Tandem duplication of a genomic region encoding glutathione S-transferase epsilon-2 and -4 genes in DDT-resistant Anopheles stephensi strain from India

The origin, invasion history and resistance architecture of Anopheles stephensi in Africa

The invasion of Africa by the Asian urban malaria vector, Anopheles stephensi, endangers 126 million people across a rapidly urbanising continent where malaria is primarily a rural disease. Control of An. stephensi requires greater understanding of its origin, invasion dynamics, and mechanisms of widespread resistance to vector control insecticides. We present a genomic surveillance study of 551 An. stephensi sampled across the invasive and native ranges in Africa and Asia. Our findings support a hypothesis that an initial invasion from Asia to Djibouti seeded separate incursions to Sudan, Ethiopia, and Yemen before spreading inland, aided by favourable temperature, vegetation cover, and human transit conditions. Insecticide resistance in invasive An. stephensi is conferred by detoxification genes introduced from Asia. These findings, and a companion genomic data catalogue, will form the foundation of an evidence base for surveillance and management strategies for An. stephensi.

Differential detoxification enzyme profiles in C-corn strain and R-rice strain of Spodoptera frugiperda by comparative genomic analysis: insights into host adaptation

BACKGROUND

The fall armyworm (FAW) Spodoptera frugiperda, a highly invasive, polyphagous pest, poses a global agricultural threat. It has two strains, the C-corn and R-rice strains, each with distinct host preferences. This study compares detoxification enzyme gene families across these strains and related Spodoptera species to explore their adaptation to diverse host plant metabolites.

RESULTS

A total of 1,995 detoxification-related genes, including cytochrome P450 monooxygenases (CYPs), carboxylesterases (COEs), glutathione S-transferases (GSTs), UDP-glucuronosyltransferases (UGTs), and ATP-binding cassette transporters (ABCs), were identified across the genus Spodoptera, including S. littoralis, S. litura, S. picta, S. exigua, and both FAW strains. A higher abundance of phase I detoxification enzymes (CYPs and COEs) and GSTs was observed in Spodoptera species, while FAW strains exhibited fewer detoxification genes, with notable differences in copy numbers between the C and R strains. Analyses at the subfamily level revealed significant variation in gene distribution and expression, particularly within phase I and II detoxification enzymes. Expansions in CYP6AE were detected in the C strain, while contractions in GST-ε, CYP9A, CYP4M, UGT33B, and UGT33F occurred in both strains. In contrast, no substantial variation was observed in phase III ABC enzymes. Functional predictions and protein interaction networks suggest a broader expansion of metabolism-related genes in the R strain compared to the C strain.

CONCLUSIONS

These findings emphasize the pivotal role of phase I and II detoxification enzymes in host adaptation, providing molecular insights into FAW's capacity for host range expansion, which are crucial for devising targeted and sustainable pest management strategies.

The Fat Body-Specific GST Gene SlGSTe11 Enhances the Tolerance of Spodoptera litura to Cyantraniliprole and Nicotine

Spodoptera litura is a significant agricultural pest, and its glutathione S-transferase (GST) plays a crucial role in insecticide resistance. This study aimed to investigate the relationship between the SlGSTe11 gene of S. litura and resistance to cyantraniliprole and nicotine. Transcriptome analysis revealed that SlGSTe11 is highly expressed mainly in fat bodies, with a significant increase in SlGSTe11 gene expression under induction by cyantraniliprole and nicotine. The ectopic expression of the SlGSTe11 gene in transgenic fruit flies resulted in a 5.22-fold increase in the tolerance to cyantraniliprole. Moreover, compared to the UAS-SlGSTe11 line, the Act5C-UAS>SlGSTe11 line laid more eggs and had a lower mortality after nicotine exposure. RNAi-mediated inhibition of SlGSTe11 gene expression led to a significant increase in the mortality of S. litura under cyantraniliprole exposure. In vitro metabolism experiments demonstrated that the recombinant SlGSTe11 protein efficiently metabolizes cyantraniliprole. Molecular docking results indicated that SlGSTe11 has a strong affinity for both cyantraniliprole and nicotine. These findings suggest that SlGSTe11 is involved in the development of resistance to cyantraniliprole and nicotine in S. litura.

Heterologous expression and characterization of two delta glutathione S-transferases genes involved in imidacloprid metabolism in Grapholita molesta

Glutathione S-transferases (GSTs) are multifunctional enzymes, and insect GSTs play a pivotal role in the metabolism of insecticides. Grapholita molesta is a worldwide pest that causes substantial economic losses to the fruit industry. However, it remains unclear how imidacloprid, a commonly used insecticide in orchards, is metabolized by G. molesta. In the present study, the synergist diethyl maleate (DEM), which inhibits the GST activity, exhibited a 22-fold synergistic ratio against imidacloprid. Two new GST genes, GmGSTD2 (OR096251) and GmGSTD3 (OR096252), were identified and successfully cloned, showing the highest expression in the Malpighian tubes. Knockdown of GmGSTD2 and GmGSTD3 by RNA interference, increased the mortality of G. molesta from 28% to 47% following imidacloprid treatment. Both recombinant GmGSTD2 and GmGSTD3 proteins exhibited 1-chloro-2,4-dinitrobenzene (CDNB) activity and could be inhibited by imidacloprid in vitro, with maximum inhibition was 60% for GmGSTD2 and 80% for GmGSTD3. These results suggested that GSTs participate in the metabolism of imidacloprid with GmGSTD2 and GmGSTD3 playing key roles in this process.

Identification of putative promoter elements for epsilon glutathione s-transferases genes associated with resistance to DDT in the malaria vector mosquito anopheles arabiensis

The purpose of this study was to identify the putative regulatory elements in the promoter region of An. arabiensis strains which differed in susceptibility to DDT and compare with those identified in its sibling An. gambaie. Basal expression level of Epsilon class GSTs (Glutathione S - transferases) GSTe1 gene was 0.512 - 0.658 (95% CI) and GSTe2 0.672 - 1.204 (95% CI) in adults of DDT resistant KGB compared to 0.031 - 0.04 (95% CI) and 0.148 - 0.199 (95% CI) respectively in susceptible MAT strains of An. arabiensis. Induced mean expression of GSTe2 in larvae exposed to DDT for one hour was 0.901 - 1.172 (95% CI) in KGB and 0.475 - 0.724 (95% CI) in MAT strain. In present work, strain specific primers were used to amplify and sequenced the promoter regions of GSTe1 and GSTe2 in the KGB, MAT and field specimens. Computational analysis revealed presence of classical arthropod initiator sequence TCAGT and putative core promoter elements, GC, CAAT, TATA boxes. A typical TATA box was identified at 35 bp upstream Transcription Start Site (TSS) in GSTe1 but was absent in GSTe2. Several binding sites for regulatory elements downstream and multiple polymorphic sites were identified between strains. The role of these regulatory elements in transcription of these genes has not been determined. However, on comparison the 2 bp adenosine indel (insertion/deletion) which was essential in driving the promoter activity in An. gambiae was identified only DDT resistant KGB strain.

Two different types of tandem sequences mediate the overexpression of TinCYP51B in azole-resistant Trichophyton indotineae

Trichophyton indotineae is an emerging dermatophyte that causes severe tinea corporis and tinea cruris. Numerous cases of terbinafine- and azole-recalcitrant T. indotineae-related dermatophytosis have been observed in India over the past decade, and cases are now being recorded worldwide. Whole genome sequencing of three azole-resistant strains revealed a variable number of repeats of a 2,404 base pair (bp) sequence encoding TinCYP51B in tandem specifically at the CYP51B locus position. However, many other resistant strains (itraconazole MIC ≥0.25 µg/mL; voriconazole MIC ≥0.25 µg/mL) did not contain such duplications. Whole-genome sequencing of three of these strains revealed a variable number of 7,374 bp tandem repeat blocks harboring TinCYP51B. Consequently, two types of T. indotineae azole-resistant strains were found to host TinCYP51B in tandem sequences (type I with 2,404 bp TinCYP51B blocks and type II with 7,374 bp TinCYP51B blocks). Using the CRISPR/Cas9 genome-editing tool, the copy number of TinCYP51B within the genome of types I and II strains was brought back to a single copy. The azole susceptibility of these modified strains was similar to that of strains without TinCYP51B duplication, showing that azole resistance in T. indotineae strains is mediated by one of two types of TinCYP51B amplification. Type II strains were prevalent among 32 resistant strains analyzed using a rapid and reliable PCR test.