Davidjuk Y. Variability of plant rDNA and its using as the molecular marker

Molecular organization and variability of ribosomal DNA (rDNA) and its inheritance in hybrids were studied in Zea mais and in several Narcissus and Nicotiana species. In maize, a moderate length and sequence heterogeneity was found in intergenic spacer region (IGS) of rDNA. Ribosomal DNA variants characteristic for both parental forms were detected in sexual hybrids demonstrating that in maize rDNA remains unaltered after hybridization. Therefore, the structural features of rDNA may be used for molecular identification of breading lines, varieties and hybrids of maize. A significant length and sequence heterogeneity of IGS was revealed in genus Narcissus applying rDNA restriction mapping. Respectively, rDNA represents a proper molecular marker for identification of parental species of modern vegetatively propagated cultivars of Narcissus x hybridus hort. In the Nicotiana species studied intragenomic length homogeneity of rDNA was observed. Each of the species can be discriminated according to the presence/absence or localization of certain restriction sites in the IGS. Suitability of rDNA as a marker for the molecular phylogeny reconstruction in the genus Nicotiana was demonstrated. The 5' external transcribed spacer (ETS) of rDNA of Nicotiana paniculata was cloned, sequenced and compared with the 5' ETS sequence data available for other Nicotiana species. A scheme reflecting amplification of A-subrepeats during molecular evolution of the 5' ETS of N. paniculata was proposed.