Evidence of peripheral olfactory impairment in the domestic silkworms: insight from the comparative transcriptome and population genetics

Abstract

BackgroundThe insect olfactory system is a highly specific and sensitive chemical detector, which plays important roles in feeding, mating and finding an appropriate oviposition site. The ecological niche of Bombyx mori has changed greatly since domestication from B. mandarina, and its olfactory response to environmental odorants clearly decreased. However, the mechanisms that result in the olfactory impairment are largely unknown.ResultsThe antennal transcriptomes were compared between the domestic and wild silkworms. Comparison of the same sex between the domestic and wild silkworms revealed 1410 and 1173 differentially expressed genes (DEGs) in males and females, respectively. To understand the olfactory impairment, we mainly focused on the olfactory-related genes. In total, 30 olfactory genes and 19 odorant-degrading enzymes (ODEs) showed differential expression in the two comparisons, in which 19 and 14 were down-regulated in the domestic silkworm, respectively. Based on population genomic data, the down-regulated odorant receptors (ORs) showed a higher ratio of unique non-synonymous polymorphisms to synonymous polymorphisms (N/S ratio) in the domestic populations than that in the wild silkworms. Furthermore, one deleterious mutation was found in OR30 of the domestic population, which was located in transmembrane helix 6 (TM6).ConclusionsOur results suggested that down-regulation of the olfactory-related genes and relaxed selection might be the major reasons for olfactory impairment of the domestic silkworm reared completely indoor environment. Reversely, wild silkworm may increase expression and remove deleterious polymorphisms of olfactory-related genes to retain sensitive olfaction.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-5172-1) contains supplementary material, which is available to authorized users.

Modulation of Sex Pheromone Discrimination by a UDP-Glycosyltransferase in Drosophila melanogaster

“…In insects, the characterization of metabolizing enzymes received an increasing interest with regard to their role in insecticide resistance, adaptation to host plant volatile and their function; as ODEs, in the termination of the olfactory signal to maintain a relatively high olfactory sensitivity toward new stimuli. In particular, recent studies investigating the antennal transcriptome in different species identified varied ODEs including CYP, CES, GST and UGT [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. These reports have completed and confirmed the case-by-case identification of previously characterized ODEs [25][26][27][28][29][30][31].…”

“…In any case, our data reveal that this mechanism likely depends on the level of the UGT gene product: males combining both the mutation and the RNAi targeted in neural tissues showed a wild-type-like behavioral discrimination. This is reminiscent of a recent transcriptomic study performed in the Bombyx mori silkworm antenna which revealed that the olfactory impairment observed in the domestic strain is correlated with a decreased expression of ODEs (including some UGTs) as compared to the wild B. mori strain [15].…”

Chemosensory Characteristics of Two Semanotus bifasciatus Populations

“…At the same time, the olfactory response of S. bifasciatus populations from different places to the same attractant are varied (unpublished data). The genetic basis related to physiological differences of insects may be gene expression level differences or sequences variation [48][49][50]. We found that in males of S. bifasciatus, the expression levels of OBPs, ORs, and SNMPs of the Beijing population were obviously lower than those of the Shandong population, and most conserved SNPs of OBPs and ORs from the two populations were the ones that showed more diversity in the Beijing population.…”

“…Previous trapping variation in S. bifasciatus from two different sites indicated that the olfactory systems of these two populations were different (unpublished data). The reasons could be quantitative or qualitative diversities of their chemosensory genes [48][49][50]. Thus, to explore the quantitative differences in the olfactory systems of these two S. bifasciatus populations, we analyzed the expression levels of S. bifasciatus from the two sites.…”

Genetic and genomic analysis for cocoon yield traits in silkworm

“…In the silkworm, cocoon yield traits are also under control of domestication. Whole-genome resequencing of eight silkworm strains and seven wild silkworms from ecologically different regions has been conducted in our laboratory 36 . The selective sweep regions were identified in the whole genome, which showed extremely low heterozygosity and high F ST values relative to wild populations ( Fig.…”