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At least 37 records · Page 2Linked to original sources
PubMed2002

Molecular phylogeny of hybridizing species from the genus Spartina Schreb. (Poaceae).

Interspecific hybridization events have been reported in the genus Spartina Schreb. (Poaceae), involving the east American species Spartina alterniflora, and including either introgression (e.g., with the western American Spartina foliosa) or allopolyploid speciation (e.g., with the Euro-African Spartina maritima). Molecular phylogenetic analysis of the genus has been undertaken in order to understand phylogenetic relationships and genetic divergence among these hybridizing species. Twelve Spartina species have been sequenced for two nuclear DNA regions (ITS of ribosomal DNA, and part of the Waxy gene) and one chloroplast DNA spacer (trnT-trnL). Separate and conditional combined phylogenetic analyses using Cynodon dactylon as the outgroup have been conducted. Spartina is composed of two lineages. The first clade includes all hexaploid species: the Euro-African S. maritima (2n = 60), the East-American S. alterniflora (2n = 62) and the West-American S. foliosa (2n = 60). Spartina alterniflora appears as a closely related sister species to S. foliosa. Although belonging to the same lineage, Spartina maritima appears consistently more genetically differentiated from S. alterniflora than S. foliosa. The tetraploid species S. argentinensis (2n = 40) is placed at the base of this first clade according to the Waxy data, but its position is not well resolved by the other sequences. The second well-supported main lineage within genus Spartina includes the other tetraploid American species. Significant incongruence has been encountered between the waxy based tree and both the ITS and trnT-trnL trees concerning the position of S. densiflora, suggesting a possible reticulate evolution for this species. The results agree with hybridization patterns occurring in Spartina: introgression involving closely related species (S. alterniflora and S. foliosa) on one hand, and alloploid speciation involving more differentiated species (S. alterniflora and S. maritima) on the other hand.

Cell Nucleus↗
PubMed1992

Evolution of Ac and Dsl elements in select grasses (Poaceae).

We present data on evolution of the Ac/Ds family of transposable elements in select grasses (Poaceae). An Ac-like element was cloned from a DNA library of the grass Pennisetum glaucum (pearl millet) and 2387 bp of it have been sequenced. When the pearl millet Ac-like sequence is aligned with the corresponding region of the maize Ac sequence, it is found that all sequences corresponding to intron II in maize Ac are absent in pearl millet Ac. Kimura's evolutionary distance between maize and pearl millet Ac sequences is estimated to be 0.429 +/- 0.020 nucleotide substitutions per site. This value is not significantly different from the average number of synonymous substitutions for coding regions of the Adh1 gene between maize and pearl millet, which is 0.395 +/- 0.051 nucleotide substitutions per site. If we can assume Ac and Adh1 divergence times are equivalent between maize and pearl millet, then the above calculations suggest Ac-like sequences have probably not been strongly constrained by natural selection. The level of DNA sequence divergence between maize and pearl millet Ac sequences, the estimated date when maize and pearl millet diverged (25-40 million years ago), coupled with their reproductive isolation/lack of current genetic exchange, all support the theory that Ac-like sequences have not been recently introduced into pearl millet from maize. Instead, Ac-like sequences were probably present in the progenitor of maize and pearl millet, and have thus existed in the grasses for at least 25 million years. Ac-like sequences may be widely distributed among the grasses. We also present the first 2 Ds1 controlling element sequences from teosinte species: Zea luxurians and Zea perennis. A total of 10 Ds1 elements had previously been sequenced from maize and a distant maize relative, Tripsacum. When a maximum likelihood network of genetic relationships is constructed for all 12 sequenced Ds1 elements, the 2 teosinte Ds1 elements are as distant from most maize Ds1 elements and from each other, as the maize Ds1 elements are from one another. Our new teosinte sequence data support the previous conclusion that Ds1 elements have been accumulating mutations independently since maize and Tripsacum diverged. We present a scenario for the origin of Ds1 elements.

Amino Acid Sequence↗
PubMed1993

A chloroplast DNA mutational hotspot and gene conversion in a noncoding region near rbcL in the grass family (Poaceae).

The noncoding DNA region of the chloroplast genome, flanked by the genes rbcL and psaI (ORF36), has been sequenced for seven species of the grass family (Poaceae). This region had previously been observed as a hotspot area for length mutations. Sequence comparison reveals that short duplications, probably resulting from slipped-strand mispairing, account for many small length differences between sequences but that major mutational hotspots are localized in three small areas, two of which show potential secondary structure. Mutation in one of these hotspots appears to be a result of more complex recombination events. All seven species contain a pseudogene for rpl23 and evidence is presented that this pseudogene is being maintained by gene conversion with the functional gene. Different transition/transversion biases and AT contents between the pseudogene and the surrounding noncoding sequences are noted. In the subfamily Panicoideae there is a deletion in which almost 1 kb of ancestral sequence, including the 3' end of the rpl23 pseudogene, has been replaced by a non-homologous 60-base sequence of unknown origin. Two other deletions of almost the same region have occurred in the grass family. The deleted noncoding region has mutational and compositional properties similar to the rbcL coding sequence and the rpl23 pseudogene. The three independent deletions, as well as the pattern of mutation in the localized hotspots, indicate that such noncoding DNA may be misleading for studies of phylogenetic inference.

Base Sequence↗
PubMed2000

Probing meiosis in hybrids of Lolium (Poaceae) with a discriminatory repetitive genomic sequence.

A moderately repetitive genomic DNA sequence (designated pLPBB2-123) derived from Lolium perenne L. (Poaceae) is considerably more abundant in the genome of this species than in that of the closely related L. temulentum. The repetitive sequence probe is clearly able to discriminate between the genomic DNA of both species in Southern analysis, and effectively 'paints' only the chromosome set of L. perenne in diploid and triploid hybrids with L. temulentum. Fluorescence in situ hybridisation of this sequence onto homologous chromosomes during meiosis I of the hybrids shows that the sequence is evenly distributed along all of the chromosomes of L. perenne and appears to have little effect on the structural integrity or recombination potential of hybrid bivalents. Discrimination between chromatin of different parental origin in hybrid bivalents shows for the first time a progressive relaxation of relational coiling of homoeologues throughout meiotic prophase. It also highlights structural irregularities that can now be unequivocally assigned to the longer chromosomes of L. temulentum. The advantages of the use of specific differentially amplified sequences instead of whole genome probes are discussed within the context of introgression breeding programmes within the Lolium/Festuca complex.

Chromosomes↗
PubMed2003

The influence of temperature, relative humidity and rainfall on the occurrence of pollen allergens (Betula, Poaceae, Ambrosia artemisiifolia) in the atmosphere of Bratislava (Slovakia).

The occurrence of pollen grains in the atmosphere markedly relates to meteorological factors. In the study we have evaluated a correlation between the concentration of pollen grains in the atmosphere of Bratislava and temperature, relative humidity and rainfall during the vegetation period of 1995 and 1997. For our analysis we have selected one representative of each phytoallergen group (trees, grasses, weeds). We have chosen the Betula genus of trees, the whole Poaceae family of grasses and ragweed Ambrosia artemisiifolia L. to represent weeds. The taxons mentioned represent the most significant allergens in Slovakia. The concentration of pollen grains has been monitored by a Lanzoni volumetric pollen trap. The data obtained, the average daily concentration in 1 m(3), have been included in the statistical analysis together with values for the average daily temperature, relative humidity and total rainfall in 24 h. The correlation between the concentration of pollen grains in the atmosphere and selected meteorological variables from daily monitoring has been studied with the help of linear regression and correlation coefficients. We have found the average daily temperature and relative humidity (less than temperature) to be significant factors influencing the occurrence of pollen grains in the atmosphere of Bratislava. The total daily rainfall does not seem to be significant from the statistical point of view.

Allergens↗
PubMed2001

Forecasting the start of the pollen season of Poaceae: evaluation of some methods based on meteorological factors.

The pollen of anemogamous plants is responsible for half the allergic diseases, that is to say a prevalence of 10% in the French population. Poaceae produce the first allergenic pollen almost everywhere. The work described in this article aimed to validate forecast methods for the use of physicians and allergic people who need accurate and early information on the first appearance of pollen in the air. The methods were based on meteorological parameters, mainly temperature. Four volumetric Hirst traps were used from 1995 to 1998, situated in two departments of Burgundy. Two of the methods tested proved to be of particular interest: the sum of the temperatures and the sum of Q10 values, an agrometeorological coefficient integrating temperature. A multiple regression, using maximum temperature and rainfall, was also performed but it gave slightly less accurate results. A chi 2-test was then used to compare the accuracy of the three methods. It was found that the date of onset of the pollen season could be predicted early enough to be useful in medical practice. Results were verified in 1999, and the research must be continued to obtain better statistical validity.

Allergens↗
PubMed2005

Phylogeny of Eleusine (Poaceae: Chloridoideae) based on nuclear ITS and plastid trnT-trnF sequences.

Phylogenetic relationships in the genus Eleusine (Poaceae: Chloridoideae) were investigated using nuclear ITS and plastid trnT-trnF sequences. Separate and combined data sets were analyzed using parsimony, distance, and likelihood based methods, including Bayesian. Data congruence was examined using character and topological measures. Significant data heterogeneity was detected, but there was little conflict in the topological substructure measures for triplets and quartets, and resolution and clade support increased in the combined analysis. Data incongruence may be a result of noise and insufficient information in the slower evolving trnT-trnF. Monophyly of Eleusine is strongly supported in all analyses, but basal relationships in the genus remain uncertain. There is good support for a CAIK clade (E. coracana subsp. coracana and africana, E. indica, and E. kigeziensis), with E. tristachya as its sister group. Two putative ITS homeologues (A and B loci) were identified in the allotetraploid E. coracana; the 'B' locus sequence type was not found in the remaining species. Eleusine coracana and its putative 'A' genome donor, the diploid E. indica, are confirmed close allies, but sequence data contradicts the hypothesis that E. floccifolia is its second genome donor. The 'B' genome donor remains unidentified and may be extinct.

Base Sequence↗
PubMed2005

Differentiation of important and closely related cereal plant species (Poaceae) in food by hybridization to an oligonucleotide array.

We report the development of an oligonucleotide microarray for the simultaneous detection of six important cereal food plant species from the Poaceae based on the chloroplast trnL intron sequence. We used universal primers to amplify the trnL intron from wheat, rye, barley, oat, rice, and maize, followed by a cyclic labeling of oligonucleotides probes and subsequent hybridization to an oligonucleotide microarray. In single taxon analyses, positive signals were produced with a high signal-to-noise ratio. The assay also enabled the analysis of mixed samples. The results obtained for real food samples were in agreement with the ingredient labels, but positive results for grains not declared on the ingredients list were observed in three out of 10 samples, which indicates that the final products and/or the declared ingredients were probably botanically impure or contaminated. The combination of the sensitivity of a universal polymerase chain reaction with the specificity of the labeling reaction allows this protocol to be applied in routine analyses of food samples, as demonstrated by successful analysis of processed composite food products.

DNA, Plant↗
PubMed2003

Characteristics and behaviour of the chromosomes of Leymus mollis and L. racemosus (Triticeae, Poaceae) during mitosis and meiosis.

Leymus mollis and L. racemosus (Triticeae; Poaceae) are important as genetic resources for wheat improvement, as they carry genes for salt tolerance and disease resistance. Even though these species share common Ns and Xm genomes, the genomic relationship between these two species is not yet clearly understood. In this study, we examined the genomes of the two species by FISH and GISH, using combinations of tandem-repetitive sequences and genomic DNAs. Comparative GISH showed that genomes in the genus Leymus were diverse. Nevertheless, chromosomes of these two species were able to undergo complete meiotic pairing in hybrids, suggesting that differences in the subtelomeric heterochromatin and sequences distinguishable by GISH do not affect meiotic pairing.

Chromosome Pairing↗
PubMed2002

Building supertrees: an empirical assessment using the grass family (Poaceae).

Large and comprehensive phylogenetic trees are desirable for studying macroevolutionary processes and for classification purposes. Such trees can be obtained in two different ways. Either the widest possible range of taxa can be sampled and used in a phylogenetic analysis to produce a "big tree," or preexisting topologies can be used to create a supertree. Although large multigene analyses are often favored, combinable data are not always available, and supertrees offer a suitable solution. The most commonly used method of supertree reconstruction, matrix representation with parsimony (MRP), is presented here. We used a combined data set for the Poaceae to (1) assess the differences between an approach that uses combined data and one that uses different MRP modifications based on the character partitions and (2) investigate the advantages and disadvantages of these modifications. Baum and Ragan and Purvis modifications gave similar results. Incorporating bootstrap support associated with pre-existing topologies improved Baum and Ragan modification and its similarity with a combined analysis. Finally, we used the supertree reconstruction approach on 55 published phylogenies to build one of most comprehensive phylogenetic trees published for the grass family including 403 taxa and discuss its strengths and weaknesses in relation to other published hypotheses.

Data Interpretation, Statistical↗
PubMed2005

Anatomical features and ultrastructure of Deschampsia antarctica (Poaceae) leaves from different growing habitats.

BACKGROUND AND AIMS: The leaf anatomy and ultrastructure of Deschampsia antarctica (Poaceae) plants growing in three different habitats (a dry site in the Antarctic tundra, a wet site in a zone exposed to sea spray and a greenhouse) were investigated. The ultrastructure of the leaves of D. antarctica has not been studied before. METHODS: Semi-thin sections of the D. antarctica leaves were stained with toluidine blue and viewed using a light microscope. Ultra-thin sections stained with uranyl acetate and lead citrate were examined using a transmission electron microscope. KEY RESULTS: Plants growing in the Antarctic tundra and in a greenhouse had stronger xerophytic features than those growing at the seashore. The stress response of D. antarctica plants growing in the wet environment, exposed to high salinity and flooding, included: irregular mesophyll cells, large intercellular spaces in the parenchymatic layer, bulliform epidermal cells and vascular bundles surrounded with deformed outer and inner bundle sheaths of leaves. The highest number of sclerenchymatic fibres is characteristic of the leaves of plants growing in a greenhouse, whereas the smallest was of plants growing in a wet habitat. Stress conditions can disturb the formation of sclerenchymatic fibres. In plants growing in the Maritime Antarctic the chloroplasts of the mesophyll cells of leaves are of an irregular shape, with pockets or invaginations inside the organelles and outgrowths. Both of them make the surfaces of chloroplasts larger, and result in an increase in the amount of substances exchanged between the chloroplasts and cytoplasm or the other organelles. The leaf mesophyll cells of D. antarctica plants growing in Antarctica contain atypical structures including numerous vesicles of different sizes and concentrically arranged membranes. CONCLUSIONS: The anatomical and ultrastructural features of the leaf and their changes under stress conditions are considered in relation to the adaptations of D. antarctica to the climate conditions in the Maritime Antarctic.

Antarctic Regions↗
PubMed2005

NADP-malate dehydrogenase gene evolution in Andropogoneae (Poaceae): gene duplication followed by sub-functionalization.

BACKGROUND AND AIMS: Plastid NADP-dependent malate dehydrogenase (MDH) catalyses the conversion of oxaloacetate to malate. In C4 plants, it is involved in photosynthetic carbon assimilation. In Poaceae, one NADP-MDH gene has been identified in rice (C3; Erhartoideae) and maize (C4; Panicoideae), whereas two tandemly repeated genes have been identified in Sorghum (C4; Panicoideae). In the present study, the molecular evolution of the NADP-MDH multigene family was investigated in order to analyse how the C4 isoform has evolved over a broader range of panicoid grasses. METHODS: Polymerase chain reaction (PCR)-based cloning was used to isolate cDNAs encoding NADP-MDHs from 15 species of Panicoideae. A gene phylogeny was reconstructed based on cDNA sequences using distance and maximum parsimony methods. Episodic selection along some branches of the phylogenetic tree was tested by analysing non-synonymous and synonymous rate ratios. Transcription of NADP-MDH genes was compared in green leaves of five accessions of Saccharum, Sorghum and Vetiveria using a semi-quantitative PCR approach. KEY RESULTS: Phylogenetic analyses of these data support the existence of two NADP-MDH gene lineages (NMDH-I and NMDH-II) in several Andropogoneae (i.e. Saccharum, Sorghum and Vetiveria). Episodic positive selection was shown along the basal branch of the NMDH-II clade. Three amino acid modifications allow the two gene lineages to be distinguished, suggesting a positive selection at these sites. In green leaves, we showed that the transcript accumulation was higher for NMDH-I than for NMDH-II. CONCLUSIONS: It is hypothesized that the maintenance of both NADP-MDH genes in some Andropogoneae is due to a partition of the original functions across both copies. NMDH-I probably corresponds to the C4 isoform as previously suggested. Nevertheless, some C4 species (e.g. maize) only have one gene which should be selected for its high expression level in leaves. This study confirms that gene duplicates have been recruited for C4 photosynthesis but are not required in every case.

Evolution, Molecular↗
PubMed2000

Gene flow in a facultative apomictic poacea, the savanna grass Hyparrhenia diplandra.

The genetics of the poacea Hyparrhenia diplandra was studied in four natural populations from an ecological station in West Africa, where it makes up 80% of grasses from wet savanna and constitutes a dense continuum of randomly distributed individuals. DNA content and cytogenetical observations suggest it is an allotetraploid. Using two highly variable microsatellites (heterozygosity H = 0.615-0.616), we show that this species is an apomict with rare sexual reproduction events that account for approximately 0.5% of seeds pollinated in the wild. Hexaploid individuals were also produced, corroborating the observation of aberrant genotypes in the wild. The spatial extent of asexual clones in the field was low in comparison with the predominance of apomixis, thus indicating a low dispersal of seeds from their parent. Heterozygosity and departure from Hardy-Weinberg predictions were similar in the four populations, revealing a high apparent selfing rate s = 0.599 among sexually produced seeds. This is an overestimate since we could not distinguish true selfing from reciprocal outcrosses between neighboring individuals from the same apomictic clone. Gene flow by pollen could be substantial, possibly explaining the absence of isolation by distance in the studied area.

Africa, Western↗
PubMed2002

Effects of low chronic doses of ionizing radiation on antioxidant enzymes and G6PDH activities in Stipa capillata (Poaceae).

Stipa capillata (Poaceae) seeds were harvested from a control area (displaying a gamma dose rate of 0.23 micro Sv h(-1)) (C plants) and from two contaminated areas (5.4 and 25 micro Sv h(-1)) on the Semipalatinsk nuclear test site (SNTS) in Kazakhstan. The plants were grown for 124 d in a greenhouse under controlled conditions and exposed to three different treatments: (0) control; (E) external gamma irradiation delivered by a sealed 137Cs source with a dose rate of 66 micro Sv h(-1); (E+I) E treatment combined with internal beta irradiation due to contamination by 134Cs and 85Sr via root uptake from the soil. The root uptake led to a contamination of 100 Bq g(-1) for 85Sr and 5 Bq g(-1) for 134Cs (of plant dry weight) as measured at harvest. The activity of SOD, APX, GR, POD, CAT, G6PDH, and MDHAR enzymes was measured in leaves. Under (0) treatment, all enzymes showed similar activities, except POD, which had higher activity in plants originating from contaminated areas. Treatment (E) induced an enhancement of POD, CAT, GR, SOD, and G6PDH activities in plants originating from contaminated areas. Only control plants showed any stimulation of APX activity. Treatment (E+I) had no significant effect on APX, GR, CAT, and POD activities, but MDHAR activity was significantly reduced while SOD and G6PDH activities were significantly increased. The increase occurred in plants from all origins for SOD, with a greater magnitude as a function of their origin, and it occurred only in plants from the more contaminated populations for G6PDH. This suggests that exposure to a low dose rate of ionizing radiation for almost a half century in the original environment of Stipa has led to natural selection of the most adapted genotypes characterized by an efficient induction of anti-oxidant enzyme activities, especially SOD and G6PDH, involved in plant protection against reactive oxygen species.

Ascorbate Peroxidases↗
PubMed2005

Molecular evolution of FLORICAULA/LEAFY orthologs in the Andropogoneae (Poaceae).

Members of the grass family (Poaceae) exhibit a broad range of inflorescence structures and other morphologies, making the grasses an interesting model system for studying the evolution of development. Here we present an analysis of the molecular evolution of FLORICAULA/LEAFY-like genes, which are important developmental regulatory loci known to affect inflorescence development in a wide range of flowering plant species. We have focused on sequences from the Andropogoneae, a tribe within the grass family that includes maize (Zea mays ssp. mays) and Sorghum (Sorghum bicolor). The FLORICAULA/LEAFY gene phylogeny we generated largely agrees with previously published phylogenies for the Andropogoneae using other nuclear genes but is unique in that it includes both members of one of the many duplicate gene sets present in maize. The placement of these sequences in the phylogeny suggests that the duplication of the maize FLORICAULA/LEAFY orthologs, zfl1 and zfl2, is a consequence of a proposed tetraploidy event that occurred in the common ancestor of Zea and a closely related genus, Tripsacum. Our data are consistent with the hypothesis that the transcribed regions of the FLORICAULA/LEAFY-like genes in the Andropogoneae are functionally constrained at both nonsynonymous and synonymous sites and show no evidence of directional selection. We also examined conservation of short noncoding sequences in the first intron, which may play a role in gene regulation. Finally, we investigated the genetic diversity of one of the two maize FLORICAULA/LEAFY orthologs, zfl2, in maize and its wild ancestor, teosinte (Z. mays ssp. parviglumis), and found no evidence for selection pressure resulting from maize domestication within the zfl2-coding region.

Base Sequence↗
PubMed1996

The phytochrome gene family in grasses (Poaceae): a phylogeny and evidence that grasses have a subset of the loci found in dicot angiosperms.

The phytochrome nuclear gene family encodes photoreceptor proteins that mediate developmental responses to red and far red light throughout the life of the plant. From studies of the dicot flowering plant Arabidopsis, the family has been modeled as comprising five loci, PHYA-PHYE. However, it has been shown recently that the Arabidopsis model may not completely represent some flowering plant groups because additional PHY loci related to PHYA and PHYB of Arabidopsis apparently have evolved independently several times in dicots, and monocot flowering plants may lack orthologs of PHYD and PHYE of Arabidopsis. Nonetheless, the phytochrome nucleotide data were informative in a study of organismal evolution because the loci occur as single copy sequences and appear to be evolving independently. We have continued our investigation of the phytochrome gene family in flowering plants by sampling extensively in the grass family. The phytochrome nuclear DNA data were cladistically analyzed to address the following questions: (1) Are the data consistent with a pattern of differential distribution of phytochrome genes among monocots and higher dicots, with homologs of PHYA, B, C, D, and E present in higher dicots, but of just PHYA, B, and C in monocots, and (2) what phylogenetic pattern within Poaceae do they reveal? Results of these analyses, and of Southern blot experiments, are consistent with the observation that the phytochrome gene family in grasses comprises the same subset of loci detected in other monocots. Furthermore, for studies of organismal phylogeny in the grass family, the data are shown to provide significant support for relationships that are just weakly resolved by other data sets.

Blotting, Southern↗
PubMed1999

Patterns of genetic diversification within the Adh gene family in the grasses (Poaceae).

We investigated the evolutionary dynamics of the Adh gene family within the grasses (Poaceae), with the goal of using molecular evolutionary tools to understand the process of gene family diversification. We analyzed 21 Adh sequences representing a broad array of grasses. Phylogenetic analyses suggested that Adh duplicated into Adh1 and Adh2 before the radiation of the grasses roughly 65 MYA. Gene structure, including intron length, has varied little over this period. Conservation of intron length prompted investigation into the dynamics of intron evolution, particularly the ability of intron sequences to form secondary structures. Intron sequences did not have an extremely high or low minimum free energy of folding relative to permuted sequences, suggesting that individual Adh introns do not evolve under secondary structural constraints. For coding sequences, the diversification of Adh1 and Adh2 was marked by a shift in third-position G + C content. This shift may reflect differential selection for codon use. Diversification between Adh1 and Adh2 was also typified by a shift in nonsynonymous nucleotide substitution rates, but there was no evidence that relatively fast nonsynonymous nucleotide substitution rates in the Adh2 clade were a product of diversifying selection. Gene conversion may have played a role in retarding diversification of Adh1 and Adh2 in rice, but there is no evidence of gene conversion between paralogs in other taxa. Although the reasons for retention of two functional Adh genes remain obscure, we propose that a shift in gene expression was important for the retention of the two Adh gene copies within the grasses.

Alcohol Dehydrogenase↗
PubMed1994

Slipped-strand mispairing in a plastid gene: rpoC2 in grasses (Poaceae).

An exception to the generally conservative nature of plastid gene evolution is the gene coding for the beta" subunit of RNA polymerase, rpoC2. Previous work by others has shown that maize and rice have an insertion in the coding region of rpoC2, relative to spinach and tobacco. To assess the distribution of this extra coding sequence, we surveyed a broad phylogenetic sample comprising 55 species from 17 angiosperm families by using Southern hybridization. The extra coding sequence is restricted to the grasses (Poaceae). DNA sequence analysis of 11 species from all five subfamilies within the grass family demonstrates that the extra sequence in the coding region of rpoC2 is a repetitive array that exhibits more than a twofold increase in nucleotide substitution, as well as a large number of insertion/deletion events, relative to the adjacent flanking sequences. The structure of the array suggests that slipped-strand mispairing causes the repeated motifs and adds to the mechanisms through which the coding sequence of plastid genes are known to evolve. Phylogenetic analyses based on the sequence data from grass species support several relationships previously suggested by morphological work, but they are ambiguous about broad relationships within the family.

Base Sequence↗