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首页> 美国卫生研究院文献>Plant Physiology >Maize Starch-Branching Enzyme Isoforms and Amylopectin Structure. In the Absence of Starch-Branching Enzyme IIb, the Further Absence of Starch-Branching Enzyme Ia Leads to Increased Branching
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Maize Starch-Branching Enzyme Isoforms and Amylopectin Structure. In the Absence of Starch-Branching Enzyme IIb, the Further Absence of Starch-Branching Enzyme Ia Leads to Increased Branching

机译：玉米淀粉分支酶同工型和支链淀粉结构。在缺乏淀粉分支酶IIb的情况下，进一步缺乏淀粉分支酶Ia会导致分支增加

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Previous studies indicated that the deficiency of starch-branching enzyme (SBE) Ia in the single mutant sbe1a∷Mu (sbe1a) has no impact on endosperm starch structure, whereas the deficiency of SBEIIb in the ae mutant is well known to reduce the branching of starch. We hypothesized that in maize (Zea mays) endosperm, the function of SBEIIb is predominant to that of SBEIa, and SBEIa would have an observable effect only on amylopectin structure in the absence of SBEIIb. To test this hypothesis, the mutant sbe1a was introgressed into lines containing either wx (lacking the granule-bound starch synthase GBSSI) or ae wx (lacking both SBEIIb and GBSSI) in the W64A background. Both western blotting and zymogram analysis confirmed the SBEIa deficiency in sbe1a wx and sbe1a ae wx, and the SBEIIb deficiency in ae wx and sbe1a ae wx. Using zymogram analysis, no pleiotropic effects of sbe1a genes on SBEIIa, starch synthase, or starch-debranching enzyme isoforms were observed. High-performance size exclusion chromatography analysis shows that the chain-length profiles of amylopectin as well as β-limit dextrin were indistinguishable between wx and sbe1a wx, whereas significant differences for both were observed between ae wx and sbe1a ae wx, suggesting an effect of SBEIa on amylopectin biosynthesis that is observable only in the absence of SBEIIb. The amylopectin branch density and the average number of branches per cluster were both higher in endosperm starch from sbe1a ae wx than from ae wx. These results indicate possible functional interactions between SBE isoforms that may involve enzymatic inhibition. Both the cluster repeat distance and the distance between branch points on the short intracluster chains were similar for all genotypes however, suggesting a similar pattern of individual SBE isoforms in cluster initiation and the determination of branch point location.
机译：先前的研究表明，单个突变体sbe1a∷Mu（sbe1a）中的淀粉分支酶（SBE）Ia缺乏对胚乳淀粉结构没有影响，而众所周知ae突变体中SBEIIb的缺乏会减少淀粉的分支。淀粉。我们假设在玉米（Zea mays）胚乳中，SBEIIb的功能主要是SBEIa的功能，而在没有SBEIIb的情况下，SBEIa仅对支链淀粉的结构具有可观察的作用。为了验证这一假设，将突变的sbe1a插入W64A背景中的wx（缺少与颗粒结合的淀粉合酶GBSSI）或ae wx（缺少SBEIIb和GBSSI）的品系中。 Western blotting和酶谱分析均证实sbe1a wx和sbe1a ae wx中SBEIa缺乏，而ae wx和sbe1a ae wx中SBEIIb缺乏。使用酶谱分析，未观察到sbe1a基因对SBEIIa，淀粉合酶或淀粉脱支酶同工型的多效性作用。高性能尺寸排阻色谱分析表明，支链淀粉和β-极限糊精的链长分布在wx和sbe1a wx之间没有区别，而在ae wx和 sbe1a ae wx之间观察到两者的显着差异，表明SBEIa对支链淀粉生物合成的影响只有在不存在SBEIIb时才能观察到。 sbe1a ae wx 的胚乳淀粉中支链淀粉的分支密度和平均每簇的平均分支数目均高于 ae wx。。这些结果表明，SBE亚型之间可能存在功能相互作用。可能涉及酶促抑制。对于所有基因型，簇重复距离和短簇内链上分支点之间的距离都相似，但是，这表明在簇起始和分支点位置确定中单个SBE同工型的模式相似。

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