Barley sex6 mutants lack starch synthase IIa activity and contain a starch with novel properties
Barley sex6 mutants lack starch synthase IIa activity and contain a starch with novel properties
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DOI：
10.1046/j.1365-313x.2003.01712.x
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发表时间：
2003-04-01
期刊：
影响因子：
7.2
通讯作者：
Li, ZY
中科院分区：
文献类型：
--
作者：
Morell, MK;Kosar-Hashemi, B;Li, ZY
分析大麦瘪粒突变体已经鉴定出具有新的高直链淀粉表型的品系。致病突变位于染色体7H上的sex6位点，表明淀粉合成酶IIa（ssIIa）基因作为突变改变的候选基因。与这一假设一致，没有发现淀粉粒或胚乳可溶性部分中SSIIa蛋白表达的证据。来自三个独立sex 6系的淀粉合成酶IIa基因ssIIa的序列显示存在一个终止密码子，阻止每个系中ssIIa转录本的翻译。在ssIIa基因中存在终止密码子的淀粉表型的完美分离，为ssIIa基因中的病变是sex6表型的致病突变提供了有力的证据。大麦中SSIIa活性的丧失导致新的和信息丰富的表型。首先，支链淀粉合成减少到野生型水平的20%以下表明SSIIa占大麦中支链淀粉聚合物伸长活性的大部分。其次，与支化酶下调导致的高直链淀粉相反，sex6淀粉具有缩短的支链淀粉链长分布和降低的糊化温度。第三，突变导致对淀粉生物合成途径的其他酶的多效性效应，废除SSI、分支酶IIa和分支酶IIb与sex6突变体的淀粉颗粒的结合，同时不显著改变它们在可溶性级分中的表达水平。
Analysis of barley shrunken grain mutants has identified lines with a novel high amylose starch phenotype. The causal mutation is located at the sex6 locus on chromosome 7H, suggesting the starch synthase IIa (ssIIa ) gene as a candidate gene altered by the mutation. Consistent with this hypothesis, no evidence of SSIIa protein expression in either the starch granule or soluble fractions of the endosperm was found. Sequences of the starch synthase IIa gene, ssIIa , from three independent sex6 lines showed the presence of a stop codon preventing translation of the ssIIa transcript in each line. Perfect segregation of the starch phenotype with the presence of stop codons in the ssIIa gene was obtained, providing strong evidence for the lesion in the ssIIa gene being the causal mutation for the sex6 phenotype. The loss of SSIIa activity in barley leads to novel and informative phenotypes. First, a decrease in amylopectin synthesis to less than 20% of the wild-type levels indicates that SSIIa accounts for the majority of the amylopectin polymer elongation activity in barley. Secondly, in contrast to high amylose starches resulting from branching enzyme downregulation, the sex6 starches have a shortened amylopectin chain length distribution and a reduced gelatinisation temperature. Thirdly, the mutation leads to pleiotropic effects on other enzymes of the starch biosynthesis pathway, abolishing the binding of SSI, branching enzyme IIa and branching enzyme IIb to the starch granules of sex6 mutants, while not significantly altering their expression levels in the soluble fraction.