Characterisation of the Ultraviolet‐Sensitive Opsin Gene in the Honey Bee, Apis Mellifera

Abstract

The cDNA sequence of the ultraviolet-sensitive opsin in the honey-bee, Apis mellifera, with associated 5' and 3' untranslated regions, is presented. The analysis of genomic structure reveals seven introns in the coding region of the gene, with six at novel positions for an insect opsin gene. The equivalent site to the counterion in vertebrate opsins is occupied by a Tyr residue. This contrasts with the presence of Phe at this site in the ultraviolet-sensitive opsins of Drosophila sps. A comparison of the amino acid sequence within the seven a-helical transmembrane regions of insect ultraiiiolet/blue-sensitive opsins identifies substitution at five sites that involve either replacement of a polar with a non-polar residue, or a change in charge. Such changes are known to result in spectral shifts in \,errhate pigments. Phylogenetic analysis indicates that the ultraviolet-sensitive pigments represent an ancient class of insect opsins.Keywords: ultraviolet-sensitive opsin ; visual pigment ; spectral tuning ; honey bee ; Apis mellifera.The trichromatic basis of the colour vision in the honey bee, Apis mellqera, was first demonstrated by Daumer [I] using mixed colour trials with free-flying bees, and the ability to discriminate colours was confirmed electrophysiologically by Autrum and Zwehl [2]. Trichromacy in A. rnellqera is dependent on the presence of three classes of photoreceptors in the compound eye with peak sensitivities (Aman) at 540 nm (green-sensitive), 435 nm (blue-sensitive), and 335 nm (ultraviolet-sensitive) [3, 41. The i , , , , of each class of photoreceptor is determined by the presence of its own unique visual pigment. These visual pigments are composed of a protein moiety (opsin) that forms seven transmembrane a-helices. The chromophore, which in the case of the honey bee is 11-cis-retinal, is covalently bound via a protonated Schiff's base to a Lys residue in the seventh transmembrane region. Of the three rhodopsins present in the compound eye of A. mellifera, the ultraviolet-sensitive rhodopsin is perhaps the most interesting from ecological, physiological and phylogenetic perspectives.Ultraviolet-sensitive opsins in insects are believed to be important both for orientation by polarized ultraviolet light [5] and in the detection of nectar or honey guides which are present on the flowers of many species of plants [6]. However, to date, the only insect ultraviolet-sensitive opsins to have been studied at the molecular level are the Rh3 and Rh4 genes of Drosophila species [7-lo]; little is known about the mechanism of spectral tuning that shifts the peak sensitivity of these pigments to below that of native 11-cis-retinal at 380 nm.From an evolutionary perspective, it is unknown whether the ultraviolet-sensitive opsins of insects are a recent addition to

THEEVOLUTION OFCOLORVISION ININSECTS

“…Certainly, both of these can add noise to the measurements, but, unfortunately, the possibility that interindividual variance may also contribute has not been considered. Notably, honey bee opsins have been cloned in recent years (10,29,152), and allelic variation has been reported (152). However, no functional studies exist demonstrating that these alleles have any effect on honey bee spectral sensitivities.…”

Short wavelength-sensitive opsins from the Saharan silver and carpenter Ants

“…The other class of short wavelength-sensitive opsins is characterized by opsins that are maximally sensitive to blue wavelengths. As noted by Chase et al, (1997), the short wavelength opsin previously isolated from honeybees (Bellingham et al, 1997) is most likely a blue sensitive visual pigment, despite assertions to the contrary. Indeed, the opsin cloned by Beltingham et al, (1997) has been conclusively demonstrated to code for a visual pigment with maximum sensitivity at 439 nm (Townson et al, 1998).…”

In silico characterisation and chromosomal localisation of human RRH (peropsin) – implications for opsin evolution

“…An exception being encephalopsin which shares ~30% identity with other members of the classical opsin superfamily [12], but clearly has a highly conserved gene structure. The phenomenon of intron sliding or slippage [32], which has been proposed as a mechanism contributing to the slight variations in position of some introns observed between some insect opsins [33], may explain the 1 bp shift between intron 6 of RRH and intron 4 of the classical opsin superfamily, but their proximity may also be due to chance. Whilst single nucleotide intron slippage is an evolutionary phenomenon thought to occur in <5% of introns [34], these two opsin groups do not appear to have a recent common ancestor which probably indicates a random insertion of introns.…”