Transposable elements (TEs) usually represent the most abundant and dynamic fraction of genomes in almost all living organisms. The overall capacity of such 'junk DNA' to induce mutations and foster the reorganization of functional genomes suggests that TE may be of central evolutionary significance. However, to what extent TE dynamics drive and is driven by the evolutionary trajectory of host taxa remains poorly known. Further work addressing the fate of TE insertions in natural populations is necessary to shed light on their impact on microevolutionary processes. Here, we highlight methodological approaches (i.e. transposon displays and high-throughput sequencing), tracking TE insertions across large numbers of individuals and discuss their pitfalls and benefits for molecular ecology surveys.

Nepeta nuda (catmint; Lamiaceae) is a perennial medicinal plant with a wide geographic distribution in Europe and Asia. This study first characterized the taxonomic position of N. nuda using DNA barcoding technology. Since medicinal plants are rich in secondary metabolites contributing to their adaptive immune response, we explored the N. nuda metabolic adjustment operating under variable environments. Through comparative analysis of wild-grown and in vitro cultivated plants, we assessed the change in phenolic and iridoid compounds, and the associated immune activities. The wild-grown plants from different Bulgarian locations contained variable amounts of phenolic compounds manifested by a general increase in flowers, as compared to leaves, while a strong reduction was observed in the in vitro plants. A similar trend was noted for the antioxidant and anti-herpesvirus activity of the extracts. The antimicrobial potential, however, was very similar, regardless the growth conditions. Analysis of the N. nuda extracts led to identification of 63 compounds including phenolic acids and derivatives, flavonoids, and iridoids. Quantification of the content of 21 target compounds indicated their general reduction in the extracts from in vitro plants, and only the ferulic acid (FA) was specifically increased. Cultivation of in vitro plants under different light quality and intensity indicated that these variable light conditions altered the content of bioactive compounds, such as aesculin, FA, rosmarinic acid, cirsimaritin, naringenin, rutin, isoquercetin, epideoxyloganic acid, chlorogenic acid. Thus, this study generated novel information on the regulation of N. nuda productivity using light and other cultivation conditions, which could be exploited for biotechnological purposes.

Transposable elements (TE) can constitute a large fraction of plant genomes, yet our understanding of their evolution and fitness effect is still limited. Here we tested several models of evolution that make specific predictions about differences in TE abundance between selfing and outcrossing taxa, and between small and large populations. We estimated TE abundance in multiple populations of North American Arabidopsis lyrata differing in mating system and long-term size, using transposon insertion display on several TE families. Selfing populations had higher TE copy numbers per individual and higher TE allele frequencies, supporting models which assume that selection against TEs acts predominantly against heterozygotes via the process of ectopic recombination. In outcrossing populations differing in long-term size, the data supported neither a model of density-regulated transposition nor a model of direct deleterious effect. Instead, the population structure of TEs revealed that outcrossing populations tended to split into western and eastern groups - as previously detected using microsatellite markers - whereas selfing populations from west and east were less differentiated. This, too, agrees with the model of ectopic recombination. Overall, our results suggest that TE elements are nearly neutral except for their deleterious potential to disturb meiosis in the heterozygous state.

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Transposable elements usually comprise the most abundant nongenic fraction of eukaryotic genomes. Because of their capacity to selfreplicate and to induce a wide range of mutations, transposable elements have long been considered as 'parasitic' or 'selfish'. Today, we recognize that the findings about genomic changes affected by transposable elements have considerably altered our view of the ways in which genomes evolve and work. Numerous studies have provided evidences that mobile elements have the potential to act as agents of evolution by increasing, rearranging and diversifying the genetic repertoire of their hosts. With large-scale sequencing becoming increasingly available, more and more scientists come across transposable element sequences in their data. I will provide examples that transposable elements, although having signatures of 'selfish' DNA, play a significant biological role in the maintainance of genome integrity and providing novel regulatoty networks. These features, along with the transpositional and mutagenic capacity to produce a raw genetic diversity, make the genome mobile fraction, a key player in species adaptation and microevolution. The last but not least, transposable elements stand as informative DNA markers that may complement other conventional DNA markers. Altogether, transposable elements represent a promising, but still largely unexplored research niche and deserve to be included into the agenda of molecular ecologists, evolutionary geneticists, conservation biologists and plant breeders.

Abstract:The bulk of large plant genomes consists of retrotransposons. Retrotransposons are able to integrate into a multitude of loci in the genome, and can thereby generate insertional polymorphism between individuals, as well as mutations and new characteristics. Retrotransposons are largely quiescent during development, but become more active in response to biotic and abiotic stresses, which cause them to produce larger pools of transcripts. The present study assesses the structural dynamics and putative transcriptional activation of BARE-1 and WIS 2-1A retrotransposons in ethyl methanesulfonate (EMS)-induced hexaploid wheat and Triticale sphaerococcum mutants, via an RT-PCR approach that utilized the retrotransposon based markers SSAP, IRAP and REMAP. Our results demonstrate a polymorphic pattern distribution of BARE-1/WIS 2-1A members, and identify new insertions. The WIS 2-1A retrotransposon members have a modulated transcriptional profile, which strongly suggests that EMS treatment encourages their activation Retrotransposon-based methods are efficient for fingerprinting and genetic polymorphism studies of sphaerococcum mutant forms, and can illuminate the genome dynamics affecting the genes responsible for the sphaerococcum phenotype.

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The maintenance of plant genome integrity plays a critical function in the processes of DNA replication, transcription, and repair. Short-wave UV radiation (UVC) is among the most harmful agents known to affect genome stability and to induce DNA damage, including double-strand breaks (DSBs). Most previous studies in plants addressed the effects of UVC radiation at the physiological level; however, little research effort has been put into genome sensitivity across different plant species. Here, we made use of the trypan blue exclusion test and neutral comet assay to assess nuclear membrane and genome integrity in response to UVC radiation in monocot and dicot plants. We found that UVC radiation substantially affects nuclear membranes and the level of DSBs in a dose-responsive manner. Furthermore, differential sensitivity across plant species was observed, with monocot plants being less vulnerable to DSBs. This allows us to speculate that plant species with larger genomes may better tolerate UVC radiation.