SOYBEAN CHROMOSOME PAINTING - A STRATEGY FOR SOMATIC CYTOGENETICS

Cytological identification of soybean mitotic metaphase chromosomes (2 n = 40) has been severely limited by their small size and uniform kary omorphology, We have developed fluorescent in situ hybridization (FISH ), PCR-primed in situ labeling (PCR-PRINS) procedures, and molecular p robes for routine cytological identification and for the physical mapp ing of soybean somatic chromosomes, Chromosome preparation has been ac hieved by modifications of previous protocols and through the preparat ion of root-tip protoplasts prior to chromosome spreading, Initially o ur probe selection focused on highly repeated DNAs that provide very i ntense localized hybridization signals, Repetitive gene probes that ha ve proven valuable include the rDNA loci (55 and 45S) which are chromo some specific, We have also developed satellite DNA probes for two dif ferent sequence families: the SB92 and the STR120 satellites, Both of these are tandemly arranged at multiple chromosomal loci, By using dif ferent cloned examples of each family, we have been able to selectivel y label unique subsets of soybean chromosomes, Double hybridization wi th biotin and digoxigenin labeled probes has allowed us to determine t he chromosomal overlap between different probes, In addition, we have joined portions of the metaphase chromosome painting patterns with the genetic map by single-copy FISH and PCR-PRINS detection of the RFLP l oci G8.15, G17.3, and A199a and A199b, Total genomic DNA in situ hybri dization (GISH) patterns were also used to characterize the soybean ch romosomes.