THE 5S-DNA UNITS OF BREAD WHEAT (TRITICUM-AESTIVUM)

A collection of 44 cloned 5S DNA units from Triticum aestivum cv. 'Chinese Spring' were grouped into 12 sequence-types based on sequence similarity and the respective consensus sequences were then produced. The relationship between these 12 consensus sequences (T. aestivum S1-S8 and T. aestivum L1-L4), together with two clones sequenced by GERLACH and DYER, and the 5S DNA consensus sequences from diploid Triticum spp. were then determined by numerical methods. Both phenetic and cladistic analyses were carried out. The following wheat 5S DNA sequences were found to group with respective sequences from diploid Triticum spp.: T. aestivum S4, S6 with T. tauschii S; T. aestivum S3 with T. monococcum S and T. monococcum S-Rus 7; T. aestivum L1 and T. aestivum L-G&D with T. speltoides L; T. aestivum L2, L3 with T. tauschii L; T. aestivum L4 with T. monococcum L and T. monococcum L-Rus 12. The analyses suggested that 5 out of the 6 5S Dna loci present in wheat were identified at the sequence level. The locus that could not be identified in this analysis was the 5S Dna-B1 locus. A group of T. aestivum sequences (T. aestivum S1, S7, S8, S-G&D) were found to be distinct from the other 5S DNA sequences in the data base. The existence of the distinct group of 5S DNA sequences suggests that there is a gap in our current understanding of wheat evolution with respect to the 5S Dna loci.