Miniature Inverted-repeat Elements Research Articles

The distribution of transposable elements (TEs) in the promoter regions of moso bamboo genes and its influence on downstream genes

Transposable elements are abundant in the promoter regions of moso bamboo genome and influence the expression of downstream genes. As important components of animal and plant genomes, transposable elements (TEs) can shape host genomes and regulate gene expression. In the present study, TEs distributed in the promoter regions of moso bamboo genome were systematically investigated with stringy parameters using RepeatMasker. Approximately 85.7% of the promoter regions were anchored into the TE sequences. Among TE families, three types of TEs are preferentially inserted into the promoter regions: hAT-like transposons, miniature inverted-repeat elements (MITEs), and short interspersed elements (SINEs). The TE insertion sites in promoter regions were amplified by PCR. One site (TE-20) exhibited insertion polymorphism. The expression of downstream gene PH01003704G0280 was three to five times higher with the absence of TE-20 than with the presence of it. On the basis of previous studies it was hypothesized that TEs distributed in the promoter regions of four homologs of floral pathway integrators (FPIs) might be responsible for the observed low expression level. To test the hypothesis, four promoter sequences with TE insertions and TE deletions were inserted upstream of the open reading frame of the β-glucuronidase (GUS) gene and green fluorescent protein (GFP) reporter genes. The expression level of downstream genes was higher with TE deletions than with TE insertions. These results show that the TEs are abundant in the promoter regions and influence the expression of downstream genes in moso bamboo genome.

Production of plasmid-encoding NDM-1 in clinical Raoultella ornithinolytica and Leclercia adecarboxylata from China.

Raoultella ornithinolytica YNKP001 and Leclercia adecarboxylata P10164, which harbor conjugative plasmids pYNKP001-NDM and pP10164-NDM, respectively, were isolated from two different Chinese patients, and their complete nucleotide sequences were determined. Production of NDM-1 enzyme by these plasmids accounts for the carbapenem resistance of these two strains. This is the first report of blaNDM in L. adecarboxylata and third report of this gene in R. ornithinolytica. pYNKP001-NDM is very similar to the IncN2 NDM-1-encoding plasmids pTR3, pNDM-ECS01, and p271A, whereas pP10164-NDM is similar to the IncFIIY blaNDM-1-carrying plasmid pKOX_NDM1. The blaNDM-1 genes of pYNKP001-NDM and pP10164-NDM are embedded in Tn125-like elements, which represent two distinct truncated versions of the NDM-1-encoding Tn125 prototype observed in pNDM-BJ01. Flanking of these two Tn125-like elements by miniature inverted repeat element (MITE) or its remnant indicates that MITE facilitates transposition and mobilization of blaNDM-1 gene contexts.

High throughput sequencing reveals novel and abiotic stress-regulated microRNAs in the inflorescences of rice

BackgroundMicroRNAs (miRNAs) are small RNA molecules that play important regulatory roles in plant development and stress responses. Identification of stress-regulated miRNAs is crucial for understanding how plants respond to environmental stimuli. Abiotic stresses are one of the major factors that limit crop growth and yield. Whereas abiotic stress-regulated miRNAs have been identified in vegetative tissues in several plants, they are not well studied in reproductive tissues such as inflorescences.ResultsWe used Illumina deep sequencing technology to sequence four small RNA libraries that were constructed from the inflorescences of rice plants that were grown under control condition and drought, cold, or salt stress. We identified 227 miRNAs that belong to 127 families, including 70 miRNAs that are not present in the miRBase. We validated 62 miRNAs (including 10 novel miRNAs) using published small RNA expression data in DCL1, DCL3, and RDR2 RNAi lines and confirmed 210 targets from 86 miRNAs using published degradome data. By comparing the expression levels of miRNAs, we identified 18, 15, and 10 miRNAs that were regulated by drought, cold and salt stress conditions, respectively. In addition, we identified 80 candidate miRNAs that originated from transposable elements or repeats, especially miniature inverted-repeat elements (MITEs).ConclusionWe discovered novel miRNAs and stress-regulated miRNAs that may play critical roles in stress response in rice inflorescences. Transposable elements or repeats, especially MITEs, are rich sources for miRNA origination.

Diversity of DcMaster-like elements of the PIF/Harbinger superfamily in the carrot genome

Transposable elements constitute a significant fraction of plant genomes. Both autonomous and non-autonomous elements of the DcMaster family, residing in the carrot genome, were described previously. DcMaster elements were classified as members of the PIF/Harbinger superfamily. In the present paper we report on the identification of other groups of DcMaster-like elements. Beside the previously described, relatively highly abundant miniature inverted repeat element (MITE) family Krak (ca. 3,600 copies, ca. 80% intra-family similarity), three other families, i.e. 1.1 kb long KrakL1 (ca. 3,000 copies, ca. 98% intra-family similarity), 1.2 kb long KrakL2 (a single identified element, 71.1% similar to KrakL1 consensus), and 2.2 kb long Midi (few elements, 99% intra-family similarity), were revealed. The fact that all members within each of the newly found families were almost identical in their sequence suggests their very recent activity. The families differed in terms of their similarity to the canonical DcMaster element. They also differed in copy number, from just a few copies of Midi to few thousand copies of Krak. A modification of the DcMaster Transposon Display (DcMTD) marker system, targeted specifically towards Krak elements, was used to investigate their insertion polymorphism. It was shown that Krak insertion sites, similarly to those of the DcMaster elements, were highly polymorphic between the wild and the cultivated Daucus carota.

Diversity and structure of PIF/Harbinger-like elements in the genome of Medicago truncatula

BackgroundTransposable elements constitute a significant fraction of plant genomes. The PIF/Harbinger superfamily includes DNA transposons (class II elements) carrying terminal inverted repeats and producing a 3 bp target site duplication upon insertion. The presence of an ORF coding for the DDE/DDD transposase, required for transposition, is characteristic for the autonomous PIF/Harbinger-like elements. Based on the above features, PIF/Harbinger-like elements were identified in several plant genomes and divided into several evolutionary lineages. Availability of a significant portion of Medicago truncatula genomic sequence allowed for mining PIF/Harbinger-like elements, starting from a single previously described element MtMaster.ResultsTwenty two putative autonomous, i.e. carrying an ORF coding for TPase and complete terminal inverted repeats, and 67 non-autonomous PIF/Harbinger-like elements were found in the genome of M. truncatula. They were divided into five families, MtPH-A5, MtPH-A6, MtPH-D,MtPH-E, and MtPH-M, corresponding to three previously identified and two new lineages. The largest families, MtPH-A6 and MtPH-M were further divided into four and three subfamilies, respectively. Non-autonomous elements were usually direct deletion derivatives of the putative autonomous element, however other types of rearrangements, including inversions and nested insertions were also observed. An interesting structural characteristic – the presence of 60 bp tandem repeats – was observed in a group of elements of subfamily MtPH-A6-4. Some families could be related to miniature inverted repeat elements (MITEs). The presence of empty loci (RESites), paralogous to those flanking the identified transposable elements, both autonomous and non-autonomous, as well as the presence of transposon insertion related size polymorphisms, confirmed that some of the mined elements were capable for transposition.ConclusionThe population of PIF/Harbinger-like elements in the genome of M. truncatula is diverse. A detailed intra-family comparison of the elements' structure proved that they proliferated in the genome generally following the model of abortive gap repair. However, the presence of tandem repeats facilitated more pronounced rearrangements of the element internal regions. The insertion polymorphism of the MtPH elements and related MITE families in different populations of M. truncatula, if further confirmed experimentally, could be used as a source of molecular markers complementary to other marker systems.

Mobile elements in archaeal genomes

The recent availability of several archaeal genome sequences has provided a basis for detailed analyses of the frequency, location and phylogeny of archaeal mobile elements. All the known elements fall into two main types, autonomous insertion sequence (IS) elements and the non-autonomous miniature inverted repeat element (MITE)-like elements. Both classes are considered to be mobilized via transposases that are encoded by the IS elements, although mobility has only been demonstrated experimentally for a few elements. The number, and diversity, of the elements differs greatly between the genomes. At one extreme Sulfolobus solfataricus P2 and Halobacterium NRC-1 are very rich in elements while Methanobacterium thermoautotrophicum contains none. The former also show examples of complex clusters of interwoven elements. An analysis of the genomic distribution in S. solfataricus suggests that the putative oriC and terC regions act as barriers for the mobility of both IS and MITE-like elements. Moreover, the very high level of truncated IS elements in the genomes of S. solfataricus, Sulfolobus tokodaii and Thermoplasma volcanium suggests that there may be a cellular mechanism for selectively inactivating IS elements at a point when they become too numerous and disadvantageous for the cell. Phylogenetically, archaeal IS elements are confined to 11 of the 17 known families of bacterial and eukaryal IS elements where some generate distinct subgroups. Finally, DNA viruses, plasmids and DNA fragments can also be inserted into, and excised from, archaeal genomes by means of an integrase-mediated mechanism that has special archaeal characteristics.

Mobile elements in archaeal genomes

The recent availability of several archaeal genome sequences has provided a basis for detailed analyses of the frequency, location and phylogeny of archaeal mobile elements. All the known elements fall into two main types, autonomous insertion sequence (IS) elements and the non-autonomous miniature inverted repeat element (MITE)-like elements. Both classes are considered to be mobilized via transposases that are encoded by the IS elements, although mobility has only been demonstrated experimentally for a few elements. The number, and diversity, of the elements differs greatly between the genomes. At one extreme Sulfolobus solfataricus P2 and Halobacterium NRC-1 are very rich in elements while Methanobacterium thermoautotrophicum contains none. The former also show examples of complex clusters of interwoven elements. An analysis of the genomic distribution in S. solfataricus suggests that the putative oriC and terC regions act as barriers for the mobility of both IS and MITE-like elements. Moreover, the very high level of truncated IS elements in the genomes of S. solfataricus, Sulfolobus tokodaii and Thermoplasma volcanium suggests that there may be a cellular mechanism for selectively inactivating IS elements at a point when they become too numerous and disadvantageous for the cell. Phylogenetically, archaeal IS elements are confined to 11 of the 17 known families of bacterial and eukaryal IS elements where some generate distinct subgroups. Finally, DNA viruses, plasmids and DNA fragments can also be inserted into, and excised from, archaeal genomes by means of an integrase-mediated mechanism that has special archaeal characteristics.

Standing on the shoulders of giants

Few scientists have had a greater impact on our understanding of biological processes than Barbara McClintock. Her discovery of transposable elements and her unorthodox ideas about genome organization and function have provided the intellectual foundation for the current genomics revolution.Using genomics technology, Jeff Bennetzen (Purdue University, West Lafayette, USA) has begun to develop a comprehensive view of the prevalance and distribution of transposable elements in maize and the distantly related grasses, rice and sorghum. In 1996, Bennetzen's lab made the surprising discovery that most of the huge stretches of intergenic DNA in maize are comprised exclusively of one class of element, retrotransposons that can apparently attain phenomenal copy numbers by inserting harmlessly into each other. The ability to date retrotransposon insertion times through the divergence of the long terminal repeat (LTR) sequences of the elements led to another surprising finding, that most retrotransposition has occurred within the past five million years.The idea that the transposable elements in the maize genome have undergone recent and massive amplification is also consistent with the findings of Qiang Zhang (University of Georgia, Athens, USA) who reported on the Heartbreaker (Hbr) family of miniature inverted repeat elements (MITEs). The finding that the 3000 to 4000 Hbr elements are both highly conserved (<90%) and polymorphic in maize suggests that they have recently been amplified. Zhang also reported that over 70% of the examined Hbr insertion sites were in single or low copy sequences (regions thought to contain the genes), despite 80–90% of the maize genome being repetitive. Taken together, the data on the recent amplification of retrotransposons and MITEs indicate that the maize genome has a very dynamic recent history, and this may have contributed to its remarkable success as an easily adaptable crop plant.This meeting described the use of genes isolated from Antirrhinum to yeast to explore maize biology. As the era of functional genomics and interspecific investigations advances, exciting new challenges and opportunities await this generation of maize geneticists.