氮、磷都是植物生长必需的大量营养元素，提高作物的氮、磷效率，达到氮/磷协同高效是农业生产可持续发展的重要途径。已有的报道及我们前期工作均表明，豆科作物共生固氮的关键因子－根瘤对低磷胁迫具有特异的适应机制。其中，细胞壁扩张蛋白可能参与了协同调控根与根瘤对低磷胁迫的适应性响应。本项目拟利用我们前期克隆的，在大豆根系及根瘤生长不同时期受低磷诱导表达的细胞壁扩张蛋白GmEXPB2 和GmEXPB6，通过生理功能分析、分子生物学技术和转基因手段，综合解析GmEXPB2和GmEXPB6在磷调控大豆根、根瘤生长中的具体功能，探讨根与根瘤协同适应低磷胁迫的机制，以期为作物氮/磷协同高效遗传改良提供候选基因和创制氮/磷协同高效的大豆新材料。

Both nitrogen (N) and phosphorus (P) are essential elements for plant growth. It is an important strategy for sustainable agriculture to improve crop efficiency in both N and P, and thereby achieve coordinative high efficiency of N and P. Previous reports and our researches indicated that nodule, a key factor for biological nitrogen fixation, had evolved some special adaptive mechanisms to low P stress. Among them, expansins may be involved in coordinative controls of adaptive responses of roots and nodules to low P stress. In the present study, GmEXPB2 and GmEXPB6, the two expansin genes which had been previously cloned and proved to be induced by low P at different growth stages of roots and nodules in soybean by our lab, will be used. Through physiological function analysis, molecular techniques and plant gene transformation methods, the detailed functions of GmEXPB2 and GmEXPB6 in growth of soybean roots and nodules as regulated by P will be comprehensively analyzed , and the underlying mechanisms of coordinative adaptations of roots and nodules to low P stress will be explored. Our research might provide candidate genes for genetic improvements of crops with coordinative high efficiency of N and P, and generate some new soybean materials with coordinative high efficiency of N and P.