School of Ecology and Environment, Northwestern Polytechnical University, Xi'an, 710072, Shanxi, China.
State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, 650223, Yunnan, China.
BMC Genomics. 2021 Feb 17;22(1):120. doi: 10.1186/s12864-021-07400-z.
Insect body coloration often functions as camouflage to survive from predators or mate selection. Transportation of pigment precursors or related metabolites from cytoplasm to subcellular pigment granules is one of the key steps in insect pigmentation and usually executed via such transporter proteins as the ATP-binding cassette (ABC) transmembrane transporters and small G-proteins (e.g. Rab protein). However, little is known about the copy numbers of pigment transporter genes in the butterfly genomes and about the roles of pigment transporters in the development of swallowtail butterflies.
Here, we have identified 56 ABC transporters and 58 Rab members in the genome of swallowtail butterfly Papilio xuthus. This is the first case of genome-wide gene copy number identification of ABC transporters in swallowtail butterflies and Rab family in lepidopteran insects. Aiming to investigate the contribution of the five genes which are orthologous to well-studied pigment transporters (ABCG: white, scarlet, brown and ok; Rab: lightoid) of fruit fly or silkworm during the development of swallowtail butterflies, we performed CRISPR/Cas9 gene-editing of these genes using P. xuthus as a model and sequenced the transcriptomes of their morphological mutants. Our results indicate that the disruption of each gene produced mutated phenotypes in the colors of larvae (cuticle, testis) and/or adult eyes in G0 individuals but have no effect on wing color. The transcriptomic data demonstrated that mutations induced by CRISPR/Cas9 can lead to the accumulation of abnormal transcripts and the decrease or dosage compensation of normal transcripts at gene expression level. Comparative transcriptomes revealed 606 ~ 772 differentially expressed genes (DEGs) in the mutants of four ABCG transporters and 1443 DEGs in the mutants of lightoid. GO and KEGG enrichment analysis showed that DEGs in ABCG transporter mutants enriched to the oxidoreductase activity, heme binding, iron ion binding process possibly related to the color display, and DEGs in lightoid mutants are enriched in glycoprotein binding and protein kinases.
Our data indicated these transporter proteins play an important role in body color of P. xuthus. Our study provides new insights into the function of ABC transporters and small G-proteins in the morphological development of butterflies.
昆虫的体色通常起到伪装作用，以逃避捕食者或进行交配选择。色素前体或相关代谢物从细胞质运输到亚细胞色素颗粒是昆虫色素形成的关键步骤之一，通常通过 ATP 结合盒（ABC）跨膜转运蛋白和小 G 蛋白（如 Rab 蛋白）等转运蛋白来执行。然而，对于蝴蝶基因组中色素转运基因的拷贝数以及色素转运蛋白在燕尾蝶发育中的作用知之甚少。
本文在燕尾蝶 Papilio xuthus 的基因组中鉴定了 56 个 ABC 转运蛋白和 58 个 Rab 成员。这是首次在燕尾蝶中对 ABC 转运蛋白和鳞翅目昆虫 Rab 家族进行全基因组基因拷贝数鉴定。为了研究与果蝇或家蚕中研究充分的色素转运蛋白（ABCG：white、scarlet、brown 和 ok；Rab：lightoid）同源的五个基因在燕尾蝶发育过程中的贡献，我们使用 P. xuthus 作为模型，通过 CRISPR/Cas9 基因编辑这些基因，并对其形态突变体进行了转录组测序。结果表明，每个基因的敲除都会导致 G0 个体幼虫（表皮、睪丸）和/或成虫眼睛颜色的表型突变，但对翅膀颜色没有影响。转录组数据表明，CRISPR/Cas9 诱导的突变会导致基因表达水平上异常转录本的积累和正常转录本的减少或剂量补偿。比较转录组分析显示，四个 ABCG 转运蛋白突变体中有 606~772 个差异表达基因（DEGs），lightoid 突变体中有 1443 个 DEGs。GO 和 KEGG 富集分析表明，ABCG 转运蛋白突变体中的 DEGs 富集到氧化还原酶活性、血红素结合、铁离子结合过程，可能与颜色显示有关，而 lightoid 突变体中的 DEGs 富集到糖蛋白结合和蛋白激酶。
本研究表明这些转运蛋白在 P. xuthus 的体色中发挥重要作用。本研究为 ABC 转运蛋白和小 G 蛋白在蝴蝶形态发育中的功能提供了新的见解。
