NUCLEOLAR DOMINANCE IN TRITICALES - CONTROL BY UNLINKED GENES

Hybrid plants and animals often show suppression of activity of riboso mal genes (rDNA) originating from one of the parental or ancestral spe cies. wheat x rye amphiploid triticale, chromosomes of wheat origin an d 14 from rye, rDNA of rye origin (on chromosome 1R) is not normally e xpressed, while the 1B- and GB-origin rDNA from wheat shows strong exp ression. Expression of rDNA can be accurately assessed by the silver s taining method, which stains both interphase nucleoli and metaphase rD NA sites that were actively expressed at the previous interphase. We s how here that substitution of another rye chromosome, 2R, by a chromos ome from hexaploid wheat, 2D (triticale-PD(PR)), prevents suppression of the rye-origin rDNA, and leads to activity of all six major rDNA lo ci. These results were found in two different triticales and supported by rDNA behaviour in wheat-rye chromosomal addition lines. Models for chromosomal interactions leading to control of rDNA expression are pr esented.