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At least 325 records · Page 18Linked to original sources
PubMed2006

Analysis of a xyloglucan endotransglycosylase/hydrolase (XTH) from the lycopodiophyte Selaginella kraussiana suggests that XTH sequence characteristics and function are highly conserved during the evolution of vascular plants.

A tissue print followed by a xyloglucan endotransglycosylase assay revealed that XET activity is present at sites of cell elongation in both roots and shoots of the lycopodiophyte Selaginella kraussiana. This paper provides the first report and analysis of a xyloglucan endotransglycosylase/hydrolase (XTH) cDNA sequence, isolated from a club moss. In silico analysis of the deduced amino acid sequence revealed a strong conservation of the XET-domain described in higher plants. The catalytic site (DEIDLEFLG) varies in only one amino acid compared with the consensus sequence and was shown to be functional after recombinant expression of Sk-XTH1 in Pichia pastoris. Sk-XTH1 displays xyloglucan endotransglycosylase activity over a broad pH (4.5-7.5) and temperature range (4-30 degrees C), but it shows no hydrolase activity. The catalytic site is followed by a consensus sequence for N-linked glycosylation. Four terminal cysteines were shown to stabilize a putative XET-C terminal extension region, which includes conserved amino acids, involved in the recognition and binding of the substrates. The N-linked sugar interactions as well as the disulphide bridges were shown to be necessary to perform XET activity. The presence of a highly conserved XTH sequence and function in a microphyllophyte suggests that XTHs were present before the divergence of lycopodiophytes and euphyllophytes. It also points to a possible key role for XTHs in the production of a cell wall that allowed the further evolution of land plants.

Amino Acid Sequence↗
PubMed2004

Reconstruction of putative DNA virus from endogenous rice tungro bacilliform virus-like sequences in the rice genome: implications for integration and evolution.

BACKGROUND: Plant genomes contain various kinds of repetitive sequences such as transposable elements, microsatellites, tandem repeats and virus-like sequences. Most of them, with the exception of virus-like sequences, do not allow us to trace their origins nor to follow the process of their integration into the host genome. Recent discoveries of virus-like sequences in plant genomes led us to set the objective of elucidating the origin of the repetitive sequences. Endogenous rice tungro bacilliform virus (RTBV)-like sequences (ERTBVs) have been found throughout the rice genome. Here, we reconstructed putative virus structures from RTBV-like sequences in the rice genome and characterized to understand evolutionary implication, integration manner and involvements of endogenous virus segments in the corresponding disease response. RESULTS: We have collected ERTBVs from the rice genomes. They contain rearranged structures and no intact ORFs. The identified ERTBV segments were shown to be phylogenetically divided into three clusters. For each phylogenetic cluster, we were able to make a consensus alignment for a circular virus-like structure carrying two complete ORFs. Comparisons of DNA and amino acid sequences suggested the closely relationship between ERTBV and RTBV. The Oryza AA-genome species vary in the ERTBV copy number. The species carrying low-copy-number of ERTBV segments have been reported to be extremely susceptible to RTBV. The DNA methylation state of the ERTBV sequences was correlated with their copy number in the genome. CONCLUSIONS: These ERTBV segments are unlikely to have functional potential as a virus. However, these sequences facilitate to establish putative virus that provided information underlying virus integration and evolutionary relationship with existing virus. Comparison of ERTBV among the Oryza AA-genome species allowed us to speculate a possible role of endogenous virus segments against its related disease.

Amino Acid Sequence↗
PubMed2000

Transposable element contributions to plant gene and genome evolution.

Transposable elements were first discovered in plants because they can have tremendous effects on genome structure and gene function. Although only a few or no elements may be active within a genome at any time in any individual, the genomic alterations they cause can have major outcomes for a species. All major element types appear to be present in all plant species, but their quantitative and qualitative contributions are enormously variable even between closely related lineages. In some large-genome plants, mobile DNAs make up the majority of the nuclear genome. They can rearrange genomes and alter individual gene structure and regulation through any of the activities they promote: transposition, insertion, excision, chromosome breakage, and ectopic recombination. Many genes may have been assembled or amplified through the action of transposable elements, and it is likely that most plant genes contain legacies of multiple transposable element insertions into promoters. Because chromosomal rearrangements can lead to speciating infertility in heterozygous progeny, transposable elements may be responsible for the rate at which such incompatibility is generated in separated populations. For these reasons, understanding plant gene and genome evolution is only possible if we comprehend the contributions of transposable elements.

DNA Transposable Elements↗
PubMed2001

Chloroplast microsatellites: new tools for studies in plant ecology and evolution.

The nonrecombinant, uniparentally inherited nature of organelle genomes makes them useful tools for evolutionary studies. However, in plants, detecting useful polymorphism at the population level is often difficult because of the low level of substitutions in the chloroplast genome, and because of the slow substitution rates and intramolecular recombination of mtDNA. Chloroplast microsatellites represent potentially useful markers to circumvent this problem and, to date, studies have demonstrated high levels of intraspecific variability. Here, we discuss the use of these markers in ecological and evolutionary studies of plants, as well as highlighting some of the potential problems associated with such use.

Journal Article↗
PubMed2001

Human-caused environmental change: impacts on plant diversity and evolution.

Human-caused environmental changes are creating regional combinations of environmental conditions that, within the next 50 to 100 years, may fall outside the envelope within which many of the terrestrial plants of a region evolved. These environmental modifications might become a greater cause of global species extinction than direct habitat destruction. The environmental constraints undergoing human modification include levels of soil nitrogen, phosphorus, calcium and pH, atmospheric CO(2), herbivore, pathogen, and predator densities, disturbance regimes, and climate. Extinction would occur because the physiologies, morphologies, and life histories of plants limit each species to being a superior competitor for a particular combination of environmental constraints. Changes in these constraints would favor a few species that would competitively displace many other species from a region. In the long-term, the "weedy" taxa that became the dominants of the novel conditions imposed by global change should become the progenitors of a series of new species that are progressively less weedy and better adapted to the new conditions. The relative importance of evolutionary versus community ecology responses to global environmental change would depend on the extent of regional and local recruitment limitation, and on whether the suite of human-imposed constraints were novel just regionally or on continental or global scales.

Biological Evolution↗
PubMed2000

The origin and early evolution of tracheids in vascular plants: integration of palaeobotanical and neobotanical data.

Although there is clear evidence for the establishment of terrestrial plant life by the end of the Ordovician, the fossil record indicates that land plants remained extremely small and structurally simple until the Late Silurian. Among the events associated with this first major radiation of land plants is the evolution of tracheids, complex water-conducting cells defined by the presence of lignified secondary cell wall thickenings. Recent palaeobotanical analyses indicate that Early Devonian tracheids appear to possess secondary cell wall thickenings composed of two distinct layers: a degradation-prone layer adjacent to the primary cell wall and a degradation-resistant (possibly lignified) layer next to the cell lumen. In order to understand better the early evolution of tracheids, developmental and comparative studies of key basal (and potentially plesiomorphic) extant vascular plants have been initiated. Ultrastructural analysis and enzyme degradation studies of wall structure (to approximate diagenetic alterations of fossil tracheid structure) have been conducted on basal members of each of the two major clades of extant vascular plants: Huperzia (Lycophytina) and Equisetum (Euphyllophytina. This research demonstrates that secondary cell walls of extant basal vascular plants include a degradation-prone layer ('template layer') and a degradation-resistant layer ('resistant layer'). This pattern of secondary cell wall formation in the water-conducting cells of extant vascular plants matches the pattern of wall thickenings in the tracheids of early fossil vascular plants and provides a key evolutionary link between tracheids of living vascular plants and those of their earliest fossil ancestors. Further studies of tracheid development and structure among basal extant vascular plants will lead to a more precise reconstruction of the early evolution of water-conducting tissues in land plants, and will add to the current limited knowledge of spatial, temporal and cytochemical aspects of cell wall formation in tracheary elements of vascular plants.

Biological Evolution↗
PubMed2000

The evolution of C4 plants: acquisition of cis-regulatory sequences in the promoter of C4-type pyruvate, orthophosphate dikinase gene.

In a previous study, we identified the C4-like pyruvate, orthophosphate dikinase gene (Pdk) in the C3 plant rice, with a similar structure to the C4-type Pdk in the C4 plant maize. In order to elucidate the differences between C4-type and C4-like Pdk genes in C4 and C3 plants, we have produced chimeric constructs with the beta-glucuronidase (GUS) reporter gene under the control of the Pdk promoters. In transgenic rice, both rice and maize promoters directed GUS expression in photosynthetic organs in a light-dependent manner. However, the maize promoter exhibited a much higher transcriptional activity than the rice promoter did. These results indicate that the rice C4-like Pdk gene resembles the maize C4-type Pdk gene in terms of regulation of expression. We also tested the activity of the rice promoter in transgenic maize. GUS activity was seen in both photosynthetic and non-photosynthetic organs. Thus, the rice promoter does not confer a strict organ-specific gene expression, as the maize promoter does. Moreover, the rice promoter directed GUS expression not only in mesophyll cells but also in bundle sheath cells, whereas the maize promoter directed expression only in mesophyll cells. Taken together, the results obtained from both transgenic maize and rice demonstrate that the rice and maize promoters differ not only quantitatively, but also qualitatively, in terms of their cell- and organ-specificity. Experiments with swapped promoters using the rice and maize promoters further demonstrated that a limited sequence region from -330 to -76 of the maize promoter confers light-regulated, high-level expression to the rice promoter in maize mesophyll protoplasts. We conclude the gain of cis-acting elements conferring high-level expression and mesophyll cell specificity was necessary for establishment of a C4-type Pdk gene during the course of evolution from C3 to C4 plants.

Evolution, Molecular↗
PubMed1999

Endosymbiosis and evolution of the plant cell.

The bacterial origins of plastid division and protein import by plastids are beginning to emerge - thanks largely to the availability of a total genome sequence for a cyanobacterium. Despite existing for hundreds of millions of years within the plant cell host, the chloroplast endosymbiont retains clear hallmarks of its bacterial ancestry. Plastid division relies on proteins that are also responsible for bacterial division, although may of the genes for these proteins have been confiscated by the host. Plastid protein import on the other hand relies on proteins that seem to have functioned originally as exporters but that have now been persuaded to operate in the reverse direction to traffic proteins from the host cell into the endosymbiont.

Chloroplasts↗
PubMed2003

The co-evolution of people, plants, and parasites: biological and cultural adaptations to malaria.

The urgency generated by drug-resistant strains of malaria has accelerated anti-malarial drug research over the last two decades. While synthetic pharmaceutical agents continue to dominate research, attention increasingly has been directed to natural products. The present paper explores the larger context in which plant use occurs and considers how the selection of medicinal plants has evolved over millennia as part of the larger human effort to mediate illness. First attention is directed to indigenous medicinal plants whose anti-malarial activity is based on an oxidant mode of action, by which intracellular constituents lose electrons (become more electropositive). Next, parallels are drawn between these plant substances and a suite of malaria-protective genetic traits: glucose-6-phosphate dehydrogenase deficiency; haemoglobins S, C and E; alpha- and beta-thalassemias. These erythrocyte anomalies are classic examples of Darwinian evolution, occurring in high frequency in populations who have experienced considerable selective pressure from malaria. Characterized by discrete loci and pathophysiologies, they are united through the phenomenon of increased erythrocyte oxidation. In this model, then, oxidant anti-malarial plants are culturally constructed analogues, and molecular mimics, of these genetic adaptations. To further reinforce the scheme, it is noted that the anti-malarial action of pharmaceutical agents such as chloroquine and mefloquine duplicates both the genetic anomalies and the folk therapeutic models based in oxidant plants. This discussion coheres around a theoretical foundation that relates plant secondary metabolites (oxidants) to plasmodial biochemistry and human biological and cultural adaptations to malaria. Co-evolution provides a theoretical link that illuminates how medical cultures manage the relationships among humans, plants, herbivores and their respective pathogens.

Adaptation, Physiological↗
PubMed2000

Grazing optimization, nutrient cycling, and spatial heterogeneity of plant-herbivore interactions: should a palatable plant evolve?

Can the evolution of plant defense lead to an optimal primary production? In a general theoretical model, Loreau (1995) and de Mazancourt et al. (1998, 1999) have shown that herbivory could increase primary production up to a moderate rate of grazing intensity through recycling of a limiting nutrient, provided several conditions are fulfilled. In the present paper, we assume: (1) grazing intensity is controlled by plants through their level of palatability; and (2) plant fitness is determined by its productivity. We explore the conditions under which such an optimal production may be reached through natural selection. We model two competing plant types that differ only in palatability and are distributed in a patchy landscape determined by the plant-herbivore interaction. Patch size is determined by herbivore behavior: herbivores recycle nutrient homogeneously within patches, but recycle nutrient proportionally to consumption between patches. The model shows that a strategy of intermediate palatability can be adaptive in response to a small herbivore that lives on and recycles nutrient around one or a few individual plants. For moderately small herbivores, plant palatability may evolve towards one of two local convergent strategies, depending on the initial conditions. For medium- to large-sized herbivores, the nonpalatable strategy is always selected. We discuss the functional and evolutionary implications of these results, and suggest that the traditional dichotomy describing antagonistic and mutualistic interactions may be misleading.

Adaptation, Physiological↗
PubMed1992

Green algae and the evolution of land plants: inferences from nuclear-encoded rRNA gene sequences.

Phylogenetic analysis of 381 informative sites in partial sequences of nuclear-encoded large and small subunit ribosomal RNAs from 38 chlorophyll a- and b-containing plants (Chlorobionta sensu Bremer) including tracheophytes, bryophytes, charophytes and chlorophytes, supports the hypotheses of: (1) monophyly of the green plants (excluding Euglenophyta); (2) monophyly of the embryophytes; (3) non-monophyly of the bryophytes; (4) monophyly of the tracheophytes; and (5) a single origin of embryophytes from charophycean green algae. The Charales and Klebsormidium appear to be the green algae most closely related to the land plants. The unexpected basal divergence of Coleochaete and the apparent non-monophyly of the Zygnematales are not robustly supported and, thus, are interpreted to be sources of new questions, rather than new phylogenetic hypotheses.

Biological Evolution↗
PubMed1992

Carnivorous plants: phylogeny and structural evolution.

The carnivorous habit in flowering plants represents a grade of structural organization. Different morphological features associated with the attraction, trapping, and digestion of prey characterize a diversity of specialized forms, including the familiar pitcher and flypaper traps. Phylogenetic analysis of nucleotide sequence data from the plastic rbcL gene indicates that both carnivory and stereotyped trap forms have arisen independently in different lineages of angiosperms. Furthermore, these results demonstrate that flypaper traps share close common ancestry with all other trap forms. Recognition of these patterns of diversification may provide ideal, naturally occurring systems for studies of developmental processes underlying macromorphological evolution in angiosperms.

Base Sequence↗
PubMedDate not supplied

[Plant life evoluton: opinions and suppositions].

Evolution of plant life has been considered in the context of phylembryogenesis or heterochronia. Hewever, suggested opinions and suppositions regarding the mechanisms, direction and rate of evolutionary changes are opposite. Concepts of phylembryogenesis and heterochronia originally were developed for the different levels of organization and could be distinguished by different modes of morphological evolution. In this connection, interpretations of evolutional changes of shoots morphogenesis, ontogenesis and plant habitus by different types of heterochronia and modes of phylembryogenesis were delineated. It was proposed that evolution of plants life forms could be considered regarding functional specialization of root-shoot (the basic element of life form structure) that appears as metamorphoses of bud, root and shoot. Evolutional changes of root-shoot could take places at the different stages of development due to anabolies (modifications). At the same time epigenetic and episelectional (organic selection) mechanisms of evolution play an important role in the evolution of plant life forms. Moreover, results of modern genetic and molecular phylogenetic investigations produce evidences for the saltations and reversions in the plant life forms evolution.

Biological Evolution↗
PubMed1998

Evolution of the plant mitochondrial genome: dynamics of duplication and deletion of sequences.

Several descriptive models have been proposed to explain the occurrence of deletion-duplication events in the plant mitochondrial genome. In order to investigate the dynamics of these events, we have simulated them using a computer model. The simulation shows that whatever the recombination rates between repeats, if a mitochondrial sequence becomes unnecessary for the proper function of mitochondria, this sequence can be deleted and another sequence can be duplicated in consequence. Furthermore, the model shows that the organization of the sequences with respect to the origin of replication has a great influence over the dynamics of the deletion-duplication events.

DNA, Mitochondrial↗
PubMed2003

Mutational bias affects protein evolution in flowering plants.

Amino acid sequences from several thousand homologous gene pairs were compared for two plant genomes, Oryza sativa and Arabidopsis thaliana. The Arabidopsis genes all have similar G+C (guanine plus cytosine) contents, whereas their homologs in rice span a wide range of G+C levels. The results show that those rice genes that display increased divergence in their nucleotide composition (specifically, increased G+C content) showed a corresponding, predictable change in the amino acid compositions of the encoded proteins relative to their Arabidopsis homologs. This trend was not seen in a "control" set of rice genes that had nucleotide contents closer to their Arabidopsis homologs. In addition to showing an overall difference in the amino acid composition of the homologous proteins, we were also able to investigate the biased patterns of amino acid substitution since the divergence of these two species. We found that the amino acid exchange matrix was highly asymmetric when comparing the High G+C rice genes with their Arabidopsis homologs. Finally, we investigated the possible causes of this biased pattern of sequence evolution. Our results indicate that the biased pattern of protein evolution is the consequence, rather than the cause, of the corresponding changes in nucleotide content. In fact, there is an even more marked asymmetry in the patterns of substitution at synonymous nucleotide sites. Surprisingly, there is a very strong negative correlation between the level of nucleotide bias and the length of the coding sequences within the rice genome. This difference in gene length may provide important clues about the underlying mechanisms.

Amino Acids↗
PubMed2006

Evolution of talking plants in a tritrophic context: conditions for uninfested plants to attract predators prior to herbivore attack.

Herbivory induces plants to emit volatile chemicals that attract enemies of the herbivores (bodyguards of plants). In this way, the plant acquires protection and the bodyguards gain food. These plant signals cause neighboring plants, not under attack, to release signals as well. We hypothesize that such "secondary" signals help to reduce damage from future herbivore attacks by the protection received from the bodyguards. By modeling we explore the conditions for such secondary signals to evolve. Three kinds of strategies are considered: plants of the first strategy always emit a signal, those of the second strategy emit a signal only when infested, and those of the third strategy emit a signal not only when infested, but also when a certain number of neighbors are infested (i.e. secondary signaling). When signaling is much less (much more) costly than damage from herbivory, the first (second) strategy will be favored by selection, whereas for intermediate costs the third strategy, i.e. secondary signaling, will evolve. However, secondary signaling will not evolve when the primary signals lure the bodyguards too effectively. This is because the undamaged plant gains associational defense when the infested individual is defending very well; therefore, the need for secondary signaling decreases.

Animals↗