Functionality of major and minor 45S rDNA sites in different diploid wild species and varieties of sunflowers

Abstract

Abstract The genus Helianthus includes diploid (2n = 2x = 34), tetraploid (2n = 4x = 68) and hexaploid (2n = 6x = 102) species, and genome evolution based on extensive diversity due to free hybridization, introgression and polyploidy. The wild diploid species H. debilis, H. praecox and H. nuttallii showed 2n=34 with four 45S rDNA sites. The cultivated sunflower (H. annuus), also diploid, showed six and eight 45S rDNA sites, being six major and two minor terminal rDNA sites. Samples were studied using C-CMA3 and NOR banding to determinate the functionality of minor 45S rDNA sites. Additionally, FISH with 45S and 5S rDNA probes were performed. Results showed that the number and the position of 45S and 5S rDNA sites maintenance in cultivated karyotypes, but provide evidence of a possible increasing in number of rDNA 45S sites when compared with the wild diploid species. Besides, results of C-CMA3 and NOR banding showed that the minor sites are not associated with GC-rich heterochromatin but, even thus, are f...