Department of Plant Sciences, University of Tennessee, Knoxville, TN, USA.
Plant Biotechnol J. 2013 Dec;11(9):1135-45. doi: 10.1111/pbi.12108. Epub 2013 Aug 23.
Salicylic acid plays a critical role in activating plant defence responses after pathogen attack. Salicylic acid methyltransferase (SAMT) modulates the level of salicylic acid by converting salicylic acid to methyl salicylate. Here, we report that a SAMT gene from soybean (GmSAMT1) plays a role in soybean defence against soybean cyst nematode (Heterodera glycines Ichinohe, SCN). GmSAMT1 was identified as a candidate SCN defence-related gene in our previous analysis of soybean defence against SCN using GeneChip microarray experiments. The current study started with the isolation of the full-length cDNAs of GmSAMT1 from a SCN-resistant soybean line and from a SCN-susceptible soybean line. The two cDNAs encode proteins of identical sequences. The GmSAMT1 cDNA was expressed in Escherichia coli. Using in vitro enzyme assays, E. coli-expressed GmSAMT1 was confirmed to function as salicylic acid methyltransferase. The apparent Km value of GmSAMT1 for salicylic acid was approximately 46 μM. To determine the role of GmSAMT1 in soybean defence against SCN, transgenic hairy roots overexpressing GmSAMT1 were produced and tested for SCN resistance. Overexpression of GmSAMT1 in SCN-susceptible backgrounds significantly reduced the development of SCN, indicating that overexpression of GmSAMT1 in the transgenic hairy root system could confer resistance to SCN. Overexpression of GmSAMT1 in transgenic hairy roots was also found to affect the expression of selected genes involved in salicylic acid biosynthesis and salicylic acid signal transduction.
水杨酸在植物受到病原体攻击后激活防御反应中起着关键作用。水杨酸甲基转移酶（SAMT）通过将水杨酸转化为甲基水杨酸来调节水杨酸的水平。在这里，我们报告来自大豆的 SAMT 基因（GmSAMT1）在大豆对大豆胞囊线虫（Heterodera glycines Ichinohe，SCN）的防御中发挥作用。在我们之前使用基因芯片实验分析大豆对 SCN 的防御时，GmSAMT1 被鉴定为候选 SCN 防御相关基因。本研究从抗 SCN 大豆品系和感 SCN 大豆品系中分离了全长 GmSAMT1 cDNA。这两个 cDNA 编码的蛋白质具有相同的序列。GmSAMT1 cDNA 在大肠杆菌中表达。通过体外酶测定，证实大肠杆菌表达的 GmSAMT1 具有水杨酸甲基转移酶的功能。GmSAMT1 对水杨酸的表观 Km 值约为 46 μM。为了确定 GmSAMT1 在大豆对 SCN 的防御中的作用，产生了过表达 GmSAMT1 的转基因毛状根并对其抗 SCN 性进行了测试。在感 SCN 的背景下过表达 GmSAMT1 显著降低了 SCN 的发育，表明在转基因毛状根系统中过表达 GmSAMT1 可以赋予对 SCN 的抗性。还发现过表达 GmSAMT1 会影响参与水杨酸生物合成和水杨酸信号转导的选定基因的表达。
