寄主植物与共生菌协同调控棉蚜寄主专化性的机理

The previous studies of applicant found that the infection rates of Arsenophonus nasoniae in the cotton-specialized aphids were significantly higher than that in the cucurbit-specialized aphids, but the population density of Buchnera aphidicola was significantly lower than the latter. Host plant not only manipulates the population size of Buchnera, but also determines the host range of host-specialized aphids. It has been known that the Buchnera can supply nutrients which are necessary for aphids but not ingest from host plant. Therefore, applicant presumes that the manipulation of host specialization of cotton-melon aphids Aphis gossypii would be controlled by the host plant and endosymbionts in aphids. In this project, the cotton- and cucurbit-specialized cotton aphids maintained in laboratory will be used. The species and infection rates of endosymbionts in aphids will be examined. The effects of host nutrients and plant secondary metabolites on community structure of symbionts infected with aphids, the population sizes of Buchnera, biosynthesis of amino acids, population differentiation of Buchnera, and relationship between Arsenophonus and Buchnera will be studied. Finally, the host use of cotton-melon aphids when their endosymbionts were changed will also be examined. These results will unfold the relationships between host plant, aphids and endosymbionts, and indicate the mechanism of host plant and endosymbionts together manipulating host-specialization of cotton-melon aphids. This study will develop a new ecological strategy for managing aphid populations based on the scientific allocation of crops to naturally suppress the roles of endosymbionts in aphids.

申请者研究发现，棉花型棉蚜感染次生菌Arsenophonus的比率高于瓜型棉蚜，而原生菌Buchnera的密度却显著低于后者，并且寄主植物能显著影响棉蚜体内Buchnera菌的种群大小、改变专化型棉蚜的寄主范围。前人研究已明确Buchnera菌能为蚜虫提供必需的营养。由此申请者推测，棉蚜寄主专化性很可能是寄主植物与棉蚜体内共生菌协同调控的结果。因此，本项目以棉花型和瓜型棉蚜为对象，拟进行两寄主型和不同寄主植物上棉蚜种群携带共生菌种类的确定，研究植物营养及次生物质对蚜虫体内共生菌群落组成、Buchnera种群大小和氨基酸合成、Buchnera种群遗传分化、次生菌与原生菌的种间关系等的影响，并检测共生菌种群变化后棉蚜的寄主利用能力等。研究结果将揭示植物-蚜虫-共生菌三者间的关系，明确寄主植物和共生菌协同调控棉蚜寄主专化性的机理，提出基于作物种类搭配的“作物抑菌控蚜”新策略。

棉蚜种群存在明显的寄主专化型，但是寄主专化型的调控机理仍不清楚。本项目在前期发现棉花型和瓜型棉蚜可通过特定中间寄主改变其寄主范围，并且两专化型棉蚜体内原生菌Buchnera密度和次生菌感染率存在显著差异的基础上，继续探讨寄主植物和共生菌协同调控棉蚜寄主专化性的机理。研究结果表明，不同寄主植物上的棉蚜种群感染次生共生菌群落的结构不同；棉花和豇豆上的棉蚜感染杀雄菌Arsenophonus比率高，而黄瓜上的很少感染。寄主植物的种类及环境温度影响杀雄菌的垂直传播；在西葫芦上，棉蚜杀雄菌垂直传代率低于在棉花上；30oC高温下杀雄菌很难传代。寄主植物通过次生物质和氨基酸营养来改变棉蚜体内原生菌和杀雄菌的种群密度。杀雄菌感染不仅可提高棉蚜种群在寄主植物上的适合度，而且可提高棉蚜在缺少氨基酸饲料上的繁殖力。杀雄菌感染提高了棉蚜对Phe氨基酸的需求，但降低了对Leu的需求。棉花叶片中的游离氨基酸含量显著低于黄瓜，而次生物质类黄酮和总酚的含量却显著高于黄瓜。感染杀雄菌的棉蚜体内3种氨基酸的含量显著高于不感染的棉蚜；但降低原生菌密度后，所有氨基酸的含量均是感染杀雄菌的显著低于不感菌的；杀雄菌不能独立合成氨基酸，但能与原生菌互作促进特定氨基酸的合成。棉花型和瓜型棉蚜体内原生菌和杀雄菌存在基因序列上的显著分化，棉花型和瓜型棉蚜不仅存在杀雄菌感染率的不同，而且存在杀雄菌基因型的差异。在缺精氨酸饲料上的棉蚜，其原生菌合成精氨酸相关酶基因表达水平上调，以促进氨基酸合成。研究建立了基于共生菌营养调控的棉蚜在棉花和黄瓜寄主间的间接转移通道。总之，寄主植物通过次生物质酚类调节棉蚜体内杀雄菌种群的密度，杀雄菌通过与原生菌的互作调控氨基酸的合成，从而为棉蚜提供特定的营养，满足棉蚜在特定寄主植物上生活，从而形成对特定寄主植物的专化型。由此，我们可以利用杀雄菌灭除技术，降低棉蚜种群感染杀雄菌的比率，从而降低棉蚜对寄主的适合度，达到控制棉蚜的效果。