Maize exhibits marked growth and yield response to supplemental nitrogen (N). Here, we report the functional characterization of a maize NIN-like protein ZmNLP5 as a central hub in a molecular network associated with N metabolism. Predominantly expressed and accumulated in roots and vascular tissues, ZmNLP5 was shown to rapidly respond to nitrate treatment. Under limited N supply, compared with that of wild-type (WT) seedlings, the zmnlp5 mutant seedlings accumulated less nitrate and nitrite in the root tissues and ammonium in the shoot tissues. The zmnlp5 mutant plants accumulated less nitrogen than the WT plants in the ear leaves and seed kernels. Furthermore, the mutants carrying the transgenic ZmNLP5 cDNA fragment significantly increased the nitrate content in the root tissues compared with that of the zmnlp5 mutants. In the zmnlp5 mutant plants, loss of the ZmNLP5 function led to changes in expression for a significant number of genes involved in N signalling and metabolism. We further show that ZmNLP5 directly regulates the expression of nitrite reductase 1.1 (ZmNIR1.1) by binding to the nitrate-responsive cis-element at the 5' UTR of the gene. Interestingly, a natural loss-of-function allele of ZmNLP5 in Mo17 conferred less N accumulation in the ear leaves and seed kernels resembling that of the zmnlp5 mutant plants. Our findings show that ZmNLP5 is involved in mediating the plant response to N in maize.

中文翻译：

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NIN样蛋白5（ZmNLP5）转录因子参与调节玉米的氮响应。

玉米对补充氮（N）表现出明显的生长和产量响应。在这里，我们报告玉米NIN样蛋白ZmNLP5作为与N代谢相关的分子网络的中心枢纽的功能表征。ZmNLP5主要在根和维管组织中表达和积累，显示对硝酸盐处理有快速反应。在有限的氮供应下，与野生型（WT）幼苗相比，zmnlp5突变型幼苗在根组织中积累的硝酸盐和亚硝酸盐较少，在芽组织中积累的铵较少。zmnlp5突变植株在穗叶和种子仁中积累的氮含量比野生型植株少。此外，与zmnlp5突变体相比，携带转基因ZmNLP5 cDNA片段的突变体显着增加了根组织中的硝酸盐含量。在zmnlp5突变植物中，ZmNLP5功能的丧失导致涉及N信号传导和代谢的大量基因的表达发生变化。我们进一步显示ZmNLP5通过与基因5'UTR上的硝酸盐反应性顺式元件结合，直接调节亚硝酸还原酶1.1（ZmNIR1.1）的表达。有趣的是，Mo17中ZmNLP5的自然功能丧失等位基因赋予了与zmnlp5突变植物相似的较少的N积累在穗叶和种子仁中。我们的发现表明ZmNLP5参与介导玉米中植物对N的反应。1）通过在基因的5'UTR结合硝酸盐反应性顺式元件。有趣的是，Mo17中ZmNLP5的自然功能丧失等位基因赋予了与zmnlp5突变植物相似的较少的N积累在穗叶和种子仁中。我们的发现表明ZmNLP5参与介导玉米中植物对N的反应。1）通过在基因的5'UTR结合硝酸盐反应性顺式元件。有趣的是，Mo17中ZmNLP5的自然功能丧失等位基因赋予了与zmnlp5突变植物相似的较少的N积累在穗叶和种子仁中。我们的发现表明ZmNLP5参与介导玉米中植物对N的反应。