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Abstract：
Though root architecture modifications may be critically important for improving phosphorus (P) efficiency in crops, the regulatory mechanisms triggering these changes remain unclear. In this study, we demonstrate that genotypic variation in GmEXPB2 expression is strongly correlated with root elongation and P acquisition efficiency, and enhancing its transcription significantly improves soybean yield in the field. Promoter deletion analysis was performed using 5\' truncation fragments (P1-P6) of GmEXPB2 fused with the GUS gene in soybean transgenic hairy roots, which revealed that the P1 segment containing three E-box elements significantly enhances induction of gene expression in response to phosphate (Pi) starvation. Further experimentation demonstrated that GmPTF1, a basic-helix-loop-helix transcription factor, is the regulatory factor responsible for the induction of GmEXPB2 expression in response to Pi starvation. In short, Pi starvation induced expression of GmPTF1, with the GmPTF1 product directly binding to the E-box motif in the P1 region of the GmEXPB2 promoter. Plus, both GmPTF1 and GmEXPB2 highly expressed in lateral roots, and were significantly enhanced by P deficiency. Further work with soybean stable transgenic plants through RNA sequencing analysis showed that altering GmPTF1 expression significantly impacted the transcription of a series of cell wall genes, including GmEXPB2, and thereby affected root growth, biomass and P uptake. Taken together, this work identifies a novel regulatory factor, GmPTF1, involved in changing soybean root architecture partially through regulation of the expression of GmEXPB2 by binding the E-box motif in its promoter region.
摘要：
尽管根系结构的改变对于提高作物中的磷（P）效率可能至关重要，触发这些变化的监管机制仍不清楚。在这项研究中,我们证明GmEXPB2表达的基因型变异与根伸长和P获得效率密切相关，增强其转录水平显著提高了大田大豆产量。使用与大豆转基因毛状根中GUS基因融合的GmEXPB2的5个截短片段（P1-P6）进行启动子缺失分析，这表明包含三个E-box元件的P1片段显着增强了响应于磷酸盐（Pi）饥饿的基因表达的诱导。进一步的实验表明，GmPTF1是一种碱性螺旋-环-螺旋转录因子，是负责响应Pi饥饿诱导GmEXPB2表达的调节因子。总之,Pi饥饿诱导GmPTF1的表达，GmPTF1产物直接与GmEXPB2启动子P1区的E-box基序结合。另外，GmPTF1和GmEXPB2在侧根中高表达，并因P缺乏而显着增强。通过RNA测序分析，对大豆稳定转基因植物的进一步研究表明，改变GmPTF1表达显著影响一系列细胞壁基因的转录，包括GmEXPB2，从而影响根系生长，生物量和磷吸收。一起来看,这项工作确定了一个新的调节因子，GmPTF1通过在其启动子区域结合E盒基序来调节GmEXPB2的表达，部分参与改变大豆根结构。
