title: New 18S.26S ribosomal RNA gene loci: chromosomal landmarks for the evolution of polyploid wheats.
abstract: Three new 18S.26S rRNA gene loci were identified in common wheat by sequential N-banding and in situ hybridization (ISH) analysis. Locus Nor-A7 is located at the terminal area of the long arm of 5A in both diploid and polyploid wheats. Locus Nor-B6 is located in N-band 1BL2.5 of the long arm of chromosome 1B in Triticum turgidum and Triticum aestivum. ISH sites, similar to Nor-B6, were also detected on the long arms of chromosomes 1G in Triticum timopheevii and 1S in Aegilops speltoides, but their locations on the chromosomes were different from that of Nor-B6, indicating possible chromosome rearrangements in 1GL and 1BL during evolution. The third new locus, Nor-D8, was only found on the short arm of chromosome 3D in the common wheat Wichita. The loss of rRNA gene locus Nor-A3 and gain of repetitive DNA sequence pSc119 on the terminal part of 5AS suggest a structural modification of 5AS. Comparative studies of the location of the 18S.26S rRNA gene loci in polyploid wheats and putative A and B (G) genome progenitor species support the idea that: (1) Triticum monococcum subsp. urartu is the donor of both the A and A(t) genome of polyploid wheats. (2) Ae. speltoides is closer to the B and G genome of polyploid wheats than Aegilops longissima and is the most probable progenitor of these two genomes.
authors.affiliation: Wheat Genetics Resource Center, Kansas State University, Manhattan 66506-5502.
authors.forename: J
authors.initials: J
authors.lastname: Jiang
authors.forename: B S
authors.initials: BS
authors.lastname: Gill
mesh_terms: D005075:Biological Evolution; D002874:Chromosome Mapping; D017343:Genes, Plant / Q000235:genetics*; D011123:Polyploidy; D012337:RNA, Ribosomal, 18S / Q000235:genetics*; D012339:RNA, Ribosomal, 28S / Q000235:genetics*; D014908:Triticum / Q000235:genetics*
chemical_list: D012337:RNA, Ribosomal, 18S; D012339:RNA, Ribosomal, 28S