Caterpillar herbivory and salivary enzymes decrease transcript levels of Medicago truncatula genes encoding early enzymes in terpenoid biosynthesis
Caterpillar herbivory and salivary enzymes decrease transcript levels of Medicago truncatula genes encoding early enzymes in terpenoid biosynthesis
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DOI：
10.1007/s11103-005-4923-y
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发表时间：
2006-03-01
影响因子：
5.1
通讯作者：
Korth, KL
中科院分区：
文献类型：
--
作者：
Bede, JC;Musser, RO;Korth, KL
作为对毛虫食草性的反应，紫花苜蓿和相关植物通过诱导皂素和挥发性萜类化合物的生物合成来保护自己。这两种类型的防御性化合物都来自代谢中间体异戊烯基二磷酸(IPP)。在植物中，有两条不同的生物合成途径可以产生IPP：胞质甲氧戊酸途径和与叶绿体相关的2C-甲基赤藓糖醇4-磷酸(MEP)途径。在紫花苜蓿中，甜菜夜蛾对幼虫食草性的反应，测定了在这些生物合成途径的早期步骤中活跃的关键调控基因的转录水平。在毛虫为害的叶片中，两个萜类途径早期阶段的酶编码转录本都较低。更高程度的食草动物危害加剧了转录水平的下降；然而，转录数量不受昆虫幼虫阶段的影响。昆虫幼虫被操纵以减少唇腺唾液分泌，用来检验唾液激发子在调节基因表达中的作用。结果表明，昆虫唾液因子，可能是葡萄糖氧化酶(GOX)，可能与草食后转录水平的降低有关。在机械损伤的叶子中添加GOX或过氧化氢证实了这些发现。相比之下，编码可能的萜烯合酶的基因的转录水平在机械或虫害的叶片中被诱导。这些数据表明，昆虫唾液因子可以抑制参与植物防御途径的基因的转录水平。研究结果还表明，对昆虫食草性等压力的反应，调节发生在MEP途径的早期步骤。
In response to caterpillar herbivory, alfalfa and related plant species defend themselves through the induction of saponin and volatile terpenoid biosynthesis. Both these types of defensive compounds are derived from the metabolic intermediate, isopentenyl diphosphate (IPP). In plants, two distinct biosynthetic pathways can generate IPP; the cytosolic mevalonate pathway and the plastid-associated 2C-methyl erythritol 4-phosphate (MEP) pathway. In Medicago truncatula, transcript levels of key regulatory genes active in the early steps of these biosynthetic pathways were measured in response to larval herbivory by the beet armyworm, Spodoptera exigua. Transcripts encoding enzymes at early steps of both terpenoid pathways were lower in caterpillar-damaged leaves. Higher degrees of herbivore damage accentuated the decrease in transcript levels; however, transcript amounts were not affected by insect larval stage. Insect larvae, manipulated to reduce labial gland salivary secretions, were used to examine the role of the salivary elicitors in modulating gene expression. Results suggest that an insect salivary factor, possibly glucose oxidase (GOX), may be involved in reduction of transcript levels following herbivory. Addition of GOX or hydrogen peroxide to mechanically wounded leaves confirm these findings. In comparison, transcript levels of a gene encoding a putative terpene synthase are induced in mechanically- or insect-damaged leaves. These data show that insect salivary factors can act to suppress transcript levels of genes involved in plant defense pathways. Findings also suggest that in response to stress such as insect herbivory, regulation occurs at the early steps of the MEP pathway.