McConn M, Creelman R A, Bell E, Mullet J E, Browse J
Institute of Biological Chemistry, Washington State University, P.O. Box 646340, Pullman, WA 99164-6340, USA.
Proc Natl Acad Sci U S A. 1997 May 13;94(10):5473-7. doi: 10.1073/pnas.94.10.5473.
The signaling pathways that allow plants to mount defenses against chewing insects are known to be complex. To investigate the role of jasmonate in wound signaling in Arabidopsis and to test whether parallel or redundant pathways exist for insect defense, we have studied a mutant (fad3-2 fad7-2 fad8) that is deficient in the jasmonate precursor linolenic acid. Mutant plants contained negligible levels of jasmonate and showed extremely high mortality ( approximately 80%) from attack by larvae of a common saprophagous fungal gnat, Bradysia impatiens (Diptera: Sciaridae), even though neighboring wild-type plants were largely unaffected. Application of exogenous methyl jasmonate substantially protected the mutant plants and reduced mortality to approximately 12%. These experiments precisely define the role of jasmonate as being essential for the induction of biologically effective defense in this plant-insect interaction. The transcripts of three wound-responsive genes were shown not to be induced by wounding of mutant plants but the same transcripts could be induced by application of methyl jasmonate. By contrast, measurements of transcript levels for a gene encoding glutathione S-transferase demonstrated that wound induction of this gene is independent of jasmonate synthesis. These results indicate that the mutant will be a good genetic model for testing the practical effectiveness of candidate defense genes.
已知植物抵御咀嚼式昆虫的信号通路很复杂。为了研究茉莉酸在拟南芥伤口信号传导中的作用，并测试是否存在针对昆虫防御的平行或冗余通路，我们研究了一种茉莉酸前体亚麻酸缺乏的突变体（fad3-2 fad7-2 fad8）。突变体植株中茉莉酸含量可忽略不计，并且受到常见腐食性真菌蚋（Bradysia impatiens，双翅目：Sciaridae）幼虫攻击后死亡率极高（约80%），即便相邻的野生型植株基本未受影响。施加外源茉莉酸甲酯可显著保护突变体植株，并将死亡率降至约12%。这些实验精确地确定了茉莉酸在这种植物 - 昆虫相互作用中诱导生物有效防御方面的关键作用。研究表明，三个伤口响应基因的转录本不会因突变体植株受伤而被诱导，但施加茉莉酸甲酯可诱导相同的转录本。相比之下，对编码谷胱甘肽S-转移酶的基因转录水平的测量表明，该基因的伤口诱导与茉莉酸合成无关。这些结果表明，该突变体将是测试候选防御基因实际有效性的良好遗传模型。
