Abstract：
Phosphorus (P) deficiency adversely affects nodule development as reflected by reduced nodule fresh weight in legume plants. Though mechanisms underlying nodule adaptation to P deficiency have been studied extensively, it remains largely unknown which regulator mediates nodule adaptation to P deficiency. In this study, GUS staining and quantitative reverse transcription-PCR analysis reveal that the SPX member GmSPX5 is preferentially expressed in soybean (Glycine max) nodules. Overexpression of GmSPX5 enhanced soybean nodule development particularly under phosphate (Pi) sufficient conditions. However, the Pi concentration was not affected in soybean tissues (i.e., leaves, roots, and nodules) of GmSPX5 overexpression or suppression lines, which distinguished it from other well-known SPX members functioning in control of Pi homeostasis in plants. Furthermore, GmSPX5 was observed to interact with the transcription factor GmNF-YC4 in vivo and in vitro. Overexpression of either GmSPX5 or GmNF-YC4 significantly upregulated the expression levels of five asparagine synthetase-related genes (i.e., GmASL2-6) in soybean nodules. Meanwhile, yeast one-hybrid and luciferase activity assays strongly suggested that interactions of GmSPX5 and GmNF-YC4 activate GmASL6 expression through enhancing GmNF-YC4 binding of the GmASL6 promoter. These results not only demonstrate the GmSPX5-GmNF-YC4-GmASL6 regulatory pathway mediating soybean nodule development, but also considerably improve our understanding of SPX functions in legume crops.
摘要：
磷（P）缺乏会对根瘤发育产生不利影响，这反映在豆科植物根瘤鲜重的减少上。尽管根瘤对P缺乏的适应机制已经得到了广泛的研究，目前尚不清楚哪个调节因子介导结节对P缺乏的适应。在这项研究中,GUS染色和定量逆转录PCR分析揭示SPX成员GmSPX5优先在大豆(Glycinemax)结节中表达。特别是在磷酸盐（Pi）充足的条件下，GmSPX5的过表达增强了大豆根瘤的发育。然而,大豆组织中的Pi浓度不受影响(即，叶子,根,和结节）的GmSPX5过表达或抑制系，将其与在植物中控制Pi稳态中起作用的其他众所周知的SPX成员区分开。此外，观察到GmSPX5在体内和体外与转录因子GmNF-YC4相互作用。GmSPX5或GmNF-YC4的过表达显着上调了五个天冬酰胺合成酶相关基因的表达水平（即，大豆结节中的GmASL2-6)。同时,酵母单杂交和荧光素酶活性测定强烈表明，GmSPX5和GmNF-YC4的相互作用通过增强GmNF-YC4与GmASL6启动子的结合来激活GmASL6的表达。这些结果不仅证明了GmSPX5-GmNF-YC4-GmASL6调节途径介导大豆根瘤发育，而且大大提高了我们对豆科作物中SPX功能的理解。
