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Plant Physiology：OsMADS57作用于水稻根中氮向地上组织的转运

已有 2617 次阅读 2019-3-19 15:34 |个人分类:每日摘要|系统分类:论文交流

A Transcription Factor, OsMADS57, Regulates Long-distance Nitrate Transport and Root Elongation

First author: Shuangjie Huang; Affiliations: Xinyang Agriculture and Forestry University (信阳农林学院): Xinyang, China

Corresponding author: Yali Zhang

Root nitrate uptake adjusts to the plant's nitrogen demand for growth. Here we report that OsMADS57, a MADS-box transcription factor, modulates nitrate translocation from rice (Oryza sativa) roots to shoots under low-nitrate conditions. OsMADS57 is abundantly expressed in xylem parenchyma cells (薄壁细胞) of root stele (中柱) and is induced by nitrate. Compared with wild-type rice plants supplied with 0.2 mM nitrate, osmads57 mutants had 31% less xylem loading of nitrate, while overexpression lines had two-fold higher levels. Shoot-root 15N content ratios were 40% lower in the mutants and 76% higher in the overexpression lines. Rapid NO3- root influx experiments showed that mutation of OsMADS57 did not affect root nitrate uptake. RT-qPCR analysis of OsNRT2 nitrate transporter genes showed that after 5 min in 0.2 mM nitrate, only OsNRT2.3a (a vascular-specific high-affinity nitrate transporter) had reduced (by two-thirds) expression levels. At 60 min of nitrate treatment, lower expression levels were also observed for three additional NRT2 genes (OsNRT2.1/2.2/2.4). Conversely, in the overexpression lines, four NRT2 genes had much higher expression profiles at all time points tested. As previously reported, OsNRT2.3a functions in nitrate translocation, indicating the possible interaction between OsMADS57 and OsNRT2.3a. Yeast one-hybrid and transient expression assays demonstrated that OsMADS57 binds to the CArG motif [CATTTTATAG] within the OsNRT2.3a promoter. Moreover, seminal root elongation was inhibited in osmads57 mutants, which may be associated with higher auxin levels in and auxin polar transport to root tips of mutant plants. Taken together, these results suggest that OsMADS57 has a role in regulating nitrate translocation from root to shoot via OsNRT2.3a.

植物的根从土壤吸收氮来供应植物生长所需。本文报道了水稻中的一个名为OsMADS57的MADS-box转录因子能够在低氮条件下调节氮从根向地上组织的迁移。OsMADS57主要在根中柱的木质部薄壁细胞中表达，并且其表达受到氮的诱导。在0.2 mM的氮浓度下，osmads57突变体木质部运输氮的量要比野生型少31%，而过表达株系则高出两倍左右。地上与地下15N含量比率在突变体中下降40%，而在过表达株系中则上升76%。根部NO3-快速流入试验显示OsMADS57的突变并不影响水稻对氮的吸收。对于OsNRT2基因的RT-qPCR试验显示在0.2 mM的氮处理5分钟后，仅仅只有维管组织特异性高亲和力氮转运体OsNRT2.3a的表达水平下降了2-3倍。在氮处理60分钟后，另外三个NRT2基因OsNRT2.1/2.2/2.4也表现出了表达水平下降。相反，在过表达株系中，这四个NRT2在所有检测的时间点均具有较高的表达量。正如先前所报道的一样，OsNRT2.3a作用于氮的转运，说明OsMADS57和OsNRT2.3a之间可能存在潜在的相互作用。酵母单杂和瞬间表达试验显示OsMADS57能够结合到OsNRT2.3a启动子区的CArG基序。此外，osmads57突变体种子根的伸长受到了抑制，这可能与较高的生长素水平以及生长素极性运输倒根尖组织有关。综上，本文的研究结果揭示了OsMADS57通过OsNRT2.3a作用于植物中的氮从根运输到地上组织。