Studies on the gene expression and physiological functions of sucrose synthase isozymes in green bamboo Bambusa oldhamii

• Main Authors: Wen-Bin Chiu, 邱文彬
• Other Authors: 王愛玉
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/20237736058156799605

博士 === 國立臺灣大學 === 微生物與生化學研究所 === 96 === Bamboo is distinguished by its rapid growth. Research on the green bamboo Bambusa oldhamii has suggested that sucrose synthase (SuS), which catalyzes the reversible conversion of sucrose and UDP into UDP-glucose and fructose, is important in providing substrates for the highly active synthesis of cell wall polysaccharides in growing shoots and young culm. The objective of this study is to elucidate the role of SuS in bamboo growth. Four SuS cDNA clones (BoSus1, BoSus2, BoSus3 and BoSus4) isolated from a cDNA library of etiolated bamboo shoots were characterized by sequences analysis and Southern analysis. Northern analysis, semi-quantitative RT-PCR, immunohistochemical analysis and in situ RT-PCR were used for investigating the expression patterns of each gene in bamboo shoots at various growth stages and in various tissues. In addition, recombinant BoSuS proteins were produced in Escherichia coli and purified by immobilized metal affinity chromatography for functional identification. BoSus1 and BoSus3 may be duplicate or homeologous genes, the sequences of which show high identity. Similarly, BoSus2 shows high identity with BoSus4. Kinetic analysis showed that the two BoSuS isoforms of each type had similar Michaelis constant (Km) values for sucrose, but different values for UDP. Northern analysis and semi-quantitative RT-PCR showed that the four genes were expressed in various bamboo organs but were differentially regulated. Immunohistochemical analysis using polyclonal and monoclonal antibodies against rice SuS revealed that BoSuS was widely distributed in different tissues of unexpanded leaf. In etiolated shoot and leaf sheath, BoSuS was detected in the parenchyma cells and vascular tissues. In mature leaves, SuS was located in epidermal cells, mesophyll and vascular tissues. In situ RT-PCR analysis showed that the four BoSuS were all expressed in parenchyma cells of leaf sheath and all part of etiolated shoot. The BoSus2 has significant differential expression patterns in the middle and top regions of etiolated shoots. In sink leaf (unexpanded leaf) and mature leaf, the four BoSus gene were also differentially expressed but exhibited similar expression pattern in leaf sheath. The results underscore the roles of SuS in sucrose loading/unloading in both source and sink organs. Multiple BoSuS isoforms play a variety of important roles in green bamboo, directing translocated carbon towards both the polysaccharide biosynthesis and energy production necessary to support the rapid growth of bamboo.