Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 9pg1
COMBINED MAPPING AND SEQUENCING OF RANDOMLY-SELECTED cDNAS IN
MAIZE.
Tim Helentjaris, Tom McCreery, and Ivone Torres-Jerez, Department
of Plant Sciences, University of Arizona, Tucson, AZ 85721.
In order to utilize genomic data in maize as a tool to
isolate sequences for genes of interest but also avoid the
problems associated with large genomes, a map-based cloning
strategy is being explored as an alternative to
chromosome-walking. Given the extremely high polymorphism rates
in maize, it is comparatively easy to map >90% of
randomly-selected clones within publicly available recombinant
inbred populations. Using cDNA clones as the target pool reduces
the problem of repetitive sequences, yields mapping data on
sequences of direct interest, but introduces the complication of
abundant mRNAs. By combining this approach with that of
sequencing in from the 5' end of every cDNA that is mapped,
very large numbers of expressed sequences can be assigned genomic
origins, many will be identified through homologies with known
motifs, and the maize map will be correlated with every other
species (such as arabidopsis and rice) with large-scale
sequencing programs. If it proves practical to map and
characterize very large numbers of expressed sequences, this
strategy in itself might effectively circumvent the aspect of
traversing long segments of genomic DNA to isolate genic
sequences of interest defined primarily by their genomic
location. In an initial test case of this idea, approximately
200 randomly-selected maize seed cDNA clones were both mapped and
sequenced. Seed genes were targeted as there are many mapped
seed mutants and it was hoped that this would enhance
opportunities to correlate cloned sequences with mapped mutants.
Abundant sequences proved somewhat problematical as expected but
putative correlations by both sequencing and mapping were
observed. The results will be discussed in terms of future
opportunities for this global approach, as well as modifications
for targeting specific genes.
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