赤霉素(gibberellins, GA)是植物激素之一,调控植物生长和发育。植物体中赤霉素合成量直接影响植物的形态和生物量。在赤霉素合成途径中,柯巴基焦磷酸合酶基因(copalyl diphosphate synthase, CPS)是第一个合酶基因,该基因突变会严重影响赤霉素合成量。本研究通过对根和下胚轴缩短、晚花、丛生、矮化的拟南芥(Arabidopsis thaliana)突变体ga1-168进行图位克隆,鉴定出AtCPS的一个等位基因AtCPS-168。该等位基因的突变位点是AtCPS基因的第2768位核苷酸,鸟嘌呤(G)突变为腺嘌呤(A),导致AtCPS蛋白萜类合酶(Terpene_synth)结构域中的第326位缬氨酸(V)突变成蛋氨酸(M)。通过等位分析确定AtCPS-168是AtCPS的等位基因。遗传互补实验显示AtCPS V326M突变导致植物丛生、矮化等发育缺陷表型。赤霉素含量测定结果证明AtCPS V326M突变导致赤霉素的合成量减少。外施赤霉素实验结果表明,外施赤霉素能恢复拟南芥突变体ga1-168赤霉素合成量降低导致的植株丛生、矮化等发育缺陷表型。因此,本研究为通过定点突变赤霉素合成酶基因的特定位点改变赤霉素含量来塑造植物理想株高和株型提供理论指导。

Gibberellins are a class of typical phytohormones, which regulate plant growth and development. The contents of gibberellins dramatically affect the morphology and biomass of plant. The encoding protein of copalyl diphosphate synthase gene (CPS) catalyzes the first-step in the biosynthetic pathway of gibberellins. The mutation in this gene may significantly affect the contents of gibberellins in plants. In this study, we found an EMS-triggered mutant, ga1-168, showing short roots, short hypocotyls, late flowering and dwarf. Map-based cloning revealed that the causal gene of ga1-168 was AtCPS-168, an allele of AtCPS gene. The encoding protein of AtCPS-168 was AtCPS V326M which was resulted from a single-point mutation (guanine to adenine at nucleotide 2768) of AtCPS gene. Protein domain analysis showed that V326 was located in the Terpene_synth domain. The allelism test demonstrated that AtCPS-168 was an allele of AtCPS gene. The transgenic complementation of ga1-168 indicated that AtCPS V326M led to the dwarf and bushy phenotype of ga1-168. The endogenous gibberellins contents analysis suggested that the gibberellins contents of ga1-168 were much lower than that of wild-type. The exogenous GA₃ application assay uncovered that application of GA₃ can complement the dwarf and bushy phenotype of ga1-168 caused by low endogenous gibberellins contents. Therefore, this study suggested that it is an elegant way to create the ideal plant architecture and height by site-directed mutating the gibberellin biosynthetic genes.