Li Z, Chu X, Mouille G, Yan L, Kosar-Hashemi B, Hey S, Napier J, Shewry P, Clarke B, Appels R, Morell M K, Rahman S
Commonwealth Scientific and Industrial Research Organization, Plant Industry, G.P.O. Box 1600, Canberra, Australian Capital Territory 2601, Australia.
Plant Physiol. 1999 Aug;120(4):1147-56. doi: 10.1104/pp.120.4.1147.
The starch granules of hexaploid wheat (Triticum aestivum) contain a group of three proteins known as SGP-1 (starch granule protein-1) proteins, which have apparent molecular masses of 100, 108, and 115 kD. The nature and role of these proteins has not been defined previously. We demonstrate that these polypeptides are starch synthases that are present in both the starch granule and the soluble fraction at the early stages of wheat endosperm development, but that are exclusively granule bound at mid and late endosperm development. A partial cDNA clone encoding a fragment of the 100-kD protein was obtained by screening a wheat endosperm cDNA expression library using monoclonal antibodies. Three classes of cDNA were subsequently isolated from a wheat endosperm cDNA library by nucleic acid hybridization and were shown to encode the 100-, 108-, and 115-kD proteins. The cDNA sequences are highly homologous to class II starch synthases and have the highest homology with the maize SSIIa (starch synthase IIa) gene. mRNA for the SGP-1 proteins was detected in the leaf, pre-anthesis florets, and endosperm of wheat and is highly expressed in the leaf and in the grain during the early to mid stages of development. We discuss the roles of the SGP-1 proteins in starch biosynthesis in wheat.
六倍体小麦（普通小麦）的淀粉颗粒含有一组三种蛋白质，称为SGP-1（淀粉颗粒蛋白-1）蛋白，其表观分子量分别为100、108和115 kD。这些蛋白质的性质和作用此前尚未明确。我们证明，这些多肽是淀粉合酶，在小麦胚乳发育早期存在于淀粉颗粒和可溶性部分中，但在胚乳发育中期和后期仅与颗粒结合。通过使用单克隆抗体筛选小麦胚乳cDNA表达文库，获得了编码100-kD蛋白片段的部分cDNA克隆。随后通过核酸杂交从小麦胚乳cDNA文库中分离出三类cDNA，它们被证明编码100-、108-和115-kD蛋白。这些cDNA序列与II类淀粉合酶高度同源，与玉米SSIIa（淀粉合酶IIa）基因的同源性最高。在小麦的叶片、花前小花和胚乳中检测到了SGP-1蛋白的mRNA，并且在发育早期至中期在叶片和籽粒中高度表达。我们讨论了SGP-1蛋白在小麦淀粉生物合成中的作用。
