rRNA gene expression and location in triticale assayed by silver staining and in situ hybridisation techniques

J. Lima-Brito

jbrito@utad.pt
Department of Genetics and Biotechnology, CGB/ICETA, University of Tras-os-Montes and Alto Douro, 5000-911 Vila Real, Portugal (Portugal)

A. Carvalho

Department of Genetics and Biotechnology, CGB/ICETA, University of Tras-os-Montes and Alto Douro, 5000-911 Vila Real, Portugal (Portugal)

C. Matos

Department of Genetics and Biotechnology, CGB/ICETA, University of Tras-os-Montes and Alto Douro, 5000-911 Vila Real, Portugal (Portugal)

Pat Heslop-Harriso

Department of Biology, University of Leicester, Leicester LE1 7RH, United Kingdom (United Kingdom)

H. Guedes-Pinto

Department of Genetics and Biotechnology, CGB/ICETA, University of Tras-os-Montes and Alto Douro, 5000-911 Vila Real, Portugal (Portugal)

Abstract

In durum wheat × rye hybrids and the derived amphiploid triticale, AABBRR, the expression of the 1R rRNA genes is largely suppressed. Alloauto-octoploid triticales, AABBRRRR, allows the evaluation if rye NOR inactivation can be overcome by the increase of rye genome number. In the present work, we used silver staining and in situ hybridisation techniques in order to study the nucleolar activity and to localize the rRNA genes in hexaploid and alloauto-octoploid triticales. The use of rye genomic DNA as probe allowed the identification of the rye chromosomes present in both hexaploid and octoploid triticales (14 and 28, respectively). The simultaneous use of the ribosomal sequence enabled the localisation of 18S-25S rDNA on the satellite chromosomes of both triticales. On hexaploid triticale we detected six rDNA sites (four on wheat chromosome pairs 1B and 6B and two on rye chromosome pair 1R), whereas on alloauto-octoploid triticale eight rDNA sites (four on wheat-pairs 1B and 6B and four on rye chromosome pairs 1R) were observed. As expected, the maximum number of active Ag-NORs per metaphase cell was coincident with the maximum number of nucleoli per interphase nucleus confirming that all and only the NORs functionally active during interphase are stained by silver at the next mitotic metaphase. Comparison of the nucleolar activity between hexaploid and octoploid triticales analysed here indicates that the increase in 1R chromosomes from two to four does not change the suppression of rye nucleolar activity. This supports the suggestion that genomic interactions are under strong genetic control.

Keywords:

amphiploids, in situ hybridisation, nucleolar dominance, rDNA, silver staining, triticale