Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland.
Planta. 2012 Feb;235(2):311-23. doi: 10.1007/s00425-011-1508-7. Epub 2011 Sep 9.
Members of the peptide transporter/nitrate transporter 1 (PTR/NRT1) family in plants transport a variety of substrates like nitrate, di- and tripepetides, auxin and carboxylates. We isolated two members of this family from Arabidopsis, AtPTR4 and AtPTR6, which are highly homologous to the characterized di- and tripeptide transporters AtPTR1, AtPTR2 and AtPTR5. All known substrates of members of the PTR/NRT1 family were tested using heterologous expression in Saccharomyces cerevisiae mutants and oocytes of Xenopus laevis, but none could be identified as substrate of AtPTR4 or AtPTR6. AtPTR4 and AtPTR6 show distinct expression patterns, while AtPTR4 is expressed in the vasculature of the plants, AtPTR6 is highly expressed in pollen and during senescence. Phylogenetic analyses revealed that AtPTR2, 4 and 6 belong to one clade of subgoup II, whereas AtPTR1 and 5 are found in a second clade. Like AtPTR2, AtPTR4-GFP and AtPTR6-GFP fusion proteins are localized at the tonoplast. Vacuolar localization was corroborated by co-localization of AtPTR2-YFP with the tonoplast marker protein GFP-AtTIP2;1 and AtTIP1;1-GFP. This indicates that the two clades reflect different intracellular localization at the tonoplast (AtPTR2, 4, 6) and plasma membrane (AtPTR1, 5), respectively.
植物中的肽转运蛋白/硝酸盐转运蛋白 1（PTR/NRT1）家族成员可转运多种底物，如硝酸盐、二肽和三肽、生长素和羧酸。我们从拟南芥中分离出该家族的两个成员，AtPTR4 和 AtPTR6，它们与已鉴定的二肽和三肽转运蛋白 AtPTR1、AtPTR2 和 AtPTR5 高度同源。使用异源表达在酿酒酵母突变体和非洲爪蟾卵母细胞中的方法，测试了该 PTR/NRT1 家族所有已知底物，但都不能鉴定为 AtPTR4 或 AtPTR6 的底物。AtPTR4 和 AtPTR6 表现出不同的表达模式，而 AtPTR4 在植物的脉管系统中表达，AtPTR6 在花粉和衰老过程中高度表达。系统发育分析表明，AtPTR2、4 和 6 属于亚组 II 的一个分支，而 AtPTR1 和 5 属于另一个分支。与 AtPTR2 一样，AtPTR4-GFP 和 AtPTR6-GFP 融合蛋白定位于液泡膜上。AtPTR2-YFP 与液泡膜标记蛋白 GFP-AtTIP2;1 和 AtTIP1;1-GFP 的共定位证实了液泡定位。这表明这两个分支分别反映了液泡膜（AtPTR2、4、6）和质膜（AtPTR1、5）上的不同细胞内定位。
