Glyco-chain Functions Laboratory, RIKEN-FRS, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Phytochemistry. 2009 Dec;70(17-18):1973-81. doi: 10.1016/j.phytochem.2009.09.017. Epub 2009 Oct 12.
It is commonly accepted that sialic acids do not exist in plants. However, putative gene homologs of animal sialyltransferases and CMP-sialic acid transporters have been detected in the genomes of some plants. To elucidate the physiological functions of these genes, we cloned 2 cDNAs from Oryza sativa (Japanese rice), each of which encodes a CMP-sialic acid transporter-like protein designated as OsCSTLP1 and OsCSTLP2. To examine the CMP-sialic acid transporter activity of OsCSTLP1 and OsCSTLP2, we introduced their expression vectors into CMP-sialic acid transporter activity-deficient Lec2 cells. Transfection with OsCSTLP1 resulted in recovery of the deficit phenotype of Lec2 cells, but transfection with OsCSTLP2 did not. We also performed an in vitro nucleotide sugar transport assay using a yeast expression system. Among the nucleotide sugars examined, the OsCSTLP1-containing yeast microsomal membrane vesicles specifically incorporated CMP-sialic acid, indicating that OsCSTLP1 has CMP-sialic acid transporter activity. On the other hand, OsCSTLP2 did not exhibit any nucleotide sugar transporter activity. T-DNA insertion lines of Arabidopsis thaliana targeting the homologs of the OsCSTLP1 and OsCSTLP2 genes exhibited a lethal phenotype, suggesting that these proteins play important roles in plant development and may transport important nucleotide sugars such as CMP-Kdo in physiological conditions.
人们普遍认为唾液酸不存在于植物中。然而，一些植物的基因组中已经检测到了动物唾液酸转移酶和 CMP-唾液酸转运蛋白的假定基因同源物。为了阐明这些基因的生理功能，我们从水稻（Oryza sativa）中克隆了 2 个 cDNA，每个 cDNA 编码一种 CMP-唾液酸转运蛋白样蛋白，分别命名为 OsCSTLP1 和 OsCSTLP2。为了检测 OsCSTLP1 和 OsCSTLP2 的 CMP-唾液酸转运蛋白活性，我们将它们的表达载体导入 CMP-唾液酸转运蛋白活性缺陷型 Lec2 细胞中。转染 OsCSTLP1 导致 Lec2 细胞缺陷表型得到恢复，但转染 OsCSTLP2 则没有。我们还使用酵母表达系统进行了体外核苷酸糖转运测定。在检测的核苷酸糖中，含有 OsCSTLP1 的酵母微粒体膜囊泡特异性地摄取 CMP-唾液酸，表明 OsCSTLP1 具有 CMP-唾液酸转运蛋白活性。另一方面，OsCSTLP2 没有表现出任何核苷酸糖转运蛋白活性。拟南芥（Arabidopsis thaliana）的 T-DNA 插入系靶向 OsCSTLP1 和 OsCSTLP2 基因的同源物表现出致死表型，表明这些蛋白在植物发育中发挥重要作用，并可能在生理条件下转运重要的核苷酸糖，如 CMP-Kdo。
