Functions of Opsins in Drosophila Taste

Abstract

Highlights d Opsins are needed for bitter taste in Drosophila d Opsins are directly activated by bitter tastants d Role for opsins in taste is independent of light and retinal d Opsins sense low levels of tastants via a signaling cascade that includes TRPA1

The diverging evolutionary history of opsin genes in Diptera

“…Furthermore, the function of the newly duplicated opsin genes in D . melanogaster may even not be restricted to the visual process: for instance, it has been recently proposed that Rh1 , Rh4 and Rh7 are involved in chemo sensation(Leung & Montell 2017; Leung et al 2020) suggesting a co-option of visual genes in different sensory pathways. In mosquitos, the information on opsin gene expression is instead scant.…”

“…For instance, the high heterogeneity in the selective pressure acting on Rh7 (Figure S5), coupled with its fast evolution (i.e. high dN, Figure S4), may be associated to the diverse strategies adopted by the circadian clock in species with different ecology and latitudinal distribution (Menegazzi et al 2017) and to the newly discovered taste abilities of this opsin in D. melanogaster (Leung et al 2020; Leung & Montell 2017; see also supplementary materials for an extended discussion on the expression in D. melanogaster ). We found that the agricultural pest Drosophila suzukii is characterized by an increased selective pressure affecting Rh6 and Rh7 (Figure 3).…”

“…We found that the agricultural pest Drosophila suzukii is characterized by an increased selective pressure affecting Rh6 and Rh7 (Figure 3). These changes are interesting from an applicative point of view, as they may be linked to the peculiar circadian activity (Hansen et al 2019), colour recognition pattern (Little et al 2019), and even gustatory preferences(Crava et al 2016; Leung et al 2020) deriving from the evolution of this species’ new ecological lifestyle. In Anopheles the function of opsins is less understood when compared to Drosophila (Montell & Zwiebel 2016).…”

“…Although extra-retinal opsins have been documented in vertebrates for quite some time, all non-visual functions previously identified depended on photoreception nevertheless (Leung & Montell 2017). In the last few years work on Drosophila melanogaster has documented that opsins contribute to thermosensation in larvae ( Rh1, Rh5, Rh6) , to proprioception during larva locomotion ( Rh1, Rh6) , to adult hearing (Rh5, Rh6 and possibly Rh3, Rh4) and to adult bitter taste discrimination ( Rh1, Rh4, Rh7 )(Sokabe et al 2016; Zanini et al 2018; Senthilan et al 2012; Leung et al 2020). All these functions are independent from photoreception, which begs the question on how these sensory modalities avoid interference from light.…”

Seeing Nemo: molecular evolution of ultraviolet visual opsins and spectral tuning of photoreceptors in anemonefishes (Amphiprioninae)

“…Increased SWS1 opsin expression has been found in the damselfish, P. nagasakiensis during winter months and may be a visual tuning response for taking advantage of the higher UV . Seasonal changes in opsin gene expression levels have been reported to alter colour perception in widespread taxa (see review by Shimmura et al 2018 Leung & Montell, 2017) and most recently in taste (Leung et al 2020).…”