title: Comparative characterization of GmSPX members reveals that GmSPX3 is involved in phosphate homeostasis in soybean.
abstract: OBJECTIVE
  Proteins containing the SPX (SYG1/Pho81/XPR1) domain are vital components in the phosphorus (P) signalling pathway, and regulate phosphate (Pi) homeostasis in plants. However, the characteristics and functions of GmSPX members in soybean (Glycine max) remain largely unknown.
  
  
  METHODS
  BLAST searching revealed nine GmSPX members in the soybean genome. Subsequently, expression patterns of GmSPX members were investigated in various tissues of soybean grown in nutrient solution or sand culture through quantitative real-time PCR (qPCR) analysis. Sub-cellular localization of GmSPX was examined via transient expression of 35S:GmSPX-GFP in epidermal cells of onion (Allium cepa). Finally, soybean transgenic composite plants were generated to study GmSPX3 functions.
  
  
  RESULTS
  Nine GmSPX members were identified, which were classified into three groups based on phylogenetic analysis. Diverse responses of GmSPX members to deficiencies of nutrients (nitrogen, phosphorus, potassium and iron) or inoculation of arbuscular mycorrhizal fungi and rhizobia were observed in soybean. In addition, variations of sub-cellular localization of GmSPX members were found. Among them, GmSPX3, GmSPX7 and GmSPX8 were localized in the nuclei, and the other GmSPX members were confined to the nuclei and cytoplasm. The nuclear-localized and Pi starvation responsive-gene, GmSPX3, was functionally analysed in soybean transgenic composite plants. Overexpression of GmSPX3 led to increased P concentrations in both shoots and roots in the high-P treatment, and increased transcription of seven Pi starvation-responsive genes in soybean hairy roots.
  
  
  CONCLUSIONS
  Taken together, the results suggest that GmSPX3 is a positive regulator in the P signalling network, and controls Pi homeostasis in soybean.
authors: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, PR China.
authors: Zhufang
authors: Z
authors: Yao
authors: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, PR China jtian@scau.edu.cn.
authors: Jiang
authors: J
authors: Tian
authors: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, PR China.
authors: Hong
authors: H
authors: Liao
mesh_terms: D018506:Gene Expression Regulation, Plant; D006706:Homeostasis; D008969:Molecular Sequence Data; D010710:Phosphates / Q000378:metabolism*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism / Q000502:physiology; D060888:Real-Time Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013025:Glycine max / Q000378:metabolism / Q000502:physiology*
chemical_list: D010710:Phosphates; D010940:Plant Proteins
keywords: Expression pattern; Glycine max; GmSPX members; Pi homeostasis; SPX domain; phosphate starvation; phosporus signalling; soybean