Friedrich L, Vernooij B, Gaffney T, Morse A, Ryals J
Agricultural Biotechnology, Ciba-Geigy Corporation, Research Triangle Park, NC 27709-2257, USA.
Plant Mol Biol. 1995 Dec;29(5):959-68. doi: 10.1007/BF00014969.
Transgenic tobacco plants that express the bacterial nahG gene encoding salicylate hydroxylase have been shown to accumulate very little salicylic acid and to be defective in their ability to induce systemic acquired resistance (SAR). In recent experiments using transgenic NahG tobacco and Arabidopsis plants, we have also demonstrated that salicylic acid plays a central role in both disease susceptibility and genetic resistance. In this paper, we further characterize tobacco plants that express the salicylate hydroxylase enzyme. We show that tobacco mosaic virus (TMV) inoculation of NahG tobacco leaves induces the accumulation of the nahG mRNA in the pathogen infected leaves, presumably due to enhanced stabilization of the bacterial mRNA. SAR-associated genes are expressed in the TMV-infected leaves, but this is localized to the area surrounding necrotic lesions. Localized acquired resistance (LAR) is not induced in the TMV-inoculated NahG plants suggesting that LAR, like SAR, is dependent on SA accumulation. When SA is applied to nahG-expressing leave's SAR gene expression does not result. We have confirmed earlier reports that the salicylate hydroxylase enzyme has a narrow substrate specificity and we find that catechol, the breakdown product of salicylic acid, neither induces acquired resistance nor prevents the SA-dependent induction of the SAR genes.
已证明，表达编码水杨酸羟化酶的细菌nahG基因的转基因烟草植株积累的水杨酸极少，且诱导系统获得性抗性（SAR）的能力存在缺陷。在最近使用转基因NahG烟草和拟南芥植株进行的实验中，我们还证明了水杨酸在感病性和遗传抗性中都起着核心作用。在本文中，我们进一步对表达水杨酸羟化酶的烟草植株进行了表征。我们发现，用烟草花叶病毒（TMV）接种NahG烟草叶片会诱导nahG mRNA在受病原体感染的叶片中积累，这可能是由于细菌mRNA的稳定性增强所致。与SAR相关的基因在受TMV感染的叶片中表达，但这局限于坏死斑周围的区域。在接种TMV的NahG植株中未诱导出局部获得性抗性（LAR），这表明LAR与SAR一样，依赖于SA的积累。当将SA施用于表达nahG的叶片时，不会导致SAR基因表达。我们证实了早期的报道，即水杨酸羟化酶具有狭窄的底物特异性，并且我们发现水杨酸的分解产物儿茶酚既不诱导获得性抗性，也不阻止SAR基因的SA依赖性诱导。
