Data from: A cure for the blues: opsin duplication and subfunctionalization for short-wavelength sensitivity in jewel beetles (Coleoptera: Buprestidae)

Background: Arthropods have received much attention as a model for studying opsin evolution in invertebrates. Yet, relatively few studies have investigated the diversity of opsin proteins that underlie spectral sensitivity of the visual pigments within the diverse beetles (Insecta: Coleoptera). Previous work has demonstrated that beetles appear to lack the short-wavelength-sensitive (SWS) opsin class that typically confers sensitivity to the “blue” region of the light spectrum. However, this is contrary to established physiological data in a number of Coleoptera. To explore potential adaptations at the molecular level that may compensate for the loss of the SWS opsin, we carried out an exploration of the opsin proteins within a group of beetles (Buprestidae) where short-wave sensitivity has been demonstrated. RNA-seq data were generated to identify opsin proteins from nine taxa comprising six buprestid species (including three male/female pairs) across four subfamilies. Structural analyses of recovered opsins were conducted and compared to opsin sequences in other insects across the main opsin classes—ultraviolet, short-wavelength, and long-wavelength. Results: All nine buprestids were found to express two opsin copies in each of the ultraviolet and long-wavelength classes, contrary to the single copies recovered in all other molecular studies of adult beetle opsin expression. No SWS opsin class was recovered. Furthermore, the male Agrilus planipennis (emerald ash borer—EAB) expressed a third LWS opsin at low levels that is presumed to be a larval copy. Subsequent homology and structural analyses identified multiple amino acid substitutions in the UVS and LWS copies that could confer short-wavelength sensitivity. Conclusions: This work is the first to compare expressed opsin genes against known electrophysiological data that demonstrate multiple peak sensitivities in Coleoptera. We report the first instance of opsin duplication in adult beetles, which occurs in both the UVS and LWS opsin classes. Through structural comparisons of known insect opsins, we suggest that opsin duplication and amino acid variation within the chromophore binding pocket explains sensitivity in the short-wavelength portion of the visible light spectrum in these species. These findings are the first to reveal molecular complexity of the color vision system within beetles.

背景：节肢动物作为研究无脊椎动物视蛋白演化的经典模型，已受到广泛关注。然而，针对物种多样的甲虫（昆虫纲：鞘翅目）中支撑视觉色素光谱敏感性的视蛋白蛋白多样性，相关研究仍较为匮乏。既往研究表明，甲虫似乎缺失短波长敏感型（short-wavelength-sensitive, SWS）视蛋白家族，该类视蛋白通常负责介导可见光“蓝光”区域的光谱敏感性。但这一结论与多项鞘翅目昆虫的既定生理实验数据相悖。为探究可能弥补SWS视蛋白缺失的分子层面适应性机制，我们针对已被证实具备短波长视觉敏感性的吉丁甲科（Buprestidae）类群开展视蛋白蛋白研究。我们通过转录组测序（RNA-seq）技术，从覆盖4个亚科的6种吉丁甲科昆虫（包含3组雌雄配对样本）的9个分类单元中鉴定视蛋白蛋白。对所获得的视蛋白进行结构分析，并将其与其他昆虫中紫外（ultraviolet, UVS）、短波长（short-wavelength-sensitive, SWS）和长波长（long-wavelength, LWS）三大主要视蛋白家族的序列进行比对。结果：本次研究的9个吉丁甲科样本均在紫外（UVS）和长波长（LWS）视蛋白家族中各表达2个拷贝，而此前所有关于成虫甲虫视蛋白表达的分子研究均仅检测到单拷贝。未检测到任何SWS视蛋白家族的序列。此外，雄性白蜡窄吉丁（Agrilus planipennis，俗称翡翠灰螟EAB）还低水平表达第3个LWS视蛋白拷贝，推测其为幼虫型视蛋白。后续同源性与结构分析显示，UVS和LWS拷贝中存在多处氨基酸替换，这些替换可能赋予其短波长光谱敏感性。结论：本研究首次将已表达的视蛋白基因与证实鞘翅目昆虫存在多峰光谱敏感性的已知电生理数据进行比对。本研究首次报道成虫甲虫中存在视蛋白基因重复现象，该重复同时发生于UVS和LWS视蛋白家族。通过与已知昆虫视蛋白的结构比对，我们提出：视蛋白基因重复以及生色团结合口袋内的氨基酸变异，可解释本研究物种对可见光短波长区域的敏感性。本研究结果首次揭示了甲虫类群色觉系统的分子复杂性。