Abstract：
CONCLUSIONS: Nitrate uptake in sugarcane roots is regulated at the transcriptional and posttranscriptional levels based on the physiological status of the plant and is likely a determinant mechanism for discrimination against nitrate. Sugarcane (Saccharum spp.) is one of the most suitable energy crops for biofuel feedstock, but the reduced recovery of nitrogen (N) fertilizer by sugarcane roots increases the crop carbon footprint. The low nitrogen use efficiency (NUE) of sugarcane has been associated with the significantly low nitrate uptake, which limits the utilization of the large amount of nitrate available in agricultural soils. To understand the regulation of nitrate uptake in sugarcane roots, we identified the major canonical nitrate transporter genes (NRTs-NITRATE TRANSPORTERS) and then determined their expression profiles in roots under contrasting N conditions. Correlation of gene expression with 15N-nitrate uptake revealed that under N deprivation or inorganic N (ammonium or nitrate) supply in N-sufficient roots, the regulation of ScNRT2.1 and ScNRT3.1 expression is the predominant mechanism for the modulation of the activity of the nitrate high-affinity transport system. Conversely, in N-deficient roots, the induction of ScNRT2.1 and ScNRT3.1 transcription is not correlated with the marked repression of nitrate uptake in response to nitrate resupply or high N provision, which suggested the existence of a posttranscriptional regulatory mechanism. Our findings suggested that high-affinity nitrate uptake is regulated at the transcriptional and presumably at the posttranscriptional levels based on the physiological N status and that the regulation of NRT2.1 and NRT3.1 activity is likely a determinant mechanism for the discrimination against nitrate uptake observed in sugarcane roots, which contributes to the low NUE in this crop species.
摘要：
结论：基于植物的生理状态，甘蔗根中硝酸盐的吸收在转录和转录后水平上受到调节，并且可能是区分硝酸盐的决定机制。甘蔗（甘蔗属。)是最适合用作生物燃料原料的能源作物之一，但是甘蔗根对氮（N）肥料的回收率降低会增加作物的碳足迹。甘蔗的低氮利用效率(NUE)与显著低的硝酸盐吸收有关,这限制了农业土壤中可用的大量硝酸盐的利用。为了解甘蔗根系硝酸盐吸收规律,我们确定了主要的典型硝酸盐转运蛋白基因（NRT-NitrateTransporters），然后在对比的N条件下确定了它们在根中的表达谱。基因表达与15N硝酸盐吸收的相关性表明，在氮剥夺或无机氮（铵或硝酸盐）供应下，ScNRT2.1和ScNRT3.1表达的调节是调节硝酸盐高亲和力转运系统活性的主要机制。相反，在缺氮的根中，ScNRT2.1和ScNRT3.1转录的诱导与响应硝酸盐再供应或高氮供应的硝酸盐摄取的显著抑制无关，这表明了转录后调控机制的存在。我们的发现表明，基于生理N状态，高亲和力硝酸盐的吸收在转录水平和转录后水平受到调节，并且NRT2.1和NRT3.1活性的调节可能是区分观察到的硝酸盐吸收的决定机制在甘蔗根中，这有助于该作物种类的低NUE。
