Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are major phase II detoxification enzymes involved in glycosylation of lipophilic endobiotics and xenobiotics, including phytoalexins. Nicotine, one of the most abundant secondary plant metabolites in tobacco, is highly toxic to herbivorous insects. Plant-herbivore competition is the major impetus for the evolution of large superfamilies of UGTs and other detoxification enzymes. However, UGT functions in green peach aphid (Myzus persicae) adaptation are unknown. In this study, we show that UGT inhibitors (sulfinpyrazone and 5-nitrouracil) significantly increased nicotine toxicity in M. persicae nicotianae, suggesting that UGTs may be involved in nicotine tolerance. In total, 101 UGT transcripts identified in the M. persicae genome/transcriptome were renamed according to the UGT Nomenclature Committee guidelines and grouped into 11 families, UGT329, UGT330, UGT339, UGT341–UGT345, and UGT348–UGT350, with UGT344 containing the most (57). Ten UGTs (UGT330A3, UGT339A2, UGT341A6, UGT342B3, UGT343C3, UGT344D5, UGT344D8, UGT348A3, UGT349A3, and UGT350A3) were highly expressed in M. persicae nicotianae compared to M. persicae sensu stricto. Knockdown of four UGTs (UGT330A3, UGT344D5, UGT348A3, and UGT349A3) significantly increased M. persicae nicotianae sensitivity to nicotine, suggesting that UGT expression in this subspecies may be associated with nicotine tolerance and thus host adaptation. This study reveals possible UGTs relevant to nicotine adaptation in tobacco-consuming M. persicae nicotianae, and the findings will facilitate further validation of the roles of these UGTs in nicotine tolerance.

Nicotine is one of the most toxic secondary plant metabolites in nature and it is highly toxic to herbivorous insects. The overexpression of CYP6CY3 and its homologous isozyme CYP6CY4 in Myzus persicae nicotianae is correlated with nicotine tolerance. The expanded (AC)_n repeat in promoter is the cis element for CYP6CY3 transcription. These repeat sequences are conserved in the CYP6CY3 gene from Aphis gossypii and the homologous P450 genes in Acyrthosiphon pisum. The potential transcriptional factors that may regulate CYP6CY3 were isolated by DNA pulldown and sequenced in order to investigate the underlying transcriptional regulation mechanism of CYP6CY3. These identified transcriptional factors, AhR and ARNT, whose abundance was highly correlated with an abundance of the CYP6CY3 gene, were validated. RNAi and co-transfection results further confirm that AhR and ARNT play a major role in the transcriptional regulation of the CYP6CY3 gene. When the CYP6CY3 transcript is destabilized by AhR/ARNT RNAi, the transcription of the CYP6CY4 is dramatically up-regulated, indicating a compensatory mechanism between the CYP6CY3 and CYP6CY4 genes. Our present study sheds light on the CYP6CY3 and CYP6CY4 mediated nicotine adaption of M. persicae nicotianae to tobacco. The current studies shed light on the molecular mechanisms that underlie the genotypic and phenotypic changes that are involved in insect host shifts and we conclude that AhR/ARNT regulate the expression of CYP6CY3 and CYP6CY4 cooperatively, conferring the nicotine adaption of M. persicae nicotianae to tobacco

Background: Color vision and phototactic behavior based on opsins are important for the fitness of insects because of their roles in foraging and mate choice. Related topics, including the duplication and loss of opsin genes, have been well investigated in insect orders such as Coleoptera, Lepidoptera, Hymenoptera, Odonata and Orthoptera, and the findings have been used to develop pest management strategies involving light trapping. Mirid bugs of Hemiptera, which are pests that cause heavy economic losses, show capacity for color discrimination and phototaxis. However, the opsins in mirid bugs remain uncharacterized. Herein, we examined five species to investigate the evolution of opsins in the family Miridae.Results: Using RNA-seq, we identified several contigs showing high identity with opsins, including four contigs inApolygus lucorumand three contigs each inAdelphocoris suturalis,Adelphocoris fasciaticollis,Adelphocoris lineolatusandNesidiocoris tenuis. Phylogenetic analyses indicated that one of these genes clustered with ultraviolet-sensitive (UV) opsins and that the others clustered with long-wavelength (LW) opsins, suggesting that duplication of LW opsins and loss of blue light-sensitive (B) opsins occurred in mirid bugs. The existence of introns in the LW opsins of mirid bugs suggested that the duplication events were DNA based. Both LW1 and LW2 opsins of mirid bugs were found to be under strong purifying selection. The LW1 opsins were significantly more highly expressed than the LW2 and UV opsins.Conclusions: We identified the opsins of mirid bugs using five selected mirid species as a representative sample. Phylogenetic analyses clustered one of the genes with UV opsins and the others with LW opsins, suggesting the occurrence of LW opsin duplication and B opsin loss during the evolution of mirid bugs. Intron detection suggested that the identified duplication event was DNA based. The evidence of strong purifying selection and the relatively high expression levels suggested that these opsins exhibit fundamental functions in mirid bugs.

Because visual genes likely evolved in response to their ambient photic environment, the dichotomy between closely related nocturnal moths and diurnal butterflies forms an ideal basis for investigating their evolution. To investigate whether the visual genes of moths are associated with nocturnal dim-light environments or not, we cloned long-wavelength (R), blue (B) and ultraviolet (UV) opsin genes from 12 species of wild-captured moths and examined their evolutionary functions. Strong purifying selection appeared to constrain the functions of the genes. Dark-treatment altered the levels of mRNA expression in Helicoverpa armigera such that R and UV opsins were up-regulated after dark-treatment, the latter faster than the former. In contrast, B opsins were not significantly up-regulated. Diel changes of opsin mRNA levels in both wild-captured and lab-reared individuals showed no significant fluctuation within the same group. However, the former group had significantly elevated levels of expression compared with the latter. Consequently, environmental conditions appeared to affect the patterns of expression. These findings and the proportional expression of opsins suggested that moths potentially possessed color vision and the visual system played a more important role in the ecology of moths than previously appreciated. This aspect did not differ much from that of diurnal butterflies.