Salehuzzaman S N, Jacobsen E, Visser R G
Department of Plant Breeding, Wageningen Agricultural University, Netherlands.
Plant Mol Biol. 1992 Dec;20(5):809-19. doi: 10.1007/BF00027152.
Branching enzyme is involved in the synthesis of amylopectin in plant reserve starch. A cDNA coding for cassava (Manihot esculenta Crantz) branching enzyme was cloned from a lambda gt11 cDNA library using a potato cDNA probe. The cloned cDNA was partially sequenced. The sequence data confirmed the identity of the clone when compared to that of potato, the homology being ca. 80% at the nucleotide level and 85% at the amino acid level. Furthermore, the cloned cassava cDNA was able to restore branching enzyme activity in a branching enzyme deficient Escherichia coli mutant. Results of the Southern analysis suggested that there is a single gene for this particular branching enzyme in the cassava genome. Study of expression patterns by northern hybridization showed that the gene is highly expressed in tubers. The transcript is detectable in stem and petiole, but not in leaves. In roots, the mRNA is hardly present. The expression levels at different stages of tuber growth are similar with exception of very young tubers in which it is relatively low. It is also shown that there is a difference in the level of branching enzyme expression between different cassava genotypes.
分支酶参与植物贮藏淀粉中支链淀粉的合成。使用马铃薯cDNA探针从λgt11 cDNA文库中克隆了编码木薯（Manihot esculenta Crantz）分支酶的cDNA。对克隆的cDNA进行了部分测序。与马铃薯的序列数据相比，序列数据证实了该克隆的身份，核苷酸水平的同源性约为80%，氨基酸水平的同源性约为85%。此外，克隆的木薯cDNA能够恢复分支酶缺陷型大肠杆菌突变体中的分支酶活性。Southern分析结果表明，木薯基因组中存在一个特定分支酶的单一基因。通过Northern杂交研究表达模式表明，该基因在块茎中高度表达。在茎和叶柄中可检测到转录本，但在叶片中未检测到。在根中，几乎不存在mRNA。除了非常幼嫩的块茎中表达水平相对较低外，块茎生长不同阶段的表达水平相似。研究还表明，不同木薯基因型之间分支酶的表达水平存在差异。
