Lin Da-Gin, Jeang Chii-Ling
Department of Food Science, National Chung Hsing University, Taichung, Taiwan, Republic of China.
J Agric Food Chem. 2005 Oct 5;53(20):7958-64. doi: 10.1021/jf050882r.
A novel soluble starch synthase II (SSII) gene was isolated from taro (Colocasia esculenta var. esculenta) tubers. This 2939 bp SSII transcript encodes 804 amino acids with a putative transit peptide of 52 residues. It displays 58-63% identity and 63-69% similarity with SSIIs from other sources. Alignment and phylogenetic analyses showed that taro SSII is more closely related with dicot SSIIs than with the monocot ones, though taro is a monocot. The identification of taro SSII clone as starch synthase was confirmed by the expression of its enzymatic activity in Escherichia coli. Genomic DNA blot analysis revealed a single copy or low number copies of SSII in taro. Expression profile showed that more transcript and protein were accumulated in tubers of 597 +/- 37 g fresh weight, that is, a stage of rapid starch synthesis, than tubers of other stages. By Western blot analysis, SSII was found in both soluble and granule bound portions of tuber extracts, and more SSII protein was found in aged leaves than in leaves of other stages. These results suggest that taro SSII is a novel starch synthase for the synthesis of both transit and storage starch.
从芋头（芋 Colocasia esculenta var. esculenta）块茎中分离出一个新的可溶性淀粉合酶II（SSII）基因。这个2939 bp的SSII转录本编码804个氨基酸，带有一个52个残基的推定转运肽。它与其他来源的SSII有58 - 63%的同一性和63 - 69%的相似性。比对和系统发育分析表明，尽管芋头是单子叶植物，但芋头SSII与双子叶植物的SSII比与单子叶植物的SSII关系更密切。通过在大肠杆菌中表达其酶活性，证实了芋头SSII克隆作为淀粉合酶的身份。基因组DNA印迹分析显示芋头中SSII为单拷贝或低拷贝数。表达谱表明，与其他阶段的块茎相比，在鲜重为597±37 g的块茎（即淀粉快速合成阶段）中积累了更多的转录本和蛋白质。通过蛋白质免疫印迹分析发现，SSII存在于块茎提取物的可溶性部分和颗粒结合部分，且在老叶中发现的SSII蛋白比其他阶段的叶片中更多。这些结果表明，芋头SSII是一种用于合成转运淀粉和贮藏淀粉的新型淀粉合酶。
