Evolution of DNA sequence organization in mitochondrial genomes of Zea

Abstract

Molecular mechanisms underlying the evolution of mtDNA in maize and three species of teosinte have been investigated. By using DNA transfer techniques and cloned fragments of maize mtDNA, changes in the position of homologous sequences in restriction digests were analyzed in related taxa. The resulting patterns indicate general conservation of sequence homology in all four species. One-third of the cloned fragments showed sequences conserved in homology and position of BamHI restriction fragments. Other fragments produced patterns indicating that extensive rearrangement of DNA sequences has taken place. In two cases, hybridization patterns revealed major changes in relative abundance of specific sequences that we believe are related to the molecular heterogeneity phenomenon of maize mtDNA. The evolution of mtDNA in these plants appears dramatically different from that in animal mtDNA, where base substitutions may account for most of the observed changes in restriction patterns.Evolution of higher plants must involve the distinct genomes of the nucleus, chloroplast, and mitochondrion. In the genus Zea, L., both organelle genomes show strict maternal inheritance (1-3) that greatly restricts the sources of variation for evolution provided by sexual cycles and biparental inheritance.In contrast to animal mtDNA, which typically has a size of 10 megadaltons (MDal) per mitochondrial genome, plant mtDNA is far more complex (4-10)-e.g., the maize mitochondrial genome has been estimated to be 320 MDal (8). In addition to larger size, plant mtDNA is characterized by molecular heterogeneity (4-7) observed as classes ofcircular chromosomes that vary in size and relative abundance. To learn about the molecular events that have occurred in the evolution of these unusual DNAs, we have directed our attention to the mtDNAs of maize and its closest relatives, the teosintes.Restriction enzyme digests of organelle DNAs from several races of teosinte have been analyzed previously (9). Groupings based on restriction patterns approximate the biosystematic relationships of the taxa. Perennial teosinte, Z. perennis (Hitch) Reeves and Manglesdorf, is the only tetraploid in the genus (2n = 40). Race Guatemala, Z. luxurians (Durieu and Ascherson) Bird, an annual diploid (2n = 20), is genetically the most distinct from maize. Another annual diploid race, Central Plateau, Zea mays ssp. mexicana (Schrader) Iltis, has close affinities to maize (11). Hybridization of teosinte and maize accompanied by introgression and differentiation has modified Zea populations to various degrees (11,12). Central Plateau (CP) was selected as representative of many annual teosintes; Guatemala (Gu) and perennial (ZP) teosinte were selected because their mtDNAs are distinct from each other and each differs greatly from maize and other teosintes (9). Although organelle DNA variation within these taxa has been recognized (9), the range of variation is not addressed in this study.Restriction digests fractionated on agarose gels and visualized by fluorescent s...

DNA changes involving repeated sequences in senescing soybean (Glycine max) cotyledon nuclei

“…Bacterial colonies were grown on nitrocellulose filters and treated by the method of Grunstein and Hogness (1975) with the modification of Sederoff et al (1981). Nitrocellulose filters were placed on 3 MM paper saturated with 0.5 M NaOH for 5 min and neutralized by transfer to 3 MM paper with 1 M Tris-HCl, pH 7.5, for 5 min.…”

Multiple sequence rearrangements accompanying the duplication of a tRNAPro gene in wheat mitochondrial DNA

“…Analysis of restriction patterns has revealed extensive variation in the structure of m t D N A from some closely related plant species [e.g., 47], and comparison of available gene maps [9,26,53] indicates that there is virtually no conservation of gene arrangement in plant mtDNA, with the exception of a close linkage of 18S and 5S rRNA genes [18]. In these respects, the plant mitochondrial genome is quite unlike its counterpart in vertebrate animals, which is small, shows little size variation, diverges in sequence at a relatively rapid rate within coding sequences, and has maintained an invariant gene order throughout 500 million years of chordate evolution [1,6,46].…”

Genetic discontinuity revealed by chloroplast microsatellites in eastern North American Abies (Pinaceae)

“…At the level of nuclear genes, interbreeding and genetic exchange obscure the evidence of past demographic patterns. In plants, mitochondrial genomes have not typically been useful for phylogenetic analysis due to a high rate of sequence reorganization (Sederoff et al, 1981;Wu, Krutovskii, and Strauss, 1998). Conifers often display minimal levels of differentiation among populations and high levels of genetic diversity at loci in the nuclear genome (Hamrick andGodt, 1990, 1996).…”

“…In these organelles, effective population size is approximately one-half that of nuclear genes (McCauley, 1995) and, consequently, both the time to allele fixation within populations and response time to stochastic change are reduced. In plants, mitochondrial genomes have not typically been useful for phylogenetic analysis due to a high rate of sequence reorganization (Sederoff et al, 1981;Wu, Krutovskii, and Strauss, 1998). Mitochondrial haplotype diversity related to sequence rearrangement has, however, shown utility in population differentiation of pine and fir taxa (Strauss, Hong, and Hipkins, 1993;Tsumura and Suyama, 1998).…”