糜子SAMS基因的克隆及其在干旱复水中的表达模式分析

以糜子抗旱节水研究中获得的一个与S-腺苷甲硫氨酸合成酶(SAMS)基因同源性较高的EST序列为基础, 采用RT-PCR技术从糜子中分离到一个SAMS基因的全长cDNA序列(命名为PmSAMS), 全长1 293 bp, 编码396个氨基酸, 具有SAMS典型的N端结构域、中间结构域及C端结构域。糜子、马铃薯、拟南芥、甜菜、大麦、荔枝、番茄和水稻8种植物SAMS的氨基酸序列多重比较分析表明, 不同植物的SAMS的氨基酸相似程度非常高(92%~97%), 其中糜子与水稻的相似性最高(97%), 说明SAMS基因在植物进化中非常保守。PmSAMS基因在糜子幼苗干旱及复水过程中的半定量RT-PCR表达模式分析表明, 在干旱早期(土壤含水量36%)诱导该基因大量表达, 而干旱程度更严重时(土壤含水量为24%)其表达受到严重抑制, 表达量比对照还低; 严重干旱后复水2 h, 其表达量增强至干旱早期的表达量, 而复水6 h后表达量降低至对照(干旱处理前)水平。可见, PmSAMS基因的表达涉及糜子响应干旱胁迫及干旱后复水过程, 可能是糜子抗旱节水的关键基因。该基因的克隆为进一步探讨其应用于农作物抗旱节水性的遗传改良奠定了基础。

Cloning of A S-Adenosylmethionine Synthetase Gene from Broomcorn Millet (Panicum miliaceum L.) and Its Expression during Drought and Re-Watering

To explore more genes for the improvement of drought-tolerance and water use efficiency in plants, broomcorn millet (Panicum miliaceum L.) was used to investigate the differential gene expression during drought stress and re-watering after serious drought stress by constructing SSH-cDNA library in previous study. A full-length cDNA of S-adenosylmethionine synthetase (SAMS) gene was amplified from broomcorn millet using PCR. The PCR primers were designed based on an EST sequence highly similar to SAMS gene in the SSH-cDNA library and the sequences of SAMS genes from rice and barley. The full-length cDNA sequence of SAMS gene amplified from broomcorn millet was 1 293 bp in length and designated as PmSAMS, encoding 396 amino acids with the 3 typical domains of SAMS (N terminal domain, inter domain and C terminal domain). Multiple alignment analysis based on the amino acids encoded by some SAMS genes from broomcorn millet (P. miliaceum L.), potato (S. tuberosum), Arabidopsis (A. thaliana), sugar beet (B. vulgaris), barley (H. vulgare), litchi (L. chinensis), tomato (L. esculentum), and rice (O. sativa) indicated that SAMS was very conserved among different species of plants with 92–97% of sequence similarity of amino acids, and PmSAMS had the highest similarity with that of rice (97%). The expression patterns of PmSAMS during drought and re-watering after serious drought were investigated by means of semi-quantitative RT-PCR. The results showed that the ex-pressions of PmSAMS were great at the beginning of drought treatment (soil relative moisture of 36%), then declined under seri-ous drought (soil relative moisture of 24%) to less than the normal level, and increased at 2 h after re-watering, declined to the normal level at 6 h after re-watering. The expression patterns of PmSAMS during drought and re-watering after serious drought indicated that it was involved in the response of broomcorn millet to drought and re-watering and might be one of the key genes for drought tolerance and water use efficiency of broomcorn millet. The cloning of this gene provides the potential for its utiliza-tion in the improvement of drought-tolerance and water use efficiency in other plants.