Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2005
Publication Date: 5/10/2006
Citation: Wang, R., Zhang, J.Y., Lee, B.S., Jensen, K.B., Kishii, M., Tsujimoto, H. 2006. Variation in abundance of two repetitive sequences in leymus and psathyrostachys species. Genome 49:511-519 Interpretive Summary: Repetitive DNA sequences account for 80% or more of the DNA content in Triticeae species. The old school of thought holds that repetitive sequences are "junk DNA" without biological functions. As new evidence accumulates, it is now realized that some repetitive sequences in animal and plant genomes play important biological functions that affect gene expression, thus determining morphology and adaptation of the organism. In surveying the variation of two repetitive sequences (TaiI and PstI families) in two genera Leymus and Psathyrostachys, we observed wide variation ranging from total absence to a large number of sites in many chromosomes. Thus, it can be concluded that these two repetitive sequences are neither genome - nor chromosome-specific markers. But it is highly possible that they are involved in regulating gene expression and affecting plant morphology, thus playing a role in species adaptation and geographic distribution.
Technical Abstract: The Ns genome of the genus Psathyrostachys is a component of the polyploid genome in the genus Leymus. The occurrence and abundance of two tandem repetitive sequences, pLrTaiI-1 (TaiI family) and pLrPstI-1 (one class of 350-bp family) that were isolated from Leymus racemosus (Lam.) Tzvelev, were assayed in four species each of the genus Psathyrostachys and Leymus using fluorescence in situ hybridization (FISH). The pLrPstI-1 sequence was absent in all four Psathyrostachys species. While P. fragilis and P. huashanica did not have the pLrTaiI-1 sequence, 15 accessions of P. juncea had pLrTaiI-1 FISH sites ranging from 7 to 16, whereas two accessions of P. lanuginosa had pLrTaiI-1 sites ranging from 2 to 21. In Leymus, number of pLrTaiI-1 and pLrPstI-1 sites were 1 to 24 and 0 to 30, respectively, in L. ramosus, 2 to 31 and 5 to 36 in L. racemosus, 0 to 4 and 0 in L. mollis, 2 to 9 and 24 to 27 in L. secalinus. The FISH assay on pLrTaiI-1 was successfully converted to a sequence-tagged-site polymerase chain reaction (STS-PCR) test using a primer pair designed from DNA sequence of this repetitive DNA. Seventy-three accessions representing 27 Leymus species were assayed for the abundance of pLrTaiI-1 by STS-PCR. With a few exceptions of uniformity in some accessions/species, nearly all species were heterogeneous for the abundance of pLrTaiI-1 sequence and no Leymus species was totally devoid of this repetitive sequence. These findings may have significance on understanding of phylogeny, nature of polyploidy, adaptive ranges and breeding potential of Leymus species.