Gao M, Chibbar R N
National Research Council of Canada, Plant Biotechnology Institute, Saskatoon, SK, Canada.
Genome. 2000 Oct;43(5):768-75.
We characterized three near-full-length putative homoeologous cDNA (Ss2a-1, Ss2a-2, and Ss2a-3) in wheat endosperm most similar to the maize zSSIIa. Polypeptide sequences deduced from three Ss2a cDNA clones share a 95% overall sequence similarity, and may thus have similar biochemical properties and may make identical contributions to starch biosynthesis in wheat endosperm. The accumulation of RNA transcripts corresponding to three Ss2a genes in developing endosperm varies among three cultivars studied, but usually peaks in young endosperm at about 10 days post anthesis (DPA). The polyclonal antibody for the SSIIa-1 recombinant protein strongly reacted to three previously identified granule-bound starch synthases of 100 to 115 kDa. The polyclonal antibody for the granule-bound starch synthases strongly reacted to the SSIIa-1 recombinant protein. Sequences of the N-terminal and an internal peptide of these three granule-bound starch synthases match well with those of three predicted mature SSIIa polypeptides. These granule-bound starch synthases may therefore be SSIIa polypeptides. The antibodies also recognized a group of three polypeptides with the same gel mobility as the three granule-bound starch synthases, a polypeptide of 90 kDa, and a group of three polypeptides of about 80 to 82 kDa. Thus, the wheat SSIIa may exist in several functional forms in the stroma of amyloplasts.
我们鉴定了小麦胚乳中三个与玉米zSSIIa最相似的近全长推定同源cDNA（Ss2a-1、Ss2a-2和Ss2a-3）。从三个Ss2a cDNA克隆推导的多肽序列总体序列相似性为95%，因此可能具有相似的生化特性，并可能对小麦胚乳中的淀粉生物合成做出相同贡献。在发育中的胚乳中，对应于三个Ss2a基因的RNA转录本的积累在所研究的三个品种中有所不同，但通常在开花后约10天（DPA）的幼胚乳中达到峰值。针对SSIIa-1重组蛋白的多克隆抗体与先前鉴定的三种100至115 kDa的颗粒结合淀粉合酶强烈反应。针对颗粒结合淀粉合酶的多克隆抗体与SSIIa-1重组蛋白强烈反应。这三种颗粒结合淀粉合酶的N端和内部肽段序列与三种预测的成熟SSIIa多肽的序列匹配良好。因此，这些颗粒结合淀粉合酶可能是SSIIa多肽。这些抗体还识别出一组与三种颗粒结合淀粉合酶具有相同凝胶迁移率的三种多肽、一种90 kDa的多肽以及一组约80至82 kDa的三种多肽。因此，小麦SSIIa可能以几种功能形式存在于造粉体基质中。
