Department of Molecular and Cellular Biology, University of Guelph, Guelph, Canada.
PLoS Genet. 2011 Mar;7(3):e1002021. doi: 10.1371/journal.pgen.1002021. Epub 2011 Mar 24.
Plants need abundant nitrogen and phosphorus for higher yield. Improving plant genetics for higher nitrogen and phosphorus use efficiency would save potentially billions of dollars annually on fertilizers and reduce global environmental pollution. This will require knowledge of molecular regulators for maintaining homeostasis of these nutrients in plants. Previously, we reported that the NITROGEN LIMITATION ADAPTATION (NLA) gene is involved in adaptive responses to low-nitrogen conditions in Arabidopsis, where nla mutant plants display abrupt early senescence. To understand the molecular mechanisms underlying NLA function, two suppressors of the nla mutation were isolated that recover the nla mutant phenotype to wild type. Map-based cloning identified these suppressors as the phosphate (Pi) transport-related genes PHF1 and PHT1.1. In addition, NLA expression is shown to be regulated by the low-Pi induced microRNA miR827. Pi analysis revealed that the early senescence in nla mutant plants was due to Pi toxicity. These plants accumulated over five times the normal Pi content in shoots specifically under low nitrate and high Pi but not under high nitrate conditions. Also the Pi overaccumulator pho2 mutant shows Pi toxicity in a nitrate-dependent manner similar to the nla mutant. Further, the nitrate and Pi levels are shown to have an antagonistic crosstalk as displayed by their differential effects on flowering time. The results demonstrate that NLA and miR827 have pivotal roles in regulating Pi homeostasis in plants in a nitrate-dependent fashion.
植物需要丰富的氮和磷才能获得更高的产量。提高植物对氮和磷的利用效率的遗传特性将使每年在肥料上节省数十亿美元，并减少全球环境污染。这需要了解植物中维持这些养分内稳态的分子调节剂。以前，我们报告说氮限制适应（NLA）基因参与拟南芥对低氮条件的适应性反应，其中 nla 突变体植物表现出突然的早期衰老。为了理解 NLA 功能的分子机制，分离到了两个 nla 突变的抑制子，使 nla 突变体的表型恢复为野生型。基于图谱的克隆将这些抑制子鉴定为与磷酸盐（Pi）转运相关的基因 PHF1 和 PHT1.1。此外，NLA 表达受低 Pi 诱导的 microRNA miR827 调控。Pi 分析表明，nla 突变体植物的早期衰老是由于 Pi 毒性。这些植物在硝酸盐低和 Pi 高但硝酸盐高的条件下，特别是在硝酸盐低和 Pi 高的条件下， shoots 中积累的 Pi 含量是正常水平的五倍以上。此外，类似于 nla 突变体，Pi 超积累突变体 pho2 也以硝酸盐依赖的方式表现出 Pi 毒性。此外，硝酸盐和 Pi 水平显示出拮抗的串扰，如它们对开花时间的不同影响所显示的那样。结果表明，NLA 和 miR827 在硝酸盐依赖的方式下在调节植物的 Pi 内稳态方面起着关键作用。
