細(xì)胞壁是由纖維素,、半纖維素和果膠構(gòu)成的復(fù)雜多糖網(wǎng)絡(luò)結(jié)構(gòu),，也是植物膨壓驅(qū)動(dòng)細(xì)胞生長(zhǎng)的物質(zhì)基礎(chǔ),。水稻細(xì)胞壁研究對(duì)于抗倒伏和水稻植株形態(tài)等農(nóng)藝性狀的改良具有重要意義,。植物細(xì)胞壁多糖除纖維素在質(zhì)膜上合成外,，其他多糖主要在高爾基體內(nèi)合成,。而所需底物,、各種核苷糖分子（nucleotide sugar）卻主要在細(xì)胞質(zhì)中合成，需要通過核苷糖轉(zhuǎn)運(yùn)子跨膜運(yùn)輸?shù)礁郀柣w內(nèi),，參與多糖合成,。研究證明底物合成的缺陷可以影響細(xì)胞壁的合成，因此人們推測(cè)核苷糖轉(zhuǎn)運(yùn)子對(duì)細(xì)胞壁合成有重要影響,，然而這一假設(shè)由于缺乏遺傳學(xué)證據(jù),，一直存在很大的爭(zhēng)議。
我們通過鑒定一個(gè)新的水稻脆稈突變體bc14發(fā)現(xiàn),，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(zhuǎn)運(yùn)子,，參與細(xì)胞壁多糖合成。對(duì)bc14突變體的詳細(xì)表型分析發(fā)現(xiàn),，基因突變引起次生壁結(jié)構(gòu)異常和纖維素含量下降,，導(dǎo)致機(jī)械強(qiáng)度顯著下降和生長(zhǎng)發(fā)育缺陷?；蚩寺『突パa(bǔ)實(shí)驗(yàn)發(fā)現(xiàn)突變表型是由核苷酸糖轉(zhuǎn)運(yùn)子Oryza sativa Nucleotide Sugar Transporter1 ()基因的錯(cuò)義突變引起,。水稻原生質(zhì)體表達(dá)BC14/OsNST1融合熒光蛋白載體發(fā)現(xiàn)該蛋白定位于高爾基體中。體外酶活實(shí)驗(yàn)證明該轉(zhuǎn)運(yùn)子具有尿苷二磷酸-葡萄糖的轉(zhuǎn)運(yùn)活性,。細(xì)胞壁成分的詳細(xì)分析證實(shí)突變體基質(zhì)多糖中葡萄糖含量明顯下降,。
本研究證實(shí)了高爾基體定位的核苷糖轉(zhuǎn)運(yùn)子在細(xì)胞壁多糖合成中的重要作用，為解析細(xì)胞壁生物合成的生化和生物學(xué)機(jī)制提供了關(guān)鍵的證據(jù),，解決了該領(lǐng)域中一個(gè)長(zhǎng)期懸而未決的重要問題,。這項(xiàng)工作已于2011年3月7日在國(guó)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(guó)農(nóng)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(guó)家轉(zhuǎn)基因?qū)ｍ?xiàng)和中科院知識(shí)創(chuàng)新方向性項(xiàng)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.
