Yang Lihong, Wang Xiongya, Bai Sufen, Li Xin, Gu Shaohua, Wang Chen-Zhu, Li Xianchun
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China; College of Plant Protection, Henan Agricultural University, Zhengzhou, Henan 450002, China.
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
J Insect Physiol. 2017 Jul;100:21-27. doi: 10.1016/j.jinsphys.2017.05.003. Epub 2017 May 13.
Insect herbivores often secrete glucose oxidase (GOX) onto plants to counteract plant defenses and potential pathogens. Whether generalist herbivores always have significantly higher GOX activities than their specialist counterparts at any comparable stage or conditions and how this is realized remain unknown. To address these two general questions, we subjected larvae of a pair of sister species differed mainly in host range, the generalist Helicoverpa armigera and its specialist counterpart Helicoverpa assulta, to the same sets of stage, protein to digestible carbohydrate (P:C) ratio, allelochemical or host plant treatments for simultaneous analyses of GOX transcripts and activities in their labial glands. GOX activity and transcripts are upregulated concurrently with food ingestion and body growth, downregulated with stopping ingestion and wandering for pupation in both species. The three tested host plants upregulated GOX transcripts, and to a lesser extent, GOX activity in both species. There were significant differences in both GOX transcripts and activity elicited by allelochemicals, but only in GOX transcripts by P:C ratios in both species. GOX activities were higher in H. armigera than H. assulta in all the comparable treatments, but GOX transcripts were significantly higher either in generalists or in specialists, depending on the developmental stages, host plants, P:C ratio and allelochemicals they encounter. These data indicate that the greater GOX activity in generalist herbivores is not achieved by greater transcription rate, but by greater transcript stability, greater translation rate, better enzyme stability and/or their combination.
植食性昆虫常常向植物分泌葡萄糖氧化酶（GOX），以对抗植物防御和潜在病原体。在任何可比阶段或条件下，广食性植食性昆虫的GOX活性是否总是显著高于其专食性同类，以及这是如何实现的，目前仍不清楚。为了解决这两个一般性问题，我们对一对主要在寄主范围上存在差异的姐妹物种的幼虫进行了研究，这对姐妹物种分别是广食性的棉铃虫及其专食性同类烟青虫，我们对它们进行了相同的阶段、蛋白质与可消化碳水化合物比例（P:C）、化感物质或寄主植物处理，以便同时分析它们唇腺中的GOX转录本和活性。在这两个物种中，GOX活性和转录本都随着食物摄取和身体生长而同时上调，随着停止摄取和化蛹前的游走而下调。三种受试寄主植物都上调了这两个物种的GOX转录本，在较小程度上也上调了GOX活性。化感物质引发的GOX转录本和活性都存在显著差异，但两个物种中只有GOX转录本受P:C比例的影响。在所有可比处理中，棉铃虫的GOX活性都高于烟青虫，但GOX转录本在广食性或专食性昆虫中是否显著更高，取决于它们所经历的发育阶段、寄主植物、P:C比例和化感物质。这些数据表明，广食性植食性昆虫中更高的GOX活性并非通过更高的转录速率实现，而是通过更高的转录本稳定性、更高的翻译速率、更好的酶稳定性和/或它们的组合来实现的。
