Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 81pg1
MOLECULAR ANALYSIS OF HOMOLOGOUS REGIONS OF THE
SOYBEAN GENOME FOR HOMEOLOGY AND REPEATED SEQUENCES.
K. M. Polzin 1, E. Calvo 2, and R. C. Shoemaker 1, 1
USDA/ARS/FCR and 2 Dept. of Zoology/Genetics, Iowa State
University, Ames, IA 50011.
The modern soybean genome is thought to have been derived by
tetraploidization followed by chromosome rearrangements resulting
in diploidization. Such events should result in the presence of
large and/or small homeologous regions depending on the level of
'scrambling' during diploidization. We have analyzed genomic
clones (12-16 kb) of the soybean genome that contain sequences
homologous either to pA071, a random genomic Pstl fragment, or
pSle, a cDNA of a soybean seed-specific late embryogenic gene, by
restriction mapping and cross hybridization for evidence of
homeology. Seven pA071- and three pSle-hybridizing regions 11
were assayed. A pair of potentially homeologous clones was
identified for each probe. In both cases, a region of >8 kb
surrounding the probe hybridizing region showed cross
hybridization at high stringency (O.1X SSC, 60C) and conservation
of restriction sites, followed by regions which did not cross
hybridize even at low stringency (0.5X SSC, 60C) and which showed
little or no conservation of restriction sites. The extent of
the homologous regions could not be determined since the homology
extended to the end of the clone. The remaining clones showed
homology only in the probe-hybridizing region suggesting either
extensive divergence between homeologs and/or that these clones
correspond to other copies of the probe sequences present at
different sites in the tetraploid. Since not all
pA071-hybridizing fragments of the soybean genome were recovered
as EMBL3 clones, the failure to find homeologous partners for the
remaining five unpaired pA071 EMBL3 clones may be due to the
homeologs being among the uncloned fragments or to the homeologs
for these clones having been deleted during diploidization. To
further elucidate the structure of the soybean genome we have
also analyzed some of the above clones for repeated sequences.
Our results show that these regions contain primarily low and
middle-repetitive sequences (10-20, and >20 but distinct bands,
respectively).
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