Properties of the various Botmar1 transcripts in imagoes of the bumble bee, Bombus terrestris (Hymenoptera: Apidae)

'Junk' that matters: the role of transposable elements in bumblebee genome evolution

Transposable elements (TEs) are mobile DNA sequences that are widely distributed in eukaryotic genomes, where they are known to serve as a major force in genome evolution. The phenotypic impacts of TEs, while less well-studied, have also been discovered. Bumblebees are globally important pollinators in natural ecosystems and agriculture. Although TEs comprise a small fraction of bumblebee genomes, emerging evidence suggests that TEs are the major contributor of genome size variation across species and are involved in the formation of new coding and regulatory sequences. We review recent discoveries related to TEs in bumblebees, as well as outlining three key questions for the future of the field. In the future, we argue long-read sequencing technologies and genome editing techniques will help us identify TEs in bumblebees, unveil mechanisms that could account for their silencing and limited abundance, and uncover their contributions to phenotypic diversification, ecological adaptation, and speciation.

A novel cluster of mariner-like elements belonging to mellifera subfamily from spiders and insects: implications of recent horizontal transfer on the South-West Islands of Japan

Mariner-like elements (MLEs) have been isolated from various eukaryotic genomes and they are divided into 15 subfamilies, including main five subfamilies: mauritiana, cecropia, mellifera/capitata, irritans, and elegans/briggsae. In the present study, MLEs belonging to mellifera subfamily were isolated from various spiders and insects (Hymenoptera and Lepidoptera) inhabiting the South-West Islands of Japan and neighboring regions. MLEs isolated from 15 different species formed a distinct novel cluster in mellifera subfamily. MLEs obtained from three different species [i.e., the bee Amegilla senahai subflavescens (Amsmar1), the wasp Campsomeris sp. (Casmar1), and the swallowtail butterfly Pachliopta aristolochiae (Paamar1)] contained an intact open reading frame that encoded a putative transposase. These transposases exhibited high similarity of 97.9% among themselves. In case of Casmar1, the presence of an intact ORF was found in high frequencies (i.e., 11 out of 12 clones). In addition, these transposases also showed the presence of a terminal inverted repeat-binding motif, DD(34)D and two highly conserved amino acid motifs, (W/L)(I/L)PHQL and YSP(D/N)L(A/S)P. These two motifs differed from previously known motifs, WVPHEL and YSPDLAP. MLEs isolated from these three different species may have been inserted into their genomes by horizontal transfer. Furthermore, the presence of an intact ORF suggests that they are still active in habitats along these isolated islands.

Genome sequence of a crustacean iridovirus, IIV31, isolated from the pill bug, Armadillidium vulgare

Members of the family Iridoviridae are animal viruses that infect only invertebrates and poikilothermic vertebrates. The invertebrate iridovirus 31 (IIV31) was originally isolated from adult pill bugs, Armadillidium vulgare (class Crustacea, order Isopoda, suborder Oniscidea), found in southern California on the campus of the University of California, Riverside, USA. IIV31 virions are icosahedral, have a diameter of about 135 nm, and contain a dsDNA genome 220.222 kbp in length, with 35.09 mol % G+C content and 203 ORFs. Here, we describe the complete genome sequence of this virus and its annotation. This is the eighth genome sequence of an IIV reported.

Profile of the mosaic element BTMR1 in the genome of the bumble bee Bombus terrestris (Hymenoptera: Apidae)

Co-evolution involving a mariner transposon, Botmar1 and the other repeats contained in the Bombus terrestris genome was investigated. We found that the 5'-region of Botmar1 forms one of the components of a mosaic element, known as B. terrestris mosaic repeat 1 (BTMR1), which is also composed of inner segments originating from two different retrotransposons and a pseudogene corresponding to an RNA methyltransferase cDNA. The fact that BTMR1 is interspersed within chromosomes and the differences in its abundance in different species indicate that it is very probably a mobile element. Nevertheless, the absences of direct or inverted repeats at its ends and of target site duplication indicate that its mobility is not ensured by a cardinal transposable element, but putatively by a Crypton-like element.