phased-fig-ficus-carica-l-genome.
Blackberries (Rubus spp.) are the fourth most economically important berry crop worldwide. Genome assemblies and annotations have been developed for Rubus species in subgenus Idaeobatus, including black raspberry (R. occidentalis), red raspberry (R. idaeus), and R. chingii, but very few genomic resources exist for blackberries and their relatives in subgenus Rubus. Here we present a chromosome-length assembly and annotation of the diploid blackberry germplasm accession ‘Hillquist’ (R. argutus). ‘Hillquist’ is the only known source of primocane-fruiting (annual-fruiting) in tetraploid fresh-market blackberry breeding programs and is represented in the pedigree of many important cultivars worldwide. The ‘Hillquist’ assembly, generated using PacBio long reads scaffolded with Hi-C sequencing, consisted of 298 Mb, of which 270 Mb (90%) was placed on seven chromosome-length scaffolds with an average length of 38.6 Mb. Approximately 52.8% of the genome was composed of repetitive elements. The genome sequence was highly collinear with a novel maternal haplotype-resolved linkage map of the tetraploid blackberry selection A-2551TN and genome assemblies of R. chingii and red raspberry. A total of 38,503 protein-coding genes were predicted using the assembly and Iso-Seq and RNA-seq data, of which 72% were functionally annotated. Eighteen flowering gene homologs within a previously mapped locus aligning to an 11.2 Mb region on chromosome Ra02 were identified as potential candidate genes for primocane-fruiting. The utility of the ‘Hillquist’ genome has been demonstrated here by the development of the first genotyping-by-sequencing based linkage map of tetraploid blackberry and the identification of possible candidate genes for primocane-fruiting. This chromosome-length assembly will facilitate future studies in Rubus biology, genetics, and genomics and strengthen applied breeding programs.
Members of CYCLOIDEA (CYC)/TEOSINTE BRANCHED1 (TB1) transcription factor family are essential to control flower symmetry and inflorescence architecture. In the Helianthus annuus genome, ten CYC/TB1 genes have been identified. Studies performed on mutants recognised HaCYC2c as one of the key players controlling zygomorphism in sunflower. We identified CYC2c genes in the diploid Helianthus decapetalus (HdCYC2c) and in the interspecific hybrid Helianthus × multiflorus (H × mCYC2cA and H × mCYC2cB), a triploid (2n = 3× = 51), originated from unreduced eggs of H. decapetalus fertilised by reduced H. annuus male gametes. Phylogenetic analysis showed that HdCYC2c and H × mCYC2c were placed within a CYC2 subclade together with HaCYC2c but distinct from it. The present data showed that in H. × multiflorus the allele derived from H. annuus is deleted or highly modified. The H. × multiflorus taxon exists as radiate and ligulate inflorescence types. We analysed CYC2c expression in H. decapetalus and in the cultivar 'Soleil d'Or' of H. × multiflorus, a ligulate inflorescence type with actinomorphic corolla of disk flowers transformed into a zygomorphic ray-like corolla. In H. decapetalus, the HdCYC2c gene showed differential expression between developing flower types, being up-regulated in the corolla of ray flowers in comparison to the disk flower corolla. In H. × multiflorus, an insertion of 865 bp, which is part of a CACTA transposable element, was found in the 5'-untranslated region (5'-UTR) of H × mCYC2cB. This insertion could promote, even with epigenetic mechanisms, ectopic expression of the gene throughout the inflorescence, resulting in the observed loss of actinomorphy and originating a ligulate head.
Genome skimming was performed, using Illumina sequence reads, in order to obtain a detailed comparative picture of the repetitive component of the genome of Populus species. Read sets of seven Populus and two Salix species (as outgroups) were subjected to clustering using RepeatExplorer (Novak et al. 2010). The repetitive portion of the genome ranged from 33.8 in P. nigra to 46.5% in P. tremuloides. The large majority of repetitive sequences were long terminal repeat-retrotransposons. Gypsy elements were over-represented compared to Copia ones, with a mean ratio Gypsy to Copia of 6.7 : 1. Satellite DNAs showed a mean genome proportion of 2.2%. DNA transposons and ribosomal DNA showed genome proportions of 1.8 and 1.9%, respectively. The other repeats types accounted for less of 1% each. Long terminal repeat-retrotransposons were further characterized, identifying the lineage to which they belong and studying the proliferation times of each lineage in the different species. The most abundant lineage was Athila, which showed large differences among species. Concerning Copia lineages, similar transpositional profiles were observed among all the analyzed species; by contrast, differences in transpositional peaks of Gypsy lineages were found. The genome proportions of repeats were compared in the seven species and a phylogenetic tree was built, showing species separation according to the botanical section to which the species belongs, although significant differences could be found within sections, possibly related to the different geographical origin of the species. Overall, the data indicate that the repetitive component of the genome in the poplar genus is still rapidly evolving.
GeneticaA computational genome-wide analysis of long terminal repeats retrotransposon expression in sunflower roots (Helianthus annuus L.
Transposable elements (TEs) are DNA sequences that can change their position within genomes. TEs are present in most organisms and can be an important genomic component. Their activities are manifold: restructuring of genome size, chromosomal rearrangements, induction of gene mutations, and alteration of gene activity by insertion near or within promoters, intronic regions, or enhancer. There are several examples of mutations and other genetic variations determined by the activity of TEs, associated with the evolution of prokaryotic and eukaryotic organisms and the domestication of plants. Generally, TE mobilization occurs when the organism is subjected to stress, which can include both biotic and abiotic stresses, polyploidy conditions, and interspecific hybridizations, very common events in plants. TEs are widely distributed among organisms. TEs also play essential roles in evolution, but most of them are either dormant or inactive. This is mainly determined by epigenetic silencing mechanisms, regulatory systems, and control systems that aim to limit its proliferation. Furthermore, the host has recruited many genes originated from TEs as transcriptional regulators, especially in defense against pathogens and invasive genetic elements; this phenomenon is called molecular domestication. Therefore, TEs are responsible for horizontal gene transfer and the movement of genetic material between organisms, even phylogenetically distant, with a consequent remixing of their gene pools.
We identified and characterized the pseudogene complements of five plant species: four dicots (Arabidopsis thaliana, Vitis vinifera, Populus trichocarpa and Phaseolus vulgaris) and one monocot (Oryza sativa). Retroposition was considered of modest importance for pseudogene formation in all investigated species except V. vinifera, which showed an unusually high number of retro-pseudogenes in non coding genic regions. By using a pipeline for the classification of sequence duplicates in plant genomes, we compared the relative importance of whole genome, tandem, proximal, transposed and dispersed duplication modes in the pseudo and functional gene complements. Pseudogenes showed higher tendencies than functional genes to genomic dispersion. Dispersed pseudogenes were prevalently fragmented and showed high sequence divergence at flanking regions. On the contrary, those deriving from whole genome duplication were proportionally less than expected based on observations on functional loci and showed higher levels of flanking sequence conservation than dispersed pseudogenes. Pseudogenes deriving from tandem and proximal duplications were in excess compared to functional loci, probably reflecting the high evolutionary rate associated with these duplication modes in plant genomes. These data are compatible with high rates of sequence turnover at neutral sites and double strand break repairs mediated duplication mechanisms.
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