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Description
Telomeres are specialized DNA sequences that form the ends of eukaryotic chromosomes and
are required to prevent the progressive loss of terminal DNA sequences during chromosome
replication. In most eukaryotes, the telomeres consist of tandem arrays of simple sequence
repeats; and the end-maintenance problem is solved by the periodic addition of new repeats to
existing ends by telomerase, a specialized reverse transcriptase. Some eukaryotes lack
telomerase and have different strategies for solving the end replication problem. The
best-studied example is Drosophila, whose telomeres consist of the retrotransposons TART and
HeT-A, which also are added to chromosome ends via reverse transcription. In addition to
protecting chromosome ends, telomeres are involved in chromosome pairing and movement, can
silence neighboring genes and are highly plastic. My laboratory is studying telomere plasticity
in the plant-pathogenic fungus Magnaporthe oryzae, as this has been associated with pathogenic
variability. M oryzae isolates that infect perennial ryegrass have unusually unstable telomeres
that undergo continual rearrangements both in culture and in planta. By comparison, telomeres
in most other host-specific forms of this fungus are quite stable. Sequencing revealed that the
chromosome ends of the ryegrass pathogens are organized very differently to those in a strain
with stable telomeres. Specifically, the ryegrass pathogen telomeres contain tandem arrays of
retrotransposon-like sequences separated by short TTAGGG motifs. The arrays are capped at
the chromosome end by a "normal" telomere sequence, which in M oryzae is (TT AGGG)n. This
arrangement is reminiscent of the TRAS and SART retrotransposons, which insert into telomeres
in the silkworm, Bombyx mori. However, the M oryzae elements, which we call MoTERs (for
M oryzae telomere-exclusive repeats), are organized quite differently to TRAS and SARI.
Most importantly, they lack the endonuclease gene required for insertion into DNA. Instead, the
particular organization of MoTERs at the chromosome ends suggests they are added on to the
ends of chromosomes in the same manner as TART and HeT-A in Drosophila. These
observations lead me to hypothesize that telomere instability in M oryzae is due to the activities
of two telomere maintenance mechanisms - one utilizing telomerase to extend TT AGGG repeats,
and the other involving retrotransposition of MoTERs sequences onto free DNA ends that result
from end-degradation. The goal of the proposed experiments is to test this hypothesis and
develop resources for future mechanistic studies. The specific aims are: 1) To determine the
molecular basis for telomere instability. 2) Knock-out the telomerase gene to assess the roles of
telomerase and MoTERs in telomere maintenance; and 3) To study the genetics of MoTER
transposition.
Status | Finished |
---|---|
Effective start/end date | 4/1/07 → 3/31/12 |
Funding
- National Science Foundation: $354,872.00
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Projects
- 2 Finished
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REU: Telomere Hypervariability in the Fungus, Magnaporthe Oryzae - A Model Plant Pathogen
5/16/11 → 3/31/12
Project: Research project
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Telomere Hypervariability in the Fungus, Magnaporthe Oryzae - A Model Plant Pathogen
4/1/07 → 3/31/12
Project: Research project