Wilkinson J Q, Crawford N M
Department of Biology, University of California, San Diego, La Jolla 92093-0116.
Mol Gen Genet. 1993 May;239(1-2):289-97. doi: 10.1007/BF00281630.
Mutant plants defective in the assimilation of nitrate can be selected by their resistance to the herbicide chlorate. In Arabidopsis thaliana, mutations at any one of nine distinct loci confer chlorate resistance. Only one of the CHL genes, CHL3, has been shown genetically to be a nitrate reductase (NR) structural gene (NIA2) even though two NR genes (NIA1 and NIA2) have been cloned from the Arabidopsis genome. Plants in which the NIA2 gene has been deleted retain only 10% of the wild-type shoot NR activity and grow normally with nitrate as the sole nitrogen source. Using mutagenized seeds from the NIA2 deletion mutant and a modified chlorate selection protocol, we have identified the first mutation in the NIA1 NR structural gene. nia1, nia2 double mutants have only 0.5% of wild-type shoot NR activity and display very poor growth on media with nitrate as the only form of nitrogen. The nia1-1 mutation is a single nucleotide substitution that converts an alanine to a threonine in a highly conserved region of the molybdenum cofactor-binding domain of the NR protein. These results show that the NIA1 gene encodes a functional NR protein that contributes to the assimilation of nitrate in Arabidopsis.
可以通过对除草剂氯酸盐的抗性来筛选在硝酸盐同化方面存在缺陷的突变植物。在拟南芥中，九个不同位点中任何一个位点发生突变都会赋予氯酸盐抗性。尽管已经从拟南芥基因组中克隆出两个硝酸还原酶（NR）基因（NIA1和NIA2），但只有一个CHL基因CHL3在遗传学上被证明是硝酸还原酶（NR）结构基因（NIA2）。NIA2基因被删除的植物仅保留野生型地上部分NR活性的10%，并以硝酸盐作为唯一氮源正常生长。利用NIA2缺失突变体的诱变种子和改良的氯酸盐筛选方案，我们鉴定出了NIA1 NR结构基因中的首个突变。nia1、nia2双突变体仅具有野生型地上部分NR活性的0.5%，并且在以硝酸盐作为唯一氮源形式的培养基上生长非常差。nia1 - 1突变是一个单核苷酸替换，它在NR蛋白的钼辅因子结合结构域的高度保守区域将一个丙氨酸转变为苏氨酸。这些结果表明，NIA1基因编码一种功能性NR蛋白，该蛋白有助于拟南芥中的硝酸盐同化。
