A Global Landscape of Miniature Inverted-Repeat Transposable Elements in the Carrot Genome

Polymorphic insertions of DcSto miniature inverted-repeat transposable elements reveal genetic diversity structure within the cultivated carrot

Miniature inverted-repeat transposable elements (MITEs) are a potent source of polymorphisms in plant genomes. A genotyping system, named DcS-ILP, based on polymorphic insertions of Stowaway MITEs (DcStos) localized in introns and identified in the reference genome DH1, has been developed for carrot. Here, we report an extension of the DcS-ILP genotyping system by incorporation of non-reference insertions identified in resequenced genomes representing the eastern gene pool. We genotyped 52 carrot accessions representing the eastern and western carrot gene pools with 92 markers developed previously (western DcS-ILP panel) together with 84 newly developed markers (eastern DcS-ILP panel). Overall, the DcS-ILP markers revealed a highly structured genetic diversity separating the eastern and the western carrot accessions at K = 2 and differentiating Indian breeding lines from the eastern accessions at K = 3. The eastern DcS-ILP panel proved to be more robust with respect to the eastern carrot gene pool, while it provided little information on the western accessions, as many of the DcSto insertions present in the eastern gene pool were absent in the western gene pool. As the western carrot accessions represent improved cultivars, DcSto insertional polymorphisms allowed detection of a selection-driven bottleneck at the improvement stage. Selection in the course of the improvement stage generally operated on standing variation, as the subset of DcSto insertions present in the western carrot likely originated from transposition events preceding the separation of both gene pools. However, occasional frequency shifts in the opposite direction were also revealed, possibly indicating selection for favorable variants associated with DcSto insertions.

Discovery and genome-wide characterization of a novel miniature inverted repeat transposable element reveal genome-specific distribution in Glycine

BACKGROUND

Miniature inverted repeat transposable elements (MITEs) are a dynamic component responsible for genome evolution. Tourist MITEs are derived from and mobilized by elements from the harbinger superfamily.

OBJECTIVE

In this study, a novel family of Tourist-like MITE was characterized in wild soybean species Glycine falcata. The new GftoMITE1 was initially discovered as an insertional polymorphism of the centromere-specific histone H3 (CenH3) gene in G. falcata.

METHODS

Using polymerase chain reaction, cloning and sequencing approaches, we showed a high number of copies of the GftoMITE1 family. Extensive bioinformatic analyses revealed the genome-level distribution and locus-specific mapping of GftoMITE1 members in Glycine species.

RESULTS

Our results provide the first extensive characterization of the GftoMITE1 family and contribute to the understanding of the evolution of MITEs in the Glycine genus. Genome-specific GftoMITE1 was prominent in perennial wild soybean species, but not in annual cultivated soybean (Glycine max) or its progenitor (Glycine soja).

CONCLUSIONS

We discuss that the GftoMITE1 family reveals a single rapid amplification in G. falcata and could have potential implications for gene regulation and soybean breeding as an efficient genetic marker for germplasm utilization in the future.

Population genomics identifies genetic signatures of carrot domestication and improvement and uncovers the origin of high-carotenoid orange carrots

Here an improved carrot reference genome and resequencing of 630 carrot accessions were used to investigate carrot domestication and improvement. The study demonstrated that carrot was domesticated during the Early Middle Ages in the region spanning western Asia to central Asia, and orange carrot was selected during the Renaissance period, probably in western Europe. A progressive reduction of genetic diversity accompanied this process. Genes controlling circadian clock/flowering and carotenoid accumulation were under selection during domestication and improvement. Three recessive genes, at the REC, Or and Y2 quantitative trait loci, were essential to select for the high α- and β-carotene orange phenotype. All three genes control high α- and β-carotene accumulation through molecular mechanisms that regulate the interactions between the carotenoid biosynthetic pathway, the photosynthetic system and chloroplast biogenesis. Overall, this study elucidated carrot domestication and breeding history and carotenoid genetics at a molecular level.

Genome-wide characterization of Mariner-like transposons and their derived MITEs in the Whitefly Bemisia tabaci (Hemiptera: Aleyrodidae)

The whitefly, Bemisia tabaci is a hemipteran pest of vegetable crops vectoring a broad category of viruses. Currently, this insect pest showed a high adaptability and resistance to almost all the chemical compounds commonly used for its control. In many cases, transposable elements (TEs) contributed to the evolution of host genomic plasticity. This study focuses on the annotation of Mariner-like elements (MLEs) and their derived Miniature Inverted repeat Transposable Elements (MITEs) in the genome of B. tabaci. Two full-length MLEs belonging to mauritiana and irritans subfamilies were detected and named Btmar1.1 and Btmar2.1, respectively. Additionally, 548 defective MLE sequences clustering mainly into 19 different Mariner lineages of mauritiana and irritans subfamilies were identified. Each subfamily showed a significant variation in MLE copy number and size. Furthermore, 71 MITEs were identified as MLEs derivatives that could be mobilized via the potentially active transposases encoded by Btmar 1.1 and Btmar2.1. The vast majority of sequences detected in the whitefly genome present unusual terminal inverted repeats (TIRs) of up to 400 bp in length. However, some exceptions are sequences without TIRs. This feature of the MLEs and their derived MITEs in B. tabaci genome that distinguishes them from all the other MLEs so far described in insects, which have TIRs size ranging from 20 to 40 bp. Overall, our study provides an overview of MLEs, especially those with large TIRs, and their related MITEs, as well as diversity of their families, which will provide a better understanding of the evolution and adaptation of the whitefly genome.