Plant & Animal Genome VI Conference Plant & Animal Genome VI Conference
S13
University of Georgia, Depts. of Genetics/Botany, Life Sciences Bldg., Athens, GA 30602
Miniature inverted repeat transposable elements (MITEs) have
been found to be frequently associated with the non-coding
regions of genes from a variety of plant species including
maize, rice, and tomato, and from non-plant species including
some insects, mammals and worms. In several instances
MITEs provide regulatory sequences including the
sites for transcription initiation and polyadenylation.
Despite their important role in shaping plant genomes, their
mode of transposition remains a mystery since all MITEs
isolated to date have no coding capacity and are classified
as non-autonomous. Since their structure is reminiscent of
DNA elements, especially the Ds1 class of maize, our
working hypothesis is that they are DNA elements that
have managed to attain incredibly high copy numbers.
To understand how MITEs transpose and contribute to
genetic diversity, we have focused on several families of
maize MITEs that may still be capable of transposition.
One family, called heartbreaker (Hbr) was originally isolated
as an insertion into the disease resistance gene HM1.
Characterization of about 50 of the 2000 copies of Hbr elements
in the genome reveals greater than 90% sequence conservation
and length uniformity. Preliminary results indicate that
insertion sites are generally low or single copy sequences
and that these sites are remarkably polymorphic for the
presence or absence of elements among the maize and teosinte
strains surveyed. Other distinct element families have been
identified in the maize genome with properties very similar
to the Hbr family. These data are consistent with a recent
and massive amplification of Hbr and other MITE families
in the maize genome.