Identification and expression analysis of chemosensory receptors in the tarsi of fall armyworm, Spodoptera frugiperda (J. E. Smith)

Abstract

Chemosensation of tarsi provides moths with the ability to detect chemical signals which are important for food recognition. However, molecular mechanisms underlying the chemosensory roles of tarsi are still unknown. The fall armyworm Spodoptera frugiperda is a serious moth pest that can damage many plants worldwide. In the current study, we conducted transcriptome sequencing with total RNA extracted from S. frugiperda tarsi. Through sequence assembly and gene annotation, 23 odorant receptors 10 gustatory receptors and 10 inotropic receptors (IRs) were identified. Further phylogenetic analysis with these genes and homologs from other insect species indicated specific genes, including ORco, carbon dioxide receptors, fructose receptor, IR co-receptors, and sugar receptors were expressed in the tarsi of S. frugiperda. Expression profiling with RT-qPCR in different tissues of adult S. frugiperda showed that most annotated SfruORs and SfruIRs were mainly expressed in the antennae, and most SfruGRs were mainly expressed in the proboscises. However, SfruOR30, SfruGR9, SfruIR60a, SfruIR64a, SfruIR75d, and SfruIR76b were also highly enriched in the tarsi of S. frugiperda. Especially SfruGR9, the putative fructose receptor, was predominantly expressed in the tarsi, and with its levels significantly higher in the female tarsi than in the male ones. Moreover, SfruIR60a was also found to be expressed with higher levels in the tarsi than in other tissues. This study not only improves our insight into the tarsal chemoreception systems of S. frugiperda but also provides useful information for further functional studies of chemosensory receptors in S. frugiperda tarsi.

Keywords: Spodoptera frugiperda; expression profile; gustatory receptor; ionotropic receptor; odorant receptor; tarsal transcriptome.

FIGURE 1

Phylogenetic analysis of the candidate SfruORs from the transcriptome of S. frugiperda tarsi and ORs from H. armigera and B. mori.

FIGURE 2

TPM values of candidate SfruORs in the tarsi of male and female S. frugiperda.

FIGURE 3

Expression patterns of candidate SfruORs in different chemosensory tissues of adult S. frugiperda. FA: female antennae, MA: male antennae, FP: female proboscises, MP: male proboscises, FT: female tarsi, MT: male tarsi, PG-OV: pheromone gland-ovipositor. Different letters indicate significant difference based on a one-way ANOVA followed by Tukey’s multiple comparison test. Error bars show the standard errors of the means (+SE), p < 0.05, n = 3.

FIGURE 4

Phylogenetic analysis of the candidate SfruGRs from the transcriptome of S. frugiperda tarsi and GRs from H. armigera and B. mori.

FIGURE 5

TPM values of candidate SfruGRs in the tarsi of male and female S. frugiperda.

FIGURE 6

Expression patterns of candidate SfruGRs in different chemosensory tissues of adult S. frugiperda. FA: female antennae, MA: male antennae, FP: female proboscises, MP: male proboscises, FT: female tarsi, MT: male tarsi, PG-OV: female pheromone gland-ovipositor. Different letters indicate significant difference based on a one-way ANOVA followed by Tukey’s multiple comparison test. Error bars show the standard errors of the means (+SE), p < 0.05, n = 3.

FIGURE 7

Phylogenetic analysis of the candidate SfruIRs from the transcriptome of S. frugiperda tarsi and IRs from H. armigera and D. melanogaster.

FIGURE 8

TPM values of candidate SfruIRs in the tarsi of male and female S. frugiperda.

FIGURE 9

Expression patterns of candidate SfruIRs in different chemosensory tissues of adult S. frugiperda. FA: female antennae, MA: male antennae, FP: female proboscises, MP: male proboscises, FT: female tarsi, MT: male tarsi, PG-OV: female pheromone gland-ovipositor. Different letters indicate significant difference based on a one-way ANOVA followed by Tukey’s multiple comparison test. Error bars show the standard errors of the means (+SE), p < 0.05, n = 3.