AGPs (Arabinogalactan Proteins)是一类糖基化程度最高的细胞壁蛋白，含有不到10%分子量的蛋白质主链，而多糖侧链占了分子量的90%以上，这意味着多糖侧链可能在AGP功能及其分子间相互作用上发挥重要作用，但关于AGPs多糖侧链生物合成的酶学却知之甚少，多糖侧链在AGPs功能发挥中的实际作用也未知。我们在前期工作中分离克隆了三个棉纤维发育相关的AGP特异的将第一个半乳糖转移到蛋白质主链羟脯氨酸残基上进而起始多糖侧链合成的半乳糖基转移酶 (AGP-GalTs)，本项目拟通过蛋白表达、酶活与酶反应产物分析，蛋白质相互作用分析研究AGP-GalTs在多糖侧链合成中的作用，利用overexpression和RNAi技术，结合拟南芥同源基因突变体的分析，揭示多糖侧链在AGP功能发挥中的贡献及AGP-GalTs在棉纤维发育中的生物学意义。

Arabinogalactan proteins(AGPs) are among the most highly glycosylated proteins in nature.Polysaccharide side chains account for 90% of their molecular weights which means glycans generally define the interactive molecular surface of AGPs and their function.However,precise roles of AGP glycosylation remain elusive and little is known about specific glycosyltransferases involved in the process.The cotton fiber represents an excellent model to study plant cell elongation and cell wall biogenesis.Based on our previous studies,three genes encoding galactosyltransferases which initiate synthesis of the polysaccharide side chains of AGPs（AGP-GalTs）were isolated.All the three genes are fiber developmental stage regulated.In this study,to elucidate the roles of AGP-GalTs which play in the synthesis of polysaccharide side chains,the AGP-GalT genes will be expressed in Pichia and tobacco BY-2 cells, the produced GalTs will be tested for AGP-GalT activity with the in vitro enzyme assay.Reaction products from these assays will be biochemically characterized.In order to understand the contribution of polysaccharide side chains to AGPs function and the roles of AGP-GalTs which play during the fiber development,genetic methods of overexpression and RNAi will be employed and T-DNA mutants of homologous genes in Arabidopsis will also be characterized.