Chen Hui, Wilkerson Curtis G, Kuchar Jason A, Phinney Brett S, Howe Gregg A
Department of Energy Plant Research Laboratory, Michigan Proteome Consortium, Michigan State University, East Lansing, MI 48824, USA.
Proc Natl Acad Sci U S A. 2005 Dec 27;102(52):19237-42. doi: 10.1073/pnas.0509026102. Epub 2005 Dec 15.
The plant hormone jasmonic acid (JA) activates host defense responses against a broad spectrum of herbivores. Although it is well established that JA controls the expression of a large set of target genes in response to tissue damage, very few gene products have been shown to play a direct role in reducing herbivore performance. To test the hypothesis that JA-inducible proteins (JIPs) thwart attack by disrupting digestive processes in the insect gut, we used a MS-based approach to identify host proteins that accumulate in the midgut of Manduca sexta larvae reared on tomato (Solanum lycopersicum) plants. We show that two JIPs, arginase and threonine deaminase (TD), act in the M. sexta midgut to catabolize the essential amino acids Arg and Thr, respectively. Transgenic plants that overexpress arginase were more resistant to M. sexta larvae, and this effect was correlated with reduced levels of midgut Arg. We present evidence indicating that the ability of TD to degrade Thr in the midgut is enhanced by herbivore-induced proteolytic removal of the enzyme's C-terminal regulatory domain, which confers negative feedback regulation by isoleucine in planta. Our results demonstrate that the JA signaling pathway strongly influences the midgut protein content of phytophagous insects and support the hypothesis that catabolism of amino acids in the insect digestive tract by host enzymes plays a role in plant protection against herbivores.
植物激素茉莉酸（JA）可激活宿主针对多种食草动物的防御反应。尽管已有充分证据表明JA可响应组织损伤调控大量靶基因的表达，但很少有基因产物被证明在降低食草动物的取食能力方面发挥直接作用。为了验证茉莉酸诱导蛋白（JIPs）通过破坏昆虫肠道消化过程来抵御攻击这一假说，我们采用基于质谱的方法来鉴定在以番茄（Solanum lycopersicum）植株饲养的烟草天蛾幼虫中肠中积累的宿主蛋白。我们发现两种JIPs，即精氨酸酶和苏氨酸脱氨酶（TD），分别在烟草天蛾中肠中发挥作用，分解必需氨基酸精氨酸（Arg）和苏氨酸（Thr）。过量表达精氨酸酶的转基因植物对烟草天蛾幼虫的抗性更强，且这种效应与中肠中Arg水平的降低相关。我们提供的证据表明，食草动物诱导的蛋白水解作用去除了该酶的C端调节结构域，从而增强了TD在中肠中降解Thr的能力，该调节结构域在植物中通过异亮氨酸赋予负反馈调节。我们的结果表明，JA信号通路强烈影响植食性昆虫的中肠蛋白质含量，并支持宿主酶在昆虫消化道中对氨基酸的分解代谢在植物抵御食草动物方面发挥作用这一假说。
