2003-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/704759摘要：澱粉合成酵素(granule-bound starch synthase I; GBSSI)為合成直鏈澱粉之主要酵素，其在甘藷葉部的表現主要受控於光照。光照經由兩條獨立的途徑影響GBSSI基因之表現，一、光線藉由設定植物內部之生物時鐘，進而促使GBSSI基因的表現呈現概日韻律(circadian rhythm)。二、光照為一間接性的調節者，其藉由光合作用之中間產物，蔗糖(sucrose) ，調控GBSSI基因之表現量。概日韻律(circadian rhythm)的現象普遍存於真核生物。生物時鐘為生物適應環境並協調外在環境訊息與內部生理反應之重要機制，其調控及協調許多參與生理、代謝反應之基因表現，雖然其機制仍不明瞭，但歸納目前之研究結果可知主要有三部分參與生物時鐘的調控，一為環境提供設定生物時鐘之因子，例如光照、溫度。二為生物時鐘本身之組成份。三為生物時鐘下游之訊息傳導分子。 為瞭解植物如何感應外在環境進而利用生物時鐘系統協調澱粉合成，此計畫之主要目標為探討生物時鐘調控GBSSI基因表現之機制，並解析生物時鐘是否擔任一協調光合作用與葉部澱粉合成反應之細胞內在調節者。第一年之計畫主要著重<br> Abstract: Starch granule-bound starch synthase I (GBSSI) gene is the key enzyme for amylose synthesis. Light played a major factor to regulate GBSSI gene expressions in leaves through two independent pathways. First, light induced the circadian expressions of GBSSI gene mediated the biological clock setting, the peak of GBSSI mRNA was at 2 to 4 hr after light was turned on and then decreased gradually. Second, light role an indirect regulator to control the dosage of GBSSI transcripts through the intermediate product of photosynthesis, sucrose, as a direct signal. Circadian rhythms have been observed in several eukaryotes as well as in some prokaryotes. Biological clocks regulate a lot of gene expressions to coordinate metabolic and physiological reactions. Although the molecular mechanism of circadian control was still unclear, three basic components were involved in the regulatory pathway. First, Input signals must be supplied from environments to set or reset biological clocks, and the stimuli usually are light or temperature. Second, circadian clocks that trigger the phenomena of circadian rhythm. Third, output signals to regulate gene expressions or metabolisms. Some of the clock components also functioned as transcriptional factors to regulate circadian transcriptions of other genes. In addition to transcriptional regulation, posttranscriptional mechanisms and protein phosphorylation also played important roles to regulate the circadian rhythm. Circadian rhythm of starch accumulation was observed in sweet potato and spinach leaves. However, the molecular mechanism was still unclear. In sweet potato leaves, light was identified as the input signal to reset the biological clock for circadian regulations of GBSSI gene expressions. In this project, attempts will be made to established the regulatory mechanism of circadian clock controlled-GBSSI expression, and analysis whether the biological clock played as a role to coordinate the metabolic pathway of photosynthesis and starch synthesis. In the first year project, the study will be focused on the identification of the clock-controlled cis-element of GBSSI gene promoter by promoter assay in transgenic Arabidopsis. Besides, the various photoreceptor Arabidopsis mutants will be used to study which photoreceptor played a major role to be a signal receptor to set or reset the biological clock for circadian regulation of GBSSI gene. Second year, the signal transduction pathway of circadian regulation of GBSSI gene will be identified. Therefore, the trans-regulatory elements which bind the clock-controlled cis-element on GBSSI promoter will be studied by yeast one-hybid screen, and its function will be identified by RNAi or antisense techniques. Third year, evaluated whether the circadian clock played an endogenous regulator to control the cooperation of starch synthesis and photosynthesis in leaf tissue. Based on these studies, it will be clear how the circadian clock control the starch synthesis.直鏈澱粉生物時鐘概日韻律澱粉合成酵素甘藷AmyloseBiological clockCircadian rhythmGranule-bound starch synthaseIpomoea batatassweet potato