Silverstone A L, Chang C, Krol E, Sun T P
Department of Botany, Duke University, Durham, NC 27708-1000, USA.
Plant J. 1997 Jul;12(1):9-19. doi: 10.1046/j.1365-313x.1997.12010009.x.
The GA1 gene of Arabidopsis thaliana encodes ent-kaurene synthase A (KSA), which catalyzes the first committed step in the biosynthetic pathway of the plant hormone gibberellin (GA). Its location in the GA biosynthetic pathway has led to speculation that KSA regulation is one of the controlling steps. However, because KSA activity is so low that it is only measurable in Arabidopsis siliques, GA1 promoter-GUS reporter gene fusions and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) were used to examine the expression pattern of GA1. The results from this study indicate that GA1 gene expression is highly regulated during growth and development, and it is restricted to specific cell types at the sites of expression. GA1 promoter activity is highest in rapidly growing tissues, e.g. shoot apicas, root tips, developing flowers and seeds. It is also active in the vascular tissue of some non-growing organs, such as expanded leaves, suggesting that these leaves may be a site of GA synthesis for transport to other organs. It was also found that the first one or two introns in the GA1 gene are required for proper expression. Because of the high degree of regulation, GA1 may act as a gatekeeper, controlling the flow of metabolites into the GA biosynthetic pathway, while the levels of specific bioactive GAs are controlled by other downstream steps.
拟南芥的GA1基因编码内贝壳杉烯合酶A（KSA），它催化植物激素赤霉素（GA）生物合成途径中的第一个关键步骤。其在GA生物合成途径中的位置引发了一种推测，即KSA调控是控制步骤之一。然而，由于KSA活性非常低，仅在拟南芥角果中可检测到，因此使用GA1启动子-GUS报告基因融合以及定量逆转录聚合酶链反应（RT-PCR）来检测GA1的表达模式。这项研究的结果表明，GA1基因表达在生长和发育过程中受到高度调控，并且在表达位点仅限于特定细胞类型。GA1启动子活性在快速生长的组织中最高，例如茎尖、根尖、发育中的花和种子。它在一些非生长器官的维管组织中也有活性，如展开的叶片，这表明这些叶片可能是GA合成并运输到其他器官的场所。还发现GA1基因中的前一两个内含子对于正常表达是必需的。由于高度的调控，GA1可能充当一个守门人，控制代谢物进入GA生物合成途径的流量，而特定生物活性GA的水平则由其他下游步骤控制。
