Hattori T, Nakagawa S, Nakamura K
Laboratory of Biochemistry, School of Agriculture, Nagoya University, Japan.
Plant Mol Biol. 1990 Apr;14(4):595-604. doi: 10.1007/BF00027505.
Sporamin, the tuberous root storage protein of the sweet potato, accounts for about 60 to 80% of the total soluble protein of this organ. The amount of sporamin present in other organs is very low, or even not detectable, in the normal field-grown plants. However, the stem of sweet potato plantlets grown axenically on agar medium containing sucrose was found to accumulate large amounts of sporamin. Two-dimensional gel electrophoretic profiles of sporamin precursors synthesized in vitro by poly(A)+ RNA are indistinguishable between tuberous roots of the field-grown plants and stems of the axenically cultured plants, suggesting that an essentially identical set of the members of sporamin multigene family are expressed in these two organs under different growth conditions. Transgenic tobacco plants having a CAT (chloramphenicol acetyltransferase) fusion gene with the 5' upstream region of a sporamin A gene, gSPO-A1, show preferential expression of CAT activity in stems when the plants are maintained in axenic culture on sucrose medium as is the case for sporamin in sweet potato. Deletion analysis revealed that the DNA sequence of gSPO-A1 between -94 and -305, relative to the transcription start site, is important for its expression in tobacco. This region contains two of the previously postulated putative regulatory elements conserved between sporamin A and B genes.
sporamin是甘薯块根中的贮藏蛋白，约占该器官总可溶性蛋白的60%至80%。在正常田间种植的植株中，其他器官中sporamin的含量非常低，甚至检测不到。然而，在含有蔗糖的琼脂培养基上无菌培养的甘薯幼苗茎中，发现积累了大量的sporamin。通过聚腺苷酸加尾RNA体外合成的sporamin前体的二维凝胶电泳图谱，在田间种植植株的块根和无菌培养植株的茎之间没有区别，这表明在不同生长条件下，这两个器官中表达的sporamin多基因家族成员基本相同。具有与sporamin A基因gSPO-A1的5'上游区域融合的CAT（氯霉素乙酰转移酶）基因的转基因烟草植株，当植株在蔗糖培养基上无菌培养时，其茎中CAT活性优先表达，就像甘薯中的sporamin一样。缺失分析表明，相对于转录起始位点，gSPO-A1在-94至-305之间的DNA序列对其在烟草中的表达很重要。该区域包含两个先前假定的sporamin A和B基因之间保守的推定调控元件。
