ecological hypotheses. There will be
three components to the sampling program, (a) geographic, (b)
community, and (c) taxon-focused. Arthropods will be sampled from
specific geographic regions on each of the major continents along
latitudinal and longitudinal transects, to determine global patterns of
diversity and movement of Wolbachia. Second, a set of
well-characterized arthropod communities will be intensively sampled to
infer patterns of movement of sample a set of insect taxa for which
well-developed phylogenies are available are tractable for laboratory
study. This will permit us to overlay onto host phylogenies and for
studies of host-research are used in genomic, functional and
evolutionary projects.
4. Evolution: Our primary goal here infection. We
will address four specific issues (a) evolution of modifiers and
natural populations, (b) rates of evolution of host genes (particularly
those a consequence of infection, (c) the evolutionary fate of effects
of Wolbachia resources for genomic and functional projects, and allow
us to evaluate the insect evolution.
Integration of Research and Training
Integration of the research components is
elaborated upon in the research plan key features. Genomic research
provides information on genomic resources thus generated are utilized
in the functional, ecological, Functional research targets cellular
mechanisms of action of expression and transmission, and identifies
candidate host genes for Ecological studies identify bacterial-host
systems for more detailed functional, studies, and places host genetic
modifiers of and Wolbachia genomes, the various components of research
are integrated in a highly networked rather Special efforts are taken
to integrate research and education components individuals in different
laboratories, training courses for participating students, and PI and
collaborator participation in thesis advising. As a result, cemented by
a flow of information, resources and personnel between the laboratories.
We are proposing an ambitious research program
feasibility. Additional factors relevant to evaluating feasibility are
(a) expertise assembled team, (b) prior record of collaboration, (c)
leveraging of resources, We have assembled an outstanding team with
expertise in each of the major functional biology (molecular,
development and genetics), ecology (both evolution. Furthermore, many
members of our team have an extensive history productivity, as
evidenced by collaborative publications (for example projects
(described below). Collaborative publications are indicated by * in and
past collaborations reflect our ability to work together to accomplish
There is an extensive leveraging of research effort our goals
practical. This is discussed in more detail under Management Plan;
presented here. The ambitious ecological sampling scheme is made
feasible collection, identification, archiving and storage network
available through the Natural History (DeSalle), Smithsonian
Institution (Windsor), and (Godfray). As a result, the systematic
sampling program described here is because many of the collections will
be accomplished through ongoing efforts examples of resource leveraging
are with Bordenstein, who is independently Wolbachia , with White who
has conducted theoretical studies (see relevant Letters).
In addition, many projects are supported by the
proposed research. These include molecular cytology of CI (Tram) and
Nasonia, preliminary studies of on genetic modifiers of methods in
symbiotic bacteria (Tettelin). General feasibility of this project is
collegial nature of the resources by members of the community (letters
Brower, Dobson, Godfray, Hoffmann, White).
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