Wang Yongqin, Xu Honglin, Wei Xiaoli, Chai Chenglin, Xiao Yuguo, Zhang Yu, Chen Bin, Xiao Guifang, Ouwerkerk Pieter B F, Wang Mei, Zhu Zhen
State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Beijing 100101, China.
Plant Mol Biol. 2007 Nov;65(4):439-51. doi: 10.1007/s11103-007-9228-x. Epub 2007 Sep 12.
Monosaccharide transporters mediate the membrane transport of a variable range of monosaccharides, which plays a crucial role in sugar distribution throughout the plant. To investigate the significance of monosaccharide transporters for rice (Oryza sativa L.) seed development, cDNA of a new putative monosaccharide transporter gene OsMST4 was isolated. The deduced OsMST4 protein shows typical features of monosaccharide transporters, and shares high homology with other plant homologues. Heterologous expression in yeast (Saccharomyces cerevisiae) showed that OsMST4 is a functional monosaccharide transporter capable of transporting glucose, fructose, mannose and galactose. Transcriptional analysis revealed that OsMST4 is expressed in all tested organs/tissues. In developing caryopses, its expression is high at the early and middle grain filling stages, and declines gradually to low levels after that. Further analysis revealed that it is expressed in both the maternal tissue and the filial tissue, with its highest expression in embryo. Cellular location in young caryopses through RNA in situ hybridization showed that OsMST4 mRNA mainly accumulates in the vascular parenchyma of the chalazal vein, cross-cells, nucellar tissue and endosperm. The expression pattern of OsMST4 was further confirmed by histochemical analysis of the OsMST4-promoter-beta-glucuronidase (GUS) transgenic rice plants. These data indicate that OsMST4 is actively involved in monosaccharides supply for seed development during the course of grain filling. In addition, the cell type-specific expression patterns of OsMST4 in other sink and source tissues were also investigated, and its corresponding physiological roles were discussed.
单糖转运蛋白介导多种单糖的膜转运，这在植物体内的糖分分配中起着关键作用。为了研究单糖转运蛋白对水稻种子发育的重要性，我们分离了一个新的假定单糖转运蛋白基因OsMST4的cDNA。推导的OsMST4蛋白具有单糖转运蛋白的典型特征，并且与其他植物同源物具有高度同源性。在酵母（酿酒酵母）中的异源表达表明，OsMST4是一种功能性单糖转运蛋白，能够转运葡萄糖、果糖、甘露糖和半乳糖。转录分析表明，OsMST4在所有测试的器官/组织中均有表达。在发育中的颖果中，其表达在灌浆早期和中期较高，之后逐渐下降至低水平。进一步分析表明，它在母体组织和子代组织中均有表达，在胚中表达最高。通过RNA原位杂交在幼嫩颖果中的细胞定位显示，OsMST4 mRNA主要积累在合点端维管束薄壁细胞、横向细胞、珠心组织和胚乳中。通过对OsMST4启动子-β-葡萄糖醛酸酶（GUS）转基因水稻植株的组织化学分析，进一步证实了OsMST4的表达模式。这些数据表明，OsMST4在灌浆过程中积极参与种子发育的单糖供应。此外，还研究了OsMST4在其他库源组织中的细胞类型特异性表达模式，并讨论了其相应的生理作用。
