Gametocidal factor-induced structural rearrangements in rye chromosomes added to common wheat

The gametocidal factor on the Aegilops cylindrical chromosome 2C(c) was use d to induce and analyze the nature of chromosomal rearrangements in rye chr omosomes added to wheat. For this purpose we isolated plants disomic for a given rye chromosome and monosomic for 2C(c) and analyzed their progenies c ytologically. Rearranged rye chromosomes were identified in 7% of the proge nies and consisted of rye deficiencies (4.6%), wheat-rye dicentric and rye ring chromosomes (1.8%), and terminal translocations (0.6%). The dicentric and ring chromosomes initiated breakage-fusion-bridge cycles (BFB) that cea sed within a few weeks after germination as the result of chromosome healin g. Of 56 rye deficiencies identified, after backcrossing and selfing, only 33 were recovered in either homozygous or heterozygous condition covering a ll rye chromosomes except 7R. The low recovery rate is probably caused by t he presence of multiple rearrangements induced in the wheat genome that res ulted in poor plant vigor and seed set, low transmission, and an underestim ation of the frequency of wheat-rye dicentric chromosomes. Genomic in-situ hybridization (GISH) analysis of the 33 recovered rye deficiencies revealed that 30 resulted from a single break in one chromosome arm followed by the loss of the segment distal to the breakpoint. Only three had a wheat segme nt attached distal to the breakpoint. Although some of the Gc-induced rye r earrangements were derived from BFB cycles, all of the recovered rye rearra ngements were simple in structure. The healing of the broken chromosome end s was achieved either by the de-novo addition of telomeric repeats leading to deficiencies and telocentric chromosomes or by the fusion with other bro ken ends in the form of stable monocentric terminal translocation chromosom es.