The fate of ribosomal genes in three interspecific somatic hybrids of Medicago sativa: three different outcomes including the rapid amplification of new spacer-length variants

• Published in: Theoretical and applied genetics Vol. 93; no. 5-6; pp. 801 - 808
• Main Authors: Cluster, P.D, Calderini, O, Pupilli, F, Crea, F, Damiani, F, Arcioni, S. (Consiglio Nazionale delle Ricerche, Perugia (Italy). Ist. di Ricerche sul Miglioramento Genetico della Piante Foraggere)
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01-10-1996; Berlin
• Subjects: Biological and medical sciences; Classical genetics, quantitative genetics, hybrids; Fundamental and applied biological sciences. Psychology; GENE; GENES; GENETIC VARIATION; Genetics of eukaryotes. Biological and molecular evolution; HIBRIDOS SOMATICOS; HYBRIDE SOMATIQUE; MEDICAGO SATIVA; Pteridophyta, spermatophyta; RIBOSOMAS; RIBOSOME; RIBOSOMES; SOMATIC HYBRIDS; SOMATIC VARIATION; VARIACION GENETICA; VARIACION SOMATICA; VARIATION GENETIQUE; VARIATION SOMATIQUE; Vegetals; Genetic marker; Ribosomal DNA; Medicago sativa; Spacer DNA; 18S-RNA; Somaclonal variation; Nonhomologous recombination; Restriction fragment length polymorphism; Leguminosae; Dicotyledones; Angiospermae; Interspecific hybridization; Somatic hybrid; Spermatophyta; Fodder crop
• ISSN: 0040-5752; 1432-2242
• DOI: 10.1007/BF00224079

We have characterized the genetic consequences of somatic hybridization within the ribosomal DNA (rDNA) of three interspecific hybrids, each involving M. sativa as one of the parents. Restriction-fragment-length-polymorphisms (RFLPs) of rDNA spacers and fluorescent-in-situ-hybridization (FISH) of an 18S-gene probe to mitotic chromosomes were used to compare parental and hybrid species. The M. sativa-coerulea hybrid retained all six parental nucleolar-organizing regions (NORs) and all parental RFLPs representing a complete integration of rDNA. The M. sativa-arborea hybrid retained five of six parental NORs while losing half of the arborea-specific RFLPs, indicating that simple chromosome loss of one arborea NOR accounted for the RFLP losses. Dramatic alterations occurred within the M. sativa-falcata hybrid where five of six parental NORs were retained and new rDNA RFLPs were created and amplified differentially among somaclonal-variant plants. The molecular basis of the new RFLPs involved increased numbers of a 340-bp subrepeating element within the rDNA intergenic spacer (IGS), suggesting that recurrent cycles of unequal recombination occurred at high frequency within the rDNA in somatic lineages.