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首页> 美国卫生研究院文献>Molecular Biology and Evolution >Molecular Basis of the Waxy Endosperm Starch Phenotype in Broomcorn Millet (Panicum miliaceum L.)
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Molecular Basis of the Waxy Endosperm Starch Phenotype in Broomcorn Millet (Panicum miliaceum L.)

机译：room粟（Panicum miliaceum L.）的蜡状胚乳淀粉表型的分子基础

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Waxy varieties of the tetraploid cereal broomcorn millet (Panicum miliaceum L.) have endosperm starch granules lacking detectable amylose. This study investigated the basis of this phenotype using molecular and biochemical methods. Iodine staining of starch granules in 72 plants from 38 landrace accessions found 58 nonwaxy and 14 waxy phenotype plants. All waxy types were in plants from Chinese and Korean accessions, a distribution similar to that of the waxy phenotype in other cereals. Granule-bound starch synthase I (GBSSI) protein was present in the endosperm of both nonwaxy and waxy individuals, but waxy types had little or no granule-bound starch synthase activity compared with the wild types. Sequencing of the GBSSI (Waxy) gene showed that this gene is present in two different forms (L and S) in P. miliaceum, which probably represent homeologues derived from two distinct diploid ancestors. Protein products of both these forms are present in starch granules. We identified three polymorphisms in the exon sequence coding for mature GBSSI peptides. A 15-bp deletion has occurred in the S type GBSSI, resulting in the loss of five amino acids from glucosyl transferase domain 1 (GTD1). The second GBSSI type (L) shows two sequence polymorphisms. One is the insertion of an adenine residue that causes a reading frameshift, and the second causes a cysteine–tyrosine amino acid polymorphism. These mutations appear to have occurred in parallel from the ancestral allele, resulting in three GBSSI-L alleles in total. Five of the six possible genotype combinations of the S and L alleles were observed. The deletion in the GBSSI-S gene causes loss of protein activity, and there was 100% correspondence between this deletion and the waxy phenotype. The frameshift mutation in the L gene results in the loss of L-type protein from starch granules. The L isoform with the tyrosine residue is present in starch granules but is nonfunctional. This loss of function may result from the substitution of tyrosine for cysteine, although it could not be determined whether the cysteine isoform of L represents the functional type. This is the first characterization of mutations that occur in combination in a functionally polyploid species to give a fully waxy phenotype.
机译：四倍体谷物b帚小米（Panicum miliaceum L.）的蜡状品种的胚乳淀粉颗粒缺乏可检测的直链淀粉。本研究使用分子和生化方法研究了该表型的基础。从38个地方品种的72种植物中对淀粉颗粒进行碘染色，发现58种非蜡质和14种蜡质表型植物。所有蜡质类型都来自中国和韩国的植物，其分布与其他谷物的蜡质表型相似。非蜡质和蜡质个体的胚乳中均存在颗粒结合的淀粉合酶I（GBSSI）蛋白，但是蜡质类型的淀粉合酶活性与野生型相比几乎没有或没有。 GBSSI（Waxy）基因的测序表明，该基因以两种不同的形式（L和S）存在于粟酒裂殖酵母中，这很可能代表了源自两个不同二倍体祖先的同源物。这两种形式的蛋白质产物都存在于淀粉颗粒中。我们在编码成熟GBSSI肽的外显子序列中发现了三个多态性。 S型GBSSI中发生了15 bp的缺失，导致葡萄糖基转移酶结构域1（GTD1）丢失了五个氨基酸。第二种GBSSI类型（L）显示两个序列多态性。第一个是腺嘌呤残基的插入导致阅读移码，第二个引起半胱氨酸-酪氨酸氨基酸多态性。这些突变似乎与祖先等位基因平行发生，导致总共三个GBSSI-L等位基因。观察到S和L等位基因的六个可能的基因型组合中的五个。 GBSSI-S基因的缺失会导致蛋白质活性下降，并且该缺失与蜡状表型之间存在100％的对应关系。 L基因中的移码突变导致淀粉颗粒中L型蛋白的丢失。具有酪氨酸残基的L同工型存在于淀粉颗粒中，但是没有功能。尽管无法确定L的半胱氨酸同工型是否代表功能类型，但这种功能丧失可能是由酪氨酸替代半胱氨酸引起的。这是在功能多倍体物种中结合出现以产生完全蜡质表型的突变的第一个特征。

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