細胞壁是由纖維素,、半纖維素和果膠構成的復雜多糖網絡結構,，也是植物膨壓驅動細胞生長的物質基礎,。水稻細胞壁研究對于抗倒伏和水稻植株形態(tài)等農藝性狀的改良具有重要意義,。植物細胞壁多糖除纖維素在質膜上合成外,，其他多糖主要在高爾基體內合成,。而所需底物,、各種核苷糖分子（nucleotide sugar）卻主要在細胞質中合成，需要通過核苷糖轉運子跨膜運輸到高爾基體內,，參與多糖合成,。研究證明底物合成的缺陷可以影響細胞壁的合成，因此人們推測核苷糖轉運子對細胞壁合成有重要影響,，然而這一假設由于缺乏遺傳學證據,，一直存在很大的爭議。
我們通過鑒定一個新的水稻脆稈突變體bc14發(fā)現,，其野生型基因編碼高爾基體定位的尿苷二磷酸-葡萄糖（UDP-Glucose）轉運子,，參與細胞壁多糖合成,。對bc14突變體的詳細表型分析發(fā)現，基因突變引起次生壁結構異常和纖維素含量下降,，導致機械強度顯著下降和生長發(fā)育缺陷,。基因克隆和互補實驗發(fā)現突變表型是由核苷酸糖轉運子Oryza sativa Nucleotide Sugar Transporter1 ()基因的錯義突變引起,。水稻原生質體表達BC14/OsNST1融合熒光蛋白載體發(fā)現該蛋白定位于高爾基體中,。體外酶活實驗證明該轉運子具有尿苷二磷酸-葡萄糖的轉運活性。細胞壁成分的詳細分析證實突變體基質多糖中葡萄糖含量明顯下降,。
本研究證實了高爾基體定位的核苷糖轉運子在細胞壁多糖合成中的重要作用,，為解析細胞壁生物合成的生化和生物學機制提供了關鍵的證據，解決了該領域中一個長期懸而未決的重要問題,。這項工作已于2011年3月7日在國際雜志PNAS上在線發(fā)表（DOI:/10.1073/pnas.1016144108）,。周奕華課題組張保才、劉香玲和中國農科院水稻所錢前研究員為該論文的共同第一作者,。該研究得到了國家轉基因專項和中科院知識創(chuàng)新方向性項目的資助,。（生物谷Bioon.com）
生物谷推薦原文出處：
PNAS DOI:10.1073/pnas.1016144108
Golgi nucleotide sugar transporter modulates cell wall biosynthesis and plant growth in rice
Baocai Zhang,Xiangling Liu,Qian Qian,Lifeng Liu,Guojun Dong,Guangyan Xiong,Dali Zeng,and Yihua Zhou
Abstract
Golgi-localized nucleotide sugar transporters (NSTs) are considered essential for the biosynthesis of wall polysaccharides and glycoproteins based on their characteristic transport of a large number of nucleotide sugars to the Golgi lumen. The lack of NST mutants in plants has prevented evaluation of this hypothesis in plants. A previously undescribed Golgi NST mutant, brittle culm14 (bc14), displays reduced mechanical strength caused by decreased cellulose content and altered wall structure, and exhibits abnormalities in plant development. Map-based cloning revealed that all of the observed mutant phenotypes result from a missense mutation in a putative NST gene, Oryza sativa Nucleotide Sugar Transporter1 (OsNST1). OsNST1 was identified as a Golgi-localized transporter by analysis of a fluorescence-tagged OsNST1 expressed in rice protoplast cells and demonstration of UDP-glucose transport activity via uptake assays in yeast. Compositional sugar analyses in total and fractionated wall residues of wild-type and bc14 culms showed a deficiency in the synthesis of glucoconjugated polysaccharides in bc14, indicating that OsNST1 supplies the glucosyl substrate for the formation of matrix polysaccharides, and thereby modulates cellulose biosynthesis. OsNST1 is ubiquitously expressed, with high expression in mechanical tissues. The inferior mechanical strength and abnormal development of bc14 plants suggest that OsNST1 has pleiotropic effects on cell wall biosynthesis and plant growth. Identification of OsNST1 has improved our understanding of how cell wall polysaccharide synthesis is regulated by Golgi NSTs in plants.
