Maha Mezghani Khemakhem

Bemisia tabaci (Aleyrodidae family) is one of the most damaging pests of numerous crops worldwide. Insecticides, namely pyrethroids and organophosphates, have long been the primary control tools against this pest, resulting in several resistance cases. In Tunisia, the two most damaging biotypes of B. tabaci, MEAM1-B and MED-Q, are sympatric, and more concerns about developing resistance keep rising due to the extensive use of insecticides. Here, we aimed to elucidate the molecular mechanism of resistance to pyrethroids and organophosphorus insecticides in two Tunisian populations of B. tabaci, collected respectively on Capsicum annuum and Lantana camara, and then determine the bacterial community associated with insecticide resistance and susceptible biotypes based on 16S rRNA Illumina sequencing. The results showed that the population collected on Capsicum annuum belonged to the MEAM1-B biotype with an insecticide resistance profile. In contrast, the population collected on the Lantana camara belonged to the MED-Q biotype with a sensitive profile. The bacterial communities of the two biotypes were predominantly structured by the Proteobacteria phylum and three genera, including Candidatus Portiera, the secondary facultative symbiont, and Hamiltonella, which were unevenly distributed between the two biotopes. Our results provide the first evidence for insecticide resistance alleles in Tunisian MEAM1-B populations and suggest an association between bacterial community composition within susceptible biotypes and insecticide resistance.

The date palm (Phoenix dactylifera L.) is a key crop in the arid regions of North Africa and the Middle East, with substantial socioeconomic value. Although multiple genome assemblies have been generated using next-generation sequencing (NGS) technologies, they primarily focus on Middle Eastern cultivars, leaving North African varieties unrepresented. This study aims to address this gap by sequencing and assembling the first genome of a North African date palm using Illumina sequencing technology. We present a draft genome assembly of the elite Tunisian variety Deglet Nour. By comparing it with the Barhee BC4 reference genome, we identify key genetic variants, including single nucleotide polymorphisms (SNPs) and insertions/deletions (INDELs), potentially associated with ripening processes and fruit quality. This work expands the genomic resources for date palm research, particularly for North African cultivars, and provides new insights into the nucleotide-level variability of the genes linked to key agronomic traits.

Tc1/mariner elements are ubiquitous in eukaryotic genomes including insects. They are diverse and divided into families and sub-families. The DD34D family including mauritiana and irritans subfamilies have already been identified in two closely related species of Cecidomyiids M. destructor and M. hordei. In the current study the de novo and similarity-based methods allowed the identification for the first time of seven consensuses in M. destructor and two consensuses in M. hordei belonging to DD41D family whereas the in vitro method allowed the amplification of two and three elements in these two species respectively. Most of identified elements accumulated different mutations and long deletions spanning the N-terminal region of the transposase. Phylogenetic analyses showed that the DD41D elements were clustered in two groups belonging to rosa and Long-TIR subfamilies. The age estimation of the last transposition events of the identified Tc1/mariner elements in M. destructor showed different evolutionary histories. Indeed, irritans elements have oscillated between periods of silencing and reappearance while rosa and mauritiana elements have shown regular activity with large recent bursts. The study of insertion sites showed that they are mostly intronic and that some recently transposed elements occurred in genes linked to putative DNA-binding domains and enzymes involved in metabolic chains. Thus, this study gave evidence of the existence of DD41D family in two Mayetiola species and an insight on their evolutionary history.

Transposable elements (TEs) are genetically mobile units that move from one site to another within a genome. These units can mediate regulatory changes that can result in massive changes in genes expression. In fact, a precise identification of TEs can allow the detection of the mechanisms involving these elements in gene regulation and genome evolution. In the present study, a genome-wide analysis of the Hemipteran pest Bemisia tabaci was conducted using bioinformatics tools to identify, annotate and estimate the age of TEs, in addition to their insertion sites, within or near of the defensome genes involved in insecticide resistance. Overall, 1,292,393 TE copies were identified in the B. tabaci genome grouped into 4872 lineages. A total of 699 lineages were found to belong to Class I of TEs, 1348 belong to Class II, and 2825 were uncategorized and form the largest part of TEs (28.81%). The TE age estimation revealed that the oldest TEs invasion happened 14 million years ago (MYA) and the most recent occurred 0.2 MYA with the insertion of Class II TE elements. The analysis of TE insertion sites in defensome genes revealed 94 insertions. Six of these TE insertions were found within or near previously identified differentially expressed insecticide resistance genes. These insertions may have a potential role in the observed insecticide resistance in these pests.

Miniature inverted-repeat transposable elements MITEs are ubiquitous, non-autonomous class II transposable elements. The moths, Helicoverpa armigera and Helicoverpa zea, are recognized as the two most serious pest species within the genus. Moreover, these pests have the ability to develop insecticide resistance. In the present study, we conducted a genome-wide analysis of MITEs present in H. armigera and H. zea genomes using the bioinformatics tool, MITE tracker. Overall, 3570 and 7405 MITE sequences were identified in H. armigera and H. zea genomes, respectively. Comparative analysis of identified MITE sequences in the two genomes led to the identification of 18 families, comprising 140 MITE members in H. armigera and 161 MITE members in H. zea. Based on target site duplication (TSD) sequences, the identified families were classified into three superfamilies (PIF/harbinger, Tc1/mariner and CACTA). Copy numbers varied from 6 to 469 for each MITE family. Finally, the analysis of MITE insertion sites in defensome genes showed intronic insertions of 11 MITEs in the cytochrome P450, ATP-binding cassette transporter (ABC) and esterase genes in H. armigera whereas for H. zea, only one MITE was retrieved in the ABC-C2 gene. These insertions could thus be involved in the insecticide resistance observed in these pests.

Mariner-like elements (MLEs) are class II transposons belonging to the Tc1-mariner family that have successfully invaded many insect genomes. In the current study, the availability of the Hessian fly, Mayetiola destructor, genome has enabled us to perform in silico analysis of MLEs using a previously described mariner element (Desmar1) belonging to the mauritiana subfamily. Eighteen mauritiana-like elements were detected and clustered into three main groups: Desmar1-like, MauCons1, and MauCons2. Subsequently, in vitro analysis was carried out to investigate mauritiana-like elements in M. destructor as well as in Mayetiola hordei using primers designed from TIRs of previously identified MLEs. PCR amplifications were successful, and a total of 12 and 17 mauritiana-like elements were detected in M. destructor and M. hordei, respectively. Sequence analyses of mauritiana-like elements obtained in silico and in vitro have shown that MauCons1 and MauCons2 elements share low similarity with Desmar1 ranging from 50% to 55%, suggesting that different groups under the mauritiana subfamily have invaded the genomes of M. destructor and M. hordei. These groups were likely inherited by vertical transmission, which subsequently underwent different evolutionary histories. This work describes new mauritiana-like elements in M. destructor that are distinct from the previously discovered Desmar1 and provides the first evidence of MLEs belonging to the mauritiana subfamily in M. hordei.