世界性寄主选择性农业害虫——棉蚜的翅二型现象解析

姬继超，皇甫宁博，雒珺瑜，高雪珂，牛林，张帅，崔金杰

背景：世界性害虫棉蚜生活史中存在3种有翅型，即有翅孤雌蚜（winged parthenogenetic female，WPF）、性母（winged gynopara，GP）、雄蚜（winged male），这3种有翅型均由无翅孤雌蚜（wingless parthenogenetic female，WLPF）产生。关于棉蚜翅型分化的研究多集中于有翅孤雌蚜，有关性母与雄蚜翅分化的研究较少。此外，棉蚜3种有翅型的翅型分化中是否存在共同的分子机理也不明了。作者之前研究了棉蚜有翅孤雌蚜翅的分化，在本研究中，在室内诱导出了性母与雄蚜，并将二者的外形、内生殖系统、翅脉、生殖力等与WPF、WLPF做了比较。最后，通过RNA-seq测序技术鉴定了3种有翅蚜与WLPF相比共有的和各自特有的差异表达基因。

结果：新出生若蚜于短光照条件（光照8 h，黑暗16 h，18 ℃）下饲养至成虫时，将先后产生性母、雄蚜2种有翅型，且性母数量偏多：1头母蚜可产生14头性母、9头雄蚜。与无翅孤雌蚜相比，棉蚜3种有翅型的形态相似、翅脉相同，但前后翅长度不同，生殖系统与生殖力迥异。通过对4种翅型棉蚜进行RNA-seq建库测序共获得37090个注释基因，其中与无翅孤雌蚜相比，有翅孤雌蚜、性母分别有10867、19334个差异表达基因，3种有翅蚜有2335个共同差异表达基因（1658个上调，677个下调）。1658个共有上调基因显著富集于胰岛素、FoxO、MAPK、淀粉与蔗糖代谢、脂肪酸生物合成与降解等多个信号通路，暗示这些信号途径可能参与调控棉蚜翅型可塑性。选取其中44个差异倍数不同的基因，采取RT-qPCR方法对RNA-seq数据进行验证，结果显示，与无翅孤雌蚜相比，这些基因在3种有翅蚜中的表达水平与RNA-seq测序结果一致，表明测序结果可信。最后，讨论了胰岛素信号通路相关差异表达基因在棉蚜翅型分化中的潜在作用。

结论：本研究通过转移新生若蚜至短光照条件（光照8 h，黑暗16 h，18 ℃）饲养建立了室内诱导棉蚜性母、雄蚜的高效方法，并首次发现棉蚜有翅孤雌蚜、性母、雄蚜外部形态尤其是翅脉相似，而内生殖器官迥异。此外，本研究通过RNA-seq测序技术鉴定出了3种有翅型棉蚜相对于无翅孤雌蚜的共有差异表达基因（2335个）、特有差异表达基因（有翅孤雌蚜1470个，性母2419个，雄蚜10774个），并富集得到多个潜在参与调控棉蚜3种有翅蚜翅型分化的信号通路，如胰岛素信号通路、淀粉与蔗糖代谢通路。

TiTle:Insights into wing dimorphism in worldwide agricultural pest and host-alternating aphid Aphis gossypii

Authors: JI Jichao, HUANGFU Ningbo, LUO Junyu, GAO Xueke, NIU Lin, ZHANG Shuai & CUI Jinjie

[Background] The worldwide pest Aphis gossypii has three-winged morphs in its life cycle, namely, winged parthenogenetic female (WPF), winged gynopara (GP), and winged male, which are all produced by a wingless parthenogenetic female (WLPF). Most studies on A. gossypii have focused on WPF, while few have investigated GP and male. The shared molecular mechanism underlying the wing differentiation in the three wing morphs of A. gossypii remains unknown. The wing differentiation of WPF was explored in a previous study. Herein, GP and male were induced indoors. The characters of the body, internal genitals, wing veins, and fecundity of GP and male were compared with those of WPF or WLPF. Compared with WLPF, the shared and separate differentially expressed genes (DEGs) were identified in these three-wing morphs.

[Results] Newly-born nymphs reared in short photoperiod condition (8?L:16D, 18?°C) exclusively produced gynoparae (GPe) and males in adulthood successively, in which the sex ratio was GP biased. A total of 14 GPe and 9 males were produced by one mother aphid. Compared with WLPF, the three-wing morphs exhibited similar morphology and wing vein patterns but were obviously discriminated in the length of fore- and underwings, reproductive system, and fecundity. A total of 37 090 annotated unigenes were obtained from libraries constructed using the four morphs via RNA sequencing (RNA-Seq). In addition, 10 867 and 19 334 DEGs were identified in the pairwise comparison of GP versus WLPF and male versus WLPF, respectively. Compared with WLPF, the winged morphs demonstrated 2 335 shared DEGs (1 658 upregulated and 677 downregulated). The 1 658 shared upregulated DEGs were enriched in multiple signaling pathways, including insulin, FoxO, MAPK, starch and sucrose metabolism, fatty acid biosynthesis, and degradation, suggesting their key roles in the regulation of wing plasticity in the cotton aphid. Forty-four genes that spanned the range of differential expression were chosen to validate statistical analysis based on RNA-Seq through the reverse transcription quantitative real time polymerase chain reaction (RT-qPCR). The comparison concurred with the expression pattern (either up- or downregulated) and supported the accuracy and reliability of RNA-Seq. Finally, the potential roles of DEGs related to the insulin signaling pathway in wing dimorphism were discussed in the cotton aphid.

[Conclusions] The present study established an efficiently standardized protocol for GP and male induction in cotton aphid by transferring newly-born nymphs to short photoperiod conditions (8?L:16D, 18?°C). The external morphological characters, especially wing vein patterns, were similar among WPFs, GPe, and males. However, their reproductive organs were strikingly different. Compared with WLPF, shared (2 335) and exclusively (1 470 in WLPF, 2 419 in GP, 10 774 male) expressed genes were identified in the three-wing morphs through RNA-Seq, and several signaling pathways that are potentially involved in their wing differentiation were obtained, including insulin signaling, starch and sucrose metabolism.

Journal of Cotton Research. 2021, 4: 5

https://doi.org/10.1186/s42397-021-00080-w

https://jcottonres.biomedcentral.com/articles/10.1186/s42397-021-00080-w