寄主植物對於銀葉粉蝨內共生菌的影響

Abstract

菸草粉蝨種群 (Bemisia tabaci) 為世界上重要的農業害蟲之一，除了透過刺吸取食植物汁液造成植物發育不良，也會傳播超過 200 種植物病毒，造成嚴重的農業損失。菸草粉蝨種群體內有多種內共生菌，包含一種主要內共生菌 (primary endosymbiont) 及七種次要內共生菌 (secondary endosymbionts)。主要共生菌 Portiera aleyrodidarum 可以提供粉蝨必需的營養，而次要共生菌（Hamiltonella defensa、Rickettsia sp. 等）對菸草粉蝨種群影響仍未被透徹了解。菸草粉蝨種群、內共生菌以及寄主植物之間有緊密的交互作用。相關文獻指出，菸草粉蝨種群取食不同寄主植物時，其體內內共生菌的數量有顯著的差異；然而，進一步探討此現象的研究仍不多。此研究將體內含有 P. aleyrodidarum、H. defensa 及 Rickettsia sp. 的銀葉粉蝨 (Bemisia argentifolii, 屬菸草粉蝨種群) 分別在五種不同的寄主植物（芥藍、棉花、胡瓜、聖誕紅及番茄）上連續飼養 20 個世代，每個世代皆從各寄主植物上取樣粉蝨，利用定量 PCR 測量在不同世代中粉蝨體內三種共生菌的數量變化，並檢測在各寄主植物上第一及第十世代粉蝨的生命相關表現 (performance) 與其體內 P. aleyrodidarum 的必需胺基酸生合成基因表現。研究結果顯示，銀葉粉蝨轉移至新寄主植物後的初幾個世代，P. aleyrodidarum 及 H. defensa 的數量會顯著下降，並於第五至第十世代時回升至原先的數量。此外，相較於第一世代，飼養於棉花的銀葉粉蝨在第十世代有更好的生命相關表現。過去研究顯示 P. aleyrodidarum 在營養方面與銀葉粉蝨有互利共生的關係，本研究近一步發現在粉蝨適應棉花的過程中，P. aleyrodidarum 的必需胺基酸生合成基因表現會受到調控。總而言之，主要共生菌會幫助銀葉粉蝨提升生命相關表現以及適應營養較差或是防禦較強的寄主植物。此研究成果奠定了銀葉粉蝨、內共生菌及寄主植物之間交互作用的研究基礎，並可以用於開發新穎的銀葉粉蝨防治策略。

Bemisia tabaci species complex is considered as a serious insect pest worldwide. It not only infests a broad range of host plants but also transmits more than 200 plant viruses. Bemisia tabaci species complex harbors several endosymbiotic bacteria called endosymbionts. Portiera aleyrodidarum is the primary endosymbiont that mainly provides B. tabaci species complex with essential nutrients, whereas the functions of secondary endosymbionts (e.g. Hamiltonella defensa, Rickettsia sp., etc.) are still little understood. Bemisia tabaci species complex, endosymbionts, and host plants have intimate interactions. It has been reported that the amounts of endosymbionts in B. tabaci species complex vary when it feeds on different host plants; however, few studies further examine this phenomenon. In this study, B. argentifolii (B. tabaci MEAM 1 putative species) harboring P. aleyrodidarum, H. defensa, and Rickettsia sp. was reared on five host plants (Chinese kale, cotton, cucumber, poinsettia, and tomato) respectively for 20 generations. The whiteflies were collected from each host plant in every generation, and then the populations of the endosymbionts were determined by quantitative PCR. The performance of B. argentifolii and the expressions of essential amino acid biosynthesis genes of P. aleyrodidarum were examined in the first and the tenth generations. The results demonstrated that the populations of P. aleyrodidarum and H. defensa decreased when the whiteflies were transferred to new host plants in the early generations and then restored to the original levels after five to ten generations. In addition, compared with B. argentifolii feeding on cotton for only one generation, the performance of B. argentifolii significantly increased after it fed for ten generations. Since P. aleyrodidarum has nutritional mutualistic relationship with B. argentifolii, we found that the expressions of some essential amino acid biosynthesis genes were regulated during acclimation to cotton. Altogether, the endosymbionts may help B. argentifolii enhance its performance and acclimate to nutrition-inferior and/or more defensive host plants. More understanding of the interactions among B. argentifolii, its endosymbionts, and host plants may strengthen the fundamental knowledge and lead to a novel strategy to control B. argentifolii.