Regulation of Gibberellin Biosynthesis in Arabidopsis

赤霉素(GA)是一组植物激素，控制着植物的许多过程和发育事件，如种子萌发、茎生长、开花和果实发育。这些过程通常不是由气体单独控制的，而是由气体与其他激素的相互作用控制的。这项研究将探讨生长素是否能对GA的生物合成起到调节作用，从而为这两种促生长激素之间的相互作用提供一种机制。之前在首席研究员实验室的工作导致了拟南芥突变体(以前称为10.3或GA6)的分离，该突变体降低了茎的生长，推迟了开花，并缩小了果实大小。这些症状可以通过用某种气体处理突变植物来克服，这导致了这样的假设，即该突变株中活性GA激素的生物合成被阻止了。现在已经知道，该突变等位于运输抑制因子3(TIR3)突变，该突变导致生长素的极性运输发生改变。这项拟议的研究将研究生长素是否在GA生物合成途径的两个阶段发挥控制作用，即20-氧化和3b-羟化。由于编码这些生物合成酶的基因已经被克隆，生长素对GA生物合成的可能影响将在基因表达水平上进行研究。通过RNA印迹和报告基因融合，比较这些基因在野生型和TIR3植物中的表达。还将检测改变的生长素反应1(AxR1)突变体，以确定该突变是否也影响编码这些GA生物合成酶的基因的表达。该突变显著降低了植物对生长素的敏感性。最后，野生型植物的生长素状态将受到药理学上的干扰，并将检查对GA反应和GA生物合成酶基因表达的可能影响。这项工作将在圣安东尼奥的德克萨斯大学进行。这所大学的学生大多数是少数民族本科生。该研究计划提供了一个机会，为来自历史上在科学和技术方面代表性不足的本科生提供植物生理学和生物化学实用方面的培训。

The gibberellin (GA) group of plant hormones controls many processes and developmental events in plants, such as seed germination, stem growth, flowering and fruit development. These processes are often not controlled by GAs alone, but by an interplay of GAs with other hormones. The proposed research will investigate whether auxin can exert a regulatory effect on GA biosynthesis, and thus provide one mechanism for cross-talk between these two types of growth promoting hormones. Previous work in the principal investigator's laboratory led to the isolation of a mutant of Arabidopsis thaliana (previously known as 10.3 or ga6) which had reduced stem growth, delayed flowering and reduced fruit size. These symptoms could be overcome by treatment of mutant plants with certain GAs, leading to the hypothesis that biosynthesis of active GA hormone was blocked in this mutant. It has now known that this mutation is allelic to the transport inhibitor3 (tir3) mutation, which leads to an alteration in polar transport of auxin. The proposed research will examine whether auxins exert control at two stages in the GA biosynthetic pathway, namely 20-oxidation and 3b-hydroxylation. Since the genes encoding these biosynthetic enzymes have been cloned, the possible effect of auxins on GA biosynthesis will be examined at the level of gene expression. It is proposed to compare the expression of these genes in wildtype and tir3 plants by RNA blotting, and by using reporter gene fusions. The altered auxin response 1 (axr1) mutant will also be examined to see if this mutation, which dramatically reduces the sensitivity of plants to auxin, also affects the expression of genes encoding these GA biosynthetic enzymes. Finally, the auxin status of wildtype plants will be perturbed pharmacologically, and possible effects on GA response and expression of genes for GA biosynthetic enzymes will be examined.The work will be carried out at the University of Texas at San Antonio. This University is one in which the majority of students are undergraduates from ethnic minorities. The research program presents an opportunity to provide training in practical aspects of plant physiology and biochemistry to undergraduates from groups who are historically under-represented in science and technology.