Trevisan S, Borsa P, Botton A, Varotto S, Malagoli M, Ruperti B, Quaggiotti S
Department of Agricultural Biotechnology, University of Padova, Legnaro, Italy.
Plant Biol (Stuttg). 2008 Jul;10(4):462-75. doi: 10.1111/j.1438-8677.2008.00041.x.
A full-length cDNA encoding a putative high-affinity nitrate transporter (ZmNrt2.2) from maize was isolated and characterised, together with another previously identified transporter (ZmNrt2.1), in terms of phylogenesis, protein structure prediction and regulation of transcript accumulation in response to nitrate and sugar availability. The expression of both genes was evaluated by quantitative and semi-quantitative RT-PCR in response to nitrate and sugar supply and the in planta localisation of mRNA was studied by in situ hybridisation. Data obtained suggested similar genetic evolution and identical transmembrane structure prediction between the two deduced proteins, and differences in both regulation of their expression and mRNA localisation in response to nitrate, leading us to hypothesise a principal role for ZmNRT2.1 in the influx activity and the major involvement of ZmNRT2.2 in the xylem loading process. Our data suggest opposing sugar regulation by ZmNrt2.1 and ZmNrt2.2 transcription in the presence or absence of nitrate and the existence of both hexokinase-dependent and hexokinase-independent transduction mechanisms for the regulation of ZmNrt2.1 and ZmNrt2.2 expression by sugars.
从玉米中分离并鉴定了一个编码假定高亲和力硝酸盐转运蛋白（ZmNrt2.2）的全长cDNA，以及另一个先前鉴定的转运蛋白（ZmNrt2.1），并从系统发育、蛋白质结构预测以及响应硝酸盐和糖分可利用性时转录积累的调控等方面进行了研究。通过定量和半定量RT-PCR评估了这两个基因对硝酸盐和糖分供应的响应表达，并通过原位杂交研究了mRNA在植物体内的定位。获得的数据表明，这两个推导蛋白之间具有相似的遗传进化和相同的跨膜结构预测，并且它们在响应硝酸盐时的表达调控和mRNA定位存在差异，这使我们推测ZmNRT2.1在流入活性中起主要作用，而ZmNRT2.2主要参与木质部装载过程。我们的数据表明，在有或没有硝酸盐的情况下，ZmNrt2.1和ZmNrt2.2转录对糖分的调控相反，并且存在通过己糖激酶依赖性和己糖激酶非依赖性转导机制来调控ZmNrt2.1和ZmNrt2.2表达的糖分。
