1,720,972 research outputs found
Retrotransposon-related genetic distance and hybrid performance in sunflower (Helianthus annuus L.)
No full textHeterosis is a main force leading the development of the hybrid seed industry in sunflower. The purpose of this study is to evaluate if heterosis effects for morphological traits among sunflower hybrids can be related to differences in the repetitive component of the genome of parental lines. The assumption is that, at least for certain traits, heterosis results from mutations in the cis-regulatory elements of genes, largely related to retrotransposon insertions and/or removals. Our experimental approach consists of a correlation study between hybrid performance and retrotransposon-related genetic distances between inbreds. Six sunflower inbred lines of different origin were crossed in a half diallel fashion; comparing parental lines and hybrids, mid parent heterosis of F1 hybrids was evaluated for six traits. We estimated the parental genetic distances between the six inbreds on data gathered by the inter-retrotransposon-amplified polymorphism (IRAP) protocol. Different retrotransposons previously isolated in sunflower were targeted by 11 primer pairs designed on conserved LTR domains. As a control, genetic distances were also calculated using 86 genic SNPs. We analysed the correlation between the mid-parent heterosis for each of the six traits analysed and the genetic distance (calculated on data obtained by SNP or IRAP analyses) between the parental lines. Differences between parents showed to be largely related to variations in the retrotransposon component of the genome. Retrotransposon-related genetic distance between parents resulted to be larger than that related to genic SNPs, and significantly correlated to seed yield and, at a lesser extent, to plant height and stem diameter in hybrids. The hypothesis that variations in the repetitive component of the genome, especially LTR-retrotransposons, affect the displaying of heterosis is discussed
Large Retrotransposon-Related Variability in Helianthus annuus Wild Accessions and in the Helianthus Genus.
No full text
Characterization of HaCRE1, a complete Copia retrotransposon of sunflower (Helianthus annuus L.).
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
HACRE1, a recently inserted copia-like retrotransposon of sunflower (Helianthus annuus L.)
No full textn this paper we report on the isolation and characterization, for the first time, of a complete 6511 bp retrotransposon of sunflower. Considering its protein domain order and sequence similarity to other copia elements of dicotyledons, this retrotransposon was assigned to the copia retrotransposon superfamily and named HACRE1 (Helianthus annuus copia-like retroelement 1). HACRE1 carries 5′ and 3′ long terminal repeats (LTRs) flanking an internal region of 4661 bp. The LTRs are identical in their sequence except for two deletions of 7 and 5 nucleotides in the 5′ LTR. Based on the sequence identity of the LTRs, HACRE1 was estimated to have inserted within the last 84 000 years. The isolated sequence contains a complete open reading frame with only one complete reading frame. The absence of nonsense mutations agrees with the very high sequence identity between LTRs, confirming that HACRE1 insertion is recent. The haploid genome of sunflower (inbred line HCM) contains about 160 copies of HACRE1. This retrotransposon is expressed in leaflets from 7-day-old plantlets under different light conditions, probably in relation to the occurrence of many putative light-related regulatory cis-elements in the LTRs. However, sequenced cDNAs show less variability than HACRE1 genomic sequences, indicating that only a subset of this family is expressed under these conditions
Characterization of HACRE1, a complete Copia retrotransposon of sunflower (Helianthus annuus L.)
No full textCharacterization of HACRE1, a complete Copia retrotransposon of sunflower (Helianthus annuus L.)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
<it>Copia </it>and <it>Gypsy </it>retrotransposons activity in sunflower (<it>Helianthus annuus </it>L.)
Full text linkAbstract Background Retrotransposons are heterogeneous sequences, widespread in eukaryotic genomes, which refer to the so-called mobile DNA. They resemble retroviruses, both in their structure and for their ability to transpose within the host genome, of which they make up a considerable portion. Copia- and Gypsy-like retrotransposons are the two main classes of retroelements shown to be ubiquitous in plant genomes. Ideally, the retrotransposons life cycle results in the synthesis of a messenger RNA and then self-encoded proteins to process retrotransposon mRNA in double stranded extra-chromosomal cDNA copies which may integrate in new chromosomal locations. Results The RT-PCR and IRAP protocol were applied to detect the presence of Copia and Gypsy retrotransposon transcripts and of new events of integration in unstressed plants of a sunflower (Helianthus annuus L.) selfed line. Results show that in sunflower retrotransposons transcription occurs in all analyzed organs (embryos, leaves, roots, and flowers). In one out of sixty-four individuals analyzed, retrotransposons transcription resulted in the integration of a new element into the genome. Conclusion These results indicate that the retrotransposon life cycle is firmly controlled at a post transcriptional level. A possible silencing mechanism is discussed.</p
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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