Effects of double mutation of the waxy and amylose-extender genes on gene expression profiles and metabolites in rice
Tez Türü: Doktora
Tezin Yürütüldüğü Kurum: Osaka Prefectural University, Graduate School of Life and Environmental Science, Life Science , Japonya
Tez Danışmanı: Shınıchı Kıtamura
Tezin Onay Tarihi: 2011
Tezin Dili: İngilizce
Desteklendiği Program: Diğer
Özet:
Rice (Oryza sativa) is the staple food for billions of people. In addition to its agronomic importance, rice is also an important biological model species for monocot plants. The International Rice Genome Sequencing Project has finished sequencing the rice genome. To date, more than 30,000 full-length cDNA sequences of Oryza sativa have been deposited in a publicly available database. This database offers a complete overview to understand the biological functions of the genes. At this time, gene expression analysis comprises one of the most important areas of gene function studies.
Starch is the reserved carbohydrate form produced in the cereal’s endosperm. Starch granules consist of two types of glucose polymers: mainly linear amylose in which D-glucosyl units are linked with α-1,4 glucosidic bonds and a few branches of α-1,6 linkages, and amylopectin which is a highly branched molecule consisting of short amylose chains connected with α-1,6 linkages. Starch is synthesized in the amyloplast of the endosperm cells by the coordinated action of a group of enzymes. Amylose is synthesized by ADP glucose pyrophosphorylase (AGPase) and granule-bound starch synthase (GBSSI), while amylopectin is synthesized by AGPase, starch synthase (SS), starch branching enzyme (SBE) and starch debranching enzyme (DBE). Mutations in the genes involved in starch synthesis result in not only altered starch structures, but also changes in grain composition and gene expression profile. Waxy (wx) protein, encoded by GBSSI, is responsible for amylose synthesis in the rice endosperm. The loss of GBSSI activity by mutation results in amylose-free (waxy, wx) starch phenotypes. Starch-branching enzymes (SBE) play an essential role in the synthesis of amylopectin. Mutation in the gene for SBEIIb results in high amylose (amylose extender, ae) starch phenotypes.
A series of studies were conducted on the effect of the loss of activity of GBSSI and SBEIIb on grain composition, amylopectin fine structure and gene expression levels in the developing rice endosperm.