Comparison of the Malpighian tubules and fat body transcriptional profiles of Zophobas morio larvae (Coleoptera: Tenebrionidae)

Biosensing firefly luciferin synthesis in bacteria reveals a cysteine-dependent quinone detoxification route in Coleoptera

Luciferin biosynthetic origin and alternative biological functions during the evolution of beetles remain unknown. We have set up a bioluminescent sensing method for luciferin synthesis from cysteine and benzoquinone using E. coli and Pichia pastoris expressing the bright Amydetes vivianii firefly and P. termitilluminans click beetle luciferases. In the presence of d-cysteine and benzoquinone, intense bioluminescence is quickly produced, indicating the expected formation of d-luciferin. Starting with l-cysteine and benzoquinone, the bioluminescence is weaker and delayed, indicating that bacteria produce l-luciferin, and then racemize it to d-luciferin in the presence of endogenous esterases, CoA and luciferase. In bacteria the p-benzoquinone toxicity (I_C50 ~ 25 µM) is considerably reduced in the presence of cysteine, maintaining cell viability at 3.6 mM p-benzoquinone concomitantly with the formation of luciferin. Transcriptional analysis showed the presence of gene products involved with the sclerotization/tanning in the photogenic tissues, suggesting a possible link between these pathways and bioluminescence. The lack of two enzymes involved with the last steps of these pathways, indicate the possible accumulation of toxic quinone intermediates in the lanterns. These results and the abundance of cysteine producing enzymes suggest that luciferin first appeared as a detoxification byproduct of cysteine reaction with accumulated toxic quinone intermediates during the evolution of sclerotization/tanning in Coleoptera.

Comparative analyses of transcriptional responses of Dectes texanus LeConte (Coleoptera: Cerambycidae) larvae fed on three different host plants and artificial diet

Dectes texanus is an important coleopteran pest of soybeans and cultivated sunflowers in the Midwestern United States that causes yield losses by girdling stems of their host plants. Although sunflower and giant ragweed are primary hosts of D. texanus, they began colonizing soybeans approximately 50 years ago and no reliable management method has been established to prevent or reduce losses by this pest. To identify genes putatively involved when feeding soybean, we compared gene expression of D. texanus third-instar larvae fed soybean to those fed sunflower, giant ragweed, or artificial diet. Dectes texanus larvae differentially expressed 514 unigenes when fed on soybean compared to those fed the other diet treatments. Enrichment analyses of gene ontology terms from up-regulated unigenes in soybean-fed larvae compared to those fed both primary hosts highlighted unigenes involved in oxidoreductase and polygalacturonase activities. Cytochrome P450s, carboxylesterases, major facilitator superfamily transporters, lipocalins, apolipoproteins, glycoside hydrolases 1 and 28, and lytic monooxygenases were among the most commonly up-regulated unigenes in soybean-fed larvae compared to those fed their primary hosts. These results suggest that D. texanus larvae differentially expressed unigenes involved in biotransformation of allelochemicals, digestion of plant cell walls and transport of small solutes and lipids when feeding in soybean.

TmDorX2 positively regulates antimicrobial peptides in Tenebrio molitor gut, fat body, and hemocytes in response to bacterial and fungal infection

Dorsal, a member of the nuclear factor-kappa B (NF-κB) family of transcription factors, is a critical downstream component of the Toll pathway that regulates the expression of antimicrobial peptides (AMPs) against pathogen invasion. In this study, the full-length ORF of Dorsal was identified from the RNA-seq database of the mealworm beetle Tenebrio molitor (TmDorX2). The ORF of TmDorX2 was 1,482 bp in length, encoding a polypeptide of 493 amino acid residues. TmDorX2 contains a conserved Rel homology domain (RHD) and an immunoglobulin-like, plexins, and transcription factors (IPT) domain. TmDorX2 mRNA was detected in all developmental stages, with the highest levels observed in 3-day-old adults. TmDorX2 transcripts were highly expressed in the adult Malpighian tubules (MT) and the larval fat body and MT tissues. After challenging the larvae with Staphylococcus aureus and Escherichia coli, the TmDorX2 mRNA levels were upregulated 6 and 9 h post infection in the whole body, fat body, and hemocytes. Upon Candida albicans challenge, the TmDorX2 mRNA expression were found highest at 9 h post-infection in the fat body. In addition, TmDorX2-knockdown larvae exposed to E. coli, S. aureus, or C. albicans challenge showed a significantly increased mortality rate. Furthermore, the expression of 11 AMP genes was downregulated in the gut and fat body of dsTmDorX2-injected larvae upon E. coli challenge. After C. albicans and S. aureus challenge of dsTmDorX2-injected larvae, the expression of 11 and 10 AMPs was downregulated in the gut and fat body, respectively. Intriguingly, the expression of antifungal transcripts TmTenecin-3 and TmThaumatin-like protein-1 and -2 was greatly decreased in TmDorX2-silenced larvae in response to C. albicans challenge, suggesting that TmDorX2 regulates antifungal AMPs in the gut in response to C. albicans infection. The AMP expression profiles in the fat body, hemocytes, gut, and MTs suggest that TmDorX2 might have an important role in promoting the survival of T. molitor larvae against all mentioned pathogens.

Phylogenomic analyses and divergence time estimation of Elateroidea (Coleoptera) based on RNA-Seq data

Bioluminescence, the emission of visible light in a living organism, is an intriguing phenomenon observed in different species and environments. In terrestrial organisms, the bioluminescence is observed mainly in beetles of the Elateroidea superfamily (Coleoptera). Several phylogenetic studies have been used different strategies to propose a scenario for the origin and evolution of the bioluminescence within this group, however some of them showed incongruences, mainly about the relationship of the bioluminescent families. In order to increase the number of molecular markers available for Elateroidea species and to propose a more accurate phylogeny, with high supported topology, we employed the Next-Generation Sequencing (NGS) methodology to perform the RNA-Seq analysis of luminescent (Elateridae, Phengodidae, Rhagophthalmidae, and Lampyridae) and non-luminescent (Cantharidae) species of Neotropical beetles. We used the RNA-Seq data to construct a calibrated phylogeny of Elateroidea superfamily using a large number of nuclear molecular markers. The results indicate Lampyridae and Phengodidae/Rhagophthalmidae as sister-groups, suggesting that the bioluminescence evolved later in Elateridae than other families (Lampyridae, Phengodidae, and Rhagophthalmidae), and indicating the Upper Cretaceous as the period for the main diversification of Elateroidea bioluminescent species.