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.研究背景：节肢动物作为研究无脊椎动物视蛋白进化的经典模型，已受到广泛关注。然而，针对物种多样的甲虫（昆虫纲：鞘翅目）体内赋予视觉色素光谱敏感性的视蛋白多样性，相关研究仍相对匮乏。既往研究显示，甲虫似乎缺失通常对光谱“蓝光”区域具有敏感性的短波长敏感（short-wavelength-sensitive, SWS）视蛋白类群。但该结论与多项鞘翅目昆虫已确立的生理数据相悖。为探究可能弥补SWS视蛋白缺失的分子层面适应性机制，我们对一类已被证实具有短波敏感性的甲虫类群——吉丁甲科（Buprestidae）体内的视蛋白展开研究。本研究通过生成RNA-seq数据，从隶属于4个亚科的6种吉丁甲科昆虫（包含3对雌雄个体）的9个类群中鉴定视蛋白，并对所获视蛋白进行结构分析，将其与其他昆虫紫外（ultraviolet, UVS）、短波长、长波长（long-wavelength, LWS）这几类主要视蛋白类群的序列进行比对。 研究结果：所有9种吉丁甲科昆虫均在UVS和LWS两类视蛋白中各表达2个拷贝，这与此前所有针对成虫甲虫视蛋白表达的分子研究中仅获得单个拷贝的结果不符。未检测到任何SWS视蛋白类群。此外，雄性白蜡窄吉丁（Agrilus planipennis，翡翠灰螟（emerald ash borer, EAB））低水平表达第三种LWS视蛋白，推测其为幼虫型拷贝。后续同源性及结构分析显示，UVS和LWS拷贝中存在多个氨基酸替换，这些替换或可赋予短波光谱敏感性。 研究结论：本研究首次将已表达的视蛋白基因与已证实鞘翅目昆虫存在多峰光谱敏感性的电生理数据进行比对。我们首次报道了成虫甲虫体内存在视蛋白复制现象，该现象同时存在于UVS和LWS视蛋白类群中。通过与已知昆虫视蛋白的结构比对，我们提出：视蛋白复制及发色团结合口袋内的氨基酸变异，可解释本研究物种在可见光光谱短波区域的敏感性。本研究首次揭示了甲虫类群视觉系统的分子复杂性。