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Title:Genetic variation of the ribosomal DNA intergenic spacer of maize
Author(s):Kaufman, Benjamin
Doctoral Committee Chair(s):Rocheford, Torbert R.
Department / Program:Department of Ecology, Ethology, and Evolution
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Biology, Molecular
Biology, Genetics
Abstract:Four maize (Zea mays L.) populations selected for grain yield BS10, BS11, RBS10, and RSSSC, were assayed for molecular variation in the ribosomal DNA (rDNA) intergenic spacer (IGS) at initial and advanced cycles of selection. RSSSC and RBS10 underwent reciprocal recurrent selection with an inbred tester in a high yield environment, whereas BS10 and BS11 were subjected to full-sib reciprocal recurrent selection. Maize rDNA, is highly repetitive and shows IGS length variation within and among individuals. Five different ribosomal spacer length variants (rslvs) and a polymorphic SstI restriction site were detected in the four populations. The 5 rslvs and the polymorphic restriction fragment were observed in twenty different combinations, or hybridization fragment patterns (HP). RSSSC, RBS10, and BS11 showed significant changes in the overall rslv and HP frequencies between cycle 0 and the advanced cycle of selection, whereas BS10 did not. In general, two specific HPs were more frequent in the majority of the advanced cycles of the four populations. The frequency changes between initial and advanced cycles were more dramatic for HPs than rslvs. These results are consistent with earlier findings and further support the hypothesis that certain rDNA HPs may be responding to selection for grain yield and may be associated with a selective advantage in US Corn Belt environments.
Most maize rDNA intergenic spacer studies have concentrated on US Corn Belt germplasm. We examined the genetic variation of the maize rDNA IGS region in 70 maize lines/populations from geographically diverse maize growing regions. Despite the very broad scope of the survey, no new rslvs were discovered although many new HPs were observed. Notably, inbred lines from the Corn Belt (CB) exhibited a significantly different frequency distribution of HPs in comparison to non-Corn Belt (NCB) lines. The most frequent HP among the CB and among the NCB inbred lines differed only in the presence/absence of the polymorphic SstI site in the external transcribed spacer region of the IGS. This suggests that sequence variation in the non-repetitive spacer segment might be associated with lines derived from different ecogeographic areas. We further conducted a comparative sequence analysis of the non-repetitive spacer segment from ribosomal transcription repeats within individuals, and among lines that differ for ribosomal HP. A sequence similarity of 92% to 99%, was found among the IGS repeats. Eighty three variable nucleotide positions constituted the variation along the 1.3 kb of spacer examined. Some segments of the sequence were more variable then others. Sequence variation was observed between repeats within an individual plant and among repeats from different lines. DNA sequence variation among repeats within individuals was of the same magnitude as the variation among repeats from different lines. The ribosomal clone that deviated the most from the consensus sequence of all studied repeats corresponds to the 3.4 kb rslv. Therefore, different rslvs may serve as markers of nucleotide variation in the ribosomal ETS.
Issue Date:1995
Rights Information:Copyright 1995 Kaufman, Benjamin
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9543621
OCLC Identifier:(UMI)AAI9543621

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