小金海棠S-腺苷甲硫氨酸合成酶基因（MxSAMS）的克隆和表达分析

从本实验室建立的小金海棠缺铁差减文库中分离出一个cDNA片段，在GenBank中发现该片段与其它植物的S-腺苷甲硫氨酸合成酶(SAMS)基因具有90%的同源性。利用RACE技术成功地获得小金海棠（Malus xiaojinensis）SAMS基因(MxSAMS)的cDNA全长序列（GenBank登录号：EU639408），该基因cDNA全长1 479 bp，最大开放阅读框1 176 bp，编码392个氨基酸，酶蛋白理论分子量为42.99 kD；与其它植物的蛋白质氨基酸序列同源性在88.1%~92.6%之间。推测的MxSAMS蛋白质三级结构包含3个保守结构域和一个保守的ATP结合位点GAGDQG。Southern 杂交显示，MxSAMS基因在小金海棠基因组中是单拷贝的。半定量RT-PCR结果表明，该基因在小金海棠的根和叶中均受缺铁胁迫诱导增强表达。

Cloning of S-adenosylmethionine Synthetase Gene from Malus xiaojinensis (MxSAMS) and Its Expression under Iron-deficiency Stress

S-adenosylmethionine synthetase gene (SAMS) cDNA from a iron-deficiency subtracted library of Malus xiaojinensis was isolated ,which showed 90% identity to the other homolog gene of S-adenolyl-L-methionine synthetase enzyme in GenBank. The full length cDNA of SAMS gene from M. xiaojinensis was obtained using RACE and named as MxSAMS (GenBank accession No.EU639408). The full cDNA of MxSAMS was 1 479 bp with an open reading frame of including a complete ORF of 1 176 bp that encoded a predicted polypeptide of 392 amino acids with the predicted MW of 42.99 kD. MxSAMS showed 88.1%～92.6% amino acids sequence similarity with the other SAMS in plant. The deduced product of MxSAMS had the conserved domain among all the known SAMS, including a ATP binding domain. Southern blot showed that there was only one single copy of MxSAMS gene in the genome. The result of semiquantitative RT-PCR indicated that the MxSAMS in root and leaves of M. xiaojinensis was induced by iron-deficiency stress.