Plant growth-promoting rhizobacteria: Beneficial bacteria that enhance plant growth and biomass production and live in association with plant roots in natural environments. Synanthropy: Occurrence of an organism in association with human settlement, where human activities directly or indirectly generate favorable environmental conditions for the organism. Ultramafic soils: Infertile, nutrient poor soils derived from so-called serpentine minerals, which are common in zones of tectonic activity.
The popularity of A. The ease and speed with which experiments can be conducted on A. The many uses of Arabidopsis as the universal reference plant continue to expand, particularly in the field of systems biology Brady et al. Many of the traits that render A.
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Indeed, the natural history of A. Within these six evolutionary lineages, a number of phylogenetically as yet unresolved taxa have been described, as have auto- and allopolyploidization events see Glossary. The divergence time of the common ancestor of these species and the A.
Thus, divergence occurred immediately before or during the transition from a warm period to progressively colder climates, followed by rapid glacial cycles from 3 Mya until the latest glacial maximum about 18, years ago. There has even been a natural allopolyploidization event between A.
From left to right: A. The individuals shown here do not reflect the large within-species morphological diversity, particularly in leaf shape, among different accessions of A. Work in recent years has increasingly emphasized the relevance of conducting experiments on A. This important development will benefit from a more detailed knowledge of the unique and shared features of its natural and evolutionary history, as well as of the natural environments that host populations of A.
Arabidopsis thaliana is recognized as native to Western Eurasia Figure 3. The species is a colonizer and pioneer plant of disturbed, poor, stony or shallow soils, and it can also be found in nutrient-poor, often sandy, meadow and forest habitats Mitchell-Olds and Schmitt, Similarly, the species closely related to A. Sequence polymorphism data provide evidence for a historical expansion of the A. It has been suggested that A. There is also clear evidence for additional glacial refugia for A.
This reflects an evolutionary history of vast climatic and environmental fluctuations, likely including a series of alternating phases of population size contraction and expansion with migration and admixture following glacial cycles Beck et al. In the past few years, A. The present climatic and geographic range of A. Areas colored in red correspond to the continuous distribution of A. This map is based on a partial map kindly provided by Matthias Hoffmann personal communication, November , with manual additions to the southern hemisphere Bresinsky et al.
In addition to—and likely permitting—the rapid expansion of its range, A.
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Estimates place these transitions as having occurred, based on different approaches, at around 0. By contrast, most species closely related to A. In addition to selfing, A. Vegetative A. The leaves of A. These morphological differences are likely to constitute adaptations to differing environments. By comparison to its sister group of species, the flowering of A. Seeds of A. These features of A.
The complexity of organ architecture appears to be reduced in A. Notably, its roots mostly contain only a single layer of each specialized cell type, a feature that is optimal for in vivo imaging Figure 4 De Lucas and Brady, This organization differs from the roots of its close relative A.
The metabolic cost of building an A. Longitudinal left and transverse right confocal sections of A. Green fluorescence highlights the plasma membrane of the pericycle cells of an A. Red fluorescence of propidium iodide PI as a stain is overlaid to visualize cell walls. The root cell layers consecutive outward to inward are: epidermis e , cortex c , endodermis n and pericycle p. Note that the Casparian Strip surrounding the endodermis cells forms an apoplastic diffusion barrier Roppolo et al.
By comparison, the genome of the diploid A. This is associated with a pronounced reduction in genome size in A. For comparison, nuclear genome sizes of its closest relatives are larger, mostly due to a higher abundance of transposable elements in euchromatic regions, with Mbp for the reference assembly of the nuclear genome of A. These properties of A. All of these characteristic features of A.
Classical molecular genetics approaches have been used in A. These stem cells fuel the ongoing indeterminate growth that is characteristic of plants Clark et al. The biology of A.
Specialisation Organismal Adaptation and Development
Important work has investigated the molecular networks that mediate environmentally controlled developmental switches in A. Examples include the light-regulated development of seedlings photomorphogenesis Deng et al. The need for developmental transitions to be timed accurately and robustly is reflected in the emerging complex, multi-layered epigenetic regulation of some key loci, for example the flowering control gene Flowering Locus C FLC Simpson and Dean, ; Csorba et al.
Such complex regulation in A. In the near future, there will be a wealth of new information on each of these questions. We only have a rudimentary understanding of which traits are most important, and the numbers of genes controlling each of these traits is large. Therefore, the most thorough and objective approach would be to associate genes with phenotypes by scanning the entire genome, presumably with single nucleotide polymorphism SNP markers.
Linking Ecology, Molecular Biology and Bioinformatics in plant epigenetic research
The practical difficulties of this approach, however, are enormous. How are these candidates chosen? The most obvious approach is to choose genes based on their known function — either in the plant of interest or in other species. Of course, it is best if the candidates have been directly tested in the species of interest.
Bradshaw's data and physiological model suggest that mutations in this gene might be involved in the adaptation of a wide variety of natural plant populations to serpentine soils. This requires a comparative analysis of naturally occurring alleles within a single species, or orthologous loci in sister taxa, perhaps using transgenic approaches Bradshaw. Candidate genes can also be identified based on their positions on quantitative trait locus QTL maps or patterns of gene expression.
One way to do this is to characterize variation in neutral genetic markers. The microsatellite markers and sampling strategies described by Cole pp. Although all angiosperms and most land plants may be polyploid, the number, antiquity and types of genome duplications and subsequent genome reorganizations vary among taxa Soltis, The mechanisms that direct the evolutionary fate of duplicated genes are still unclear.
Is this a common pattern in plants? With the rice and poplar genome sequences in hand, and other plant genome sequences on the horizon, we can begin to answer these questions. Based on synonymous nucleotide substitution rates, the authors estimated that the duplication occurred 8—13 Myr ago, which conflicts with fossil evidence that suggests that the species diverged 18—58 Myr ago Eckenwalder, When an inbred variety of flax P1 is grown in an inducing environment, it gives rise to progeny called genotrophs that exhibit stable changes in size, branching, seed hairs, isozymes, hormone levels, nuclear DNA contents, number of ribosomal genes and number of other repetitive sequences.
Although the parents remain phenotypically plastic when grown in different environments, the altered phenotypes of the genotrophs are stable. This feature issue illustrates that we are at an exciting and challenging crossroads in the study of plant adaptation. A powerful suite of tools is now available for Arabidopsis , and other taxa that are highly divergent with respect to evolutionary distance rice and perennial growth habit poplar.
Moreover, genomic resources are becoming increasingly available for other tree species and plants that are models of adaptive evolution. Perhaps the most difficult challenge is not the development of tools and resources, but the complete merging of genomic, ecological and evolutionary perspectives. Volume , Issue 1. I agree to help cultivate an open and respectful discussion. This comment form is under antispam protection. Notify of. Get our newsletter.