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標題: | 水稻葉鞘在抽穗期間由儲存組織轉換成供源組織之
分子調控機制 Molecular regulation of sink-source transition in rice leaf sheaths during the heading period |
作者: | Huai-Ju Chen 陳懷如 |
指導教授: | 王淑珍(Shu-Jen Wang) |
關鍵字: | 儲存-供源轉換, sink-source transition, |
出版年 : | 2009 |
學位: | 博士 |
摘要: | 水稻上位葉葉鞘為醣類之暫存組織,其在抽穗前會大量累積澱粉,而在抽穗後其儲存之澱粉會快速分解,並合成蔗糖運送到充實中的穀粒,故在抽穗前後期,葉鞘將由儲存組織轉變成供源組織,此現象稱之葉鞘儲存-供源轉換。為了瞭解葉鞘儲存-供源轉換之分子調控機制,本論文以real-time RT-PCR分析在水稻抽穗期間,葉鞘中澱粉合成、澱粉分解與蔗糖轉運蛋白 (sucrose transporter ; OsSUT)等相關基因之表現變化,結果發現ADP-glucose pyrophosphorylase large subunit 2、granule-bound starch synthase II、soluble starch synthase I、starch branching enzyme (SBE) I、SBEIII及SBEIV等六個澱粉合成相關基因為影響葉鞘澱粉於抽穗前大量累積之主要基因,且其啟動子共同具有受荷爾蒙調控之序列。另一方面,澱粉分解基因α-amylase2A、β-amylase與蔗糖轉運蛋白基因OsSUT1、4在抽穗後表現量會增高,其很有可能分別參與葉鞘在抽穗後時期,澱粉分解及將蔗糖裝載到韌皮部之過程。進一步利用各種荷爾蒙處理水稻切離葉鞘以探討這些基因受荷爾蒙調控之情形,結果發現ABA會抑制AGPase及GBSS之酵素活性,但是會大量促進α-amylase與β-amylase的活性及OsSUT1及 4的基因表現量,顯示ABA可能為影響葉鞘中醣類代謝反應之因子之一。為了篩選參與水稻葉鞘儲存-供源轉換的調控因子,還藉由基因槍暫時性表現系統,分析OsSUT4基因之不同長度啟動子於抽穗前後的表現,鑑定出一段67 bp之啟動子片段,其可能包含控制OsSUT4基因於抽穗後大量表現之重要cis-acting elements。此外,以microarray技術分析抽穗前後之水稻基因組表現變化,發現sucrose synthase、β-D-glucan exohydrolase、sorbitol transporter、ammonium transporter及phosphate transporter等基因也於抽穗前後具有差異性表現,暗示不僅澱粉代謝與蔗糖轉運蛋白基因,還有其他醣類代謝途徑與胺基酸、無機磷之運送亦參與葉鞘儲存-供源之轉變過程。 Upper leaf sheath of rice (Oryza sativa L.) serves as a temporary carbohydrate sink tissue before panicle heading. Starch pre-stored in upper leaf sheaths prior to heading would be remobilized to filling grains at post-heading stage. Thus, upper leaf sheaths could be converted to source tissues from sink tissue during heading period. The process of starch changes in leaf sheath is defined as the sink-source transition. The purpose of this project is to reveal the molecular mechanism of the sink-source transition in rice leaf sheaths during heading period. First, the expression profiles of genes involved in starch synthesis pathway were analyzed and compared to starch content in the second leaf sheath below the flag leaf. The results indicated the changes of ADP-glucose pyrophosphorylase large subunit 2 (AGP-L2), granule-bound starch synthase II (GBSSII), soluble starch synthase I (SSSI), starch branching enzyme (SBE) I, SBEIII, and SBEIV mRNA levels were highly correlated with starch content changes during the heading period in the leaf sheath, and these starch synthesis-related gene promoters shared several common hormone-responsive elements. In addition, the α-amylase2A and β-amylase were considered as major genes that regulated the starch degradation at the post-heading period. Of the five sucrose transporter (OsSUT) genes, OsSUT1 and OsSUT4 appeared to play an important role in sucrose loading into the phloem of source leaf sheaths. Besides, to reveal whether phytohormones were the fac-tors to control the starch metabolism-related enzyme activities and OsSUTs gene ex-pressions, the effects of GA、ABA and BAP on expressions of these enzymes and genes in detached leaf sheaths were examined. The results indicated that not only the expres-sions of OsSUT1 and 4 but the activities of α-amylase and β-amylase can be enhanced by ABA, suggested that ABA is one of the factors to regulate the carbohydrate metabolism in leaf sheaths. Since OsSUT4 gene was significantly up-regulated at post-heading stage, it was used as an indicator gene to identify the molecular mechanism of sink-source transition in leaf sheaths. In order to find the cis-acting elements on OsSUT4 promoter involved in controlling rice leaf sheaths sink-source transition during the heading period, we constructed nine various 5’-deletion OsSUT4 promoter fragments containing GUS reporter gene and analyzed the avtivities by particle bombardment assay. A 67-bp promoter fragment was identified, which might contain important regulatory elements involved in regulation of OsSUT4 gene up-expression in leaf sheath at post-heading stage. Moreover, microarray analysis was also applied to study the mechanism of sink-source transition in leaf sheaths during heading period. The data implied that the dominant processes associated with functional leaf sheath transition from sink to source were not only carbohydrate metabolism but also the translocation of the nitrogen sources and inorganic phosphate. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/9024 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 農藝學系 |
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