Wang Xuelu, Lopez-Valenzuela Jose A, Gibbon Bryan C, Gakiere Bertrand, Galili Gad, Larkins Brian A
Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA.
J Exp Bot. 2007;58(10):2653-60. doi: 10.1093/jxb/erm100. Epub 2007 Jun 1.
A quantitative trait locus has previously been identified in maize (Zea mays L.) that influences the level of free amino acids in the endosperm, especially those from the aspartate pathway: lysine, threonine, methionine, leucine, and isoleucine. Because this locus occurs in a region of the genome containing ask2, a monofunctional aspartate kinase, the nature of the monofunctional aspartate kinase genes in the parental inbreds, Oh545o2 and Oh51Ao2, was investigated. Two genes, Ask1 and Ask2 were isolated, and Ask2 was mapped to the ask2 locus. Nucleotide sequence analysis of the Ask2 alleles from Oh545o2 and Oh51Ao2 showed they differ by one amino acid. Both alleles complemented a yeast aspartate kinase mutant, hom3, and based on the growth of the yeast mutant it appeared that Ask2-Oh545o2 produces an enzyme with greater total activity than that encoded by the Oh51Ao2 allele. The results suggest that the higher level of free amino acids derived from the aspartate pathway in Oh545o2 endosperm results from a single amino acid change in the ASK2 enzyme that has pleiotropic effects on its activity.
此前已在玉米（Zea mays L.）中鉴定出一个数量性状基因座，它会影响胚乳中游离氨基酸的水平，尤其是来自天冬氨酸途径的氨基酸：赖氨酸、苏氨酸、蛋氨酸、亮氨酸和异亮氨酸。由于该基因座位于基因组中包含单功能天冬氨酸激酶ask2的区域，因此对亲本自交系Oh545o2和Oh51Ao2中的单功能天冬氨酸激酶基因的性质进行了研究。分离出了两个基因Ask1和Ask2，并将Ask2定位到ask2基因座。对Oh545o2和Oh51Ao2的Ask2等位基因进行核苷酸序列分析表明，它们相差一个氨基酸。两个等位基因均能互补酵母天冬氨酸激酶突变体hom3，基于酵母突变体的生长情况，似乎Ask2 - Oh545o2产生的酶的总活性比Oh51Ao2等位基因编码的酶更高。结果表明，Oh545o2胚乳中天冬氨酸途径衍生的游离氨基酸水平较高是由于ASK2酶中的单个氨基酸变化对其活性产生了多效性影响。
