Genomics Analysis of L-DOPA Exposure inDrosophila sechellia

Abstract

Drosophila sechellia is a dietary specialist fruit fly that evolved from a generalist ancestor to specialize on the toxic fruit of Morinda citrifolia. This species pair has been the subject of numerous studies where the goal has largely been to determine the genetic basis of adaptations associated with host specialization. Because one of the most striking features of M. citrifolia fruit is the production of toxic volatile compounds that kill insects, most genomic studies in D. sechellia to date have focused on gene expression responses to the toxic compounds in its food. In this study, we aim to identify new genes important for host specialization by profiling gene expression response to 3,4-dihydroxyphenylalanine (L-DOPA). Recent work found it to be highly abundant in M. citrifolia, critical for reproductive success of D. sechellia, and supplementation of diet with the downstream pathway product dopamine can influence toxin resistance phenotypes in related species. Here we used a combination of functional genetics and genomics techniques to identify new genes that are important for D. sechellia ecological adaptation to this new niche. We show that L-DOPA exposure can affect toxin resistance phenotypes, identify genes with plastic responses to L-DOPA exposure, and functionally test an identified candidate gene. We found that knock-down of Esterase 6 (Est6) in a heterologous species alters toxin resistance suggesting Est6 may play an important role in D. sechellia host specialization.

Genomics analysis ofDrosophila sechelliaresponse toMorinda citrifoliafruit diet

“…Previous studies examining gene expression responses in D. sechellia to the volatile fatty acids in noni fruit have focused on examining all of the differentially expressed genes in response to either OA or HA treatment to identify genes involved in evolved toxin resistance (Lanno et al 2017, Lanno et al 2019a, Drum et al In Review (BIORXIV/2021). Interestingly, only 19.7% and 28.9% of DEGs found in these studies are responding to specifically to OA or HA treatment respectively, and only two genes are found that respond to both OA and HA treatment but no other treatments.…”

“…Expression of Osi6 and several other Osiris genes are significantly increased in D. sechellia in response to OA (Lanno et al 2017), and Osi6 is one of the 25 DEGs found only in OA and not in response to any of the other noni components. However, esterase 6 (Est-6) RNAi has been previously shown to alter survival in D. melanogaster exposed to OA and the activity of esterase enzymes has previously been shown to be involved in OA resistance (Lanno et al 2017, Lanno et al 2019a, Lanno et al 2019b. Interestingly, Est-6 expression is significantly enriched in response to L-DOPA and noni treatments, but not upon OA or HA exposure.…”

“…After sequencing output files were obtained from the University of Michigan Sequencing Core (Table 1), .fastq files containing raw sequencing reads were uploaded to the Galaxy platform (Afgan et al 2016) and an RNA-seq pipeline analysis was performed (Figure 1) as previously described (Lanno et al 2017and Lanno et al 2019a, Drum et al, In Review (BIORXIV/2021). Briefly, reads were assessed for quality using FASTQC (Andrews 2010) and any overrepresented sequences were analyzed using NCBI Blast (Altschul et al 1990).…”

“…Significantly differentially expressed genes identified in previous studies that examined OA, L-DOPA, and HA exposure in adult female D. sechellia flies (Lanno et al 2017;Lanno et al 2019a;Drum et al In Review (BIORXIV/2021/447576)) were used for i-cisTarget analysis in addition to DEGs we identified here in response to noni to predict transcription factors that control the plasticity of DEGs. For this analysis, all DEGs, both up-and down-regulated are used for all four treatments (OA, L-DOPA, HA and noni).…”

“…In addition, this process allows the eggs to survive in the fruit's toxic environment (Lavista-Llanos et al 2014). Furthermore, D. melanogaster and D. simulans adult flies fed L-DOPA have increased resistance to OA (Lavista-Llanos et al 2014, Lanno et al 2019a.…”