Plant Biology Major, Iowa State University, 253 Horticulture Hall, Ames, IA 50011-1100, USA.
Planta. 2012 Dec;236(6):1747-55. doi: 10.1007/s00425-012-1726-7. Epub 2012 Aug 7.
Polypyrimidine tract-binding (PTB) proteins are RNA-binding proteins that target specific RNAs for post-transcriptional processing by binding cytosine/uracil motifs. PTBs have established functions in a range of RNA processes including splicing, translation, stability and long-distance transport. Six PTB-like genes identified in potato have been grouped into two clades based on homology to other known plant PTBs. StPTB1 and StPTB6 are closely related to a PTB protein discovered in pumpkin, designated CmRBP50, and contain four canonical RNA-recognition motifs. CmRBP50 is expressed in phloem tissues and functions as the core protein of a phloem-mobile RNA/protein complex. Sequence from the potato genome database was used to clone the upstream sequence of these two PTB genes and analyzed to identify conserved cis-elements. The promoter of StPTB6 was enriched for regulatory elements for light and sucrose induction and defense. Upstream sequence of both PTB genes was fused to β-glucuronidase and monitored in transgenic potato lines. In whole plants, the StPTB1 promoter was most active in leaf veins and petioles, whereas StPTB6 was most active in leaf mesophyll. Both genes are active in new tubers and tuber sprouts. StPTB6 expression was induced in stems and stolon sections in response to sucrose and in leaves or petioles in response to light, heat, drought and mechanical wounding. These results show that CmRBP50-like genes of potato exhibit distinct expression patterns and respond to both developmental and environmental cues.
多嘧啶核苷酸结合（PTB）蛋白是 RNA 结合蛋白，通过结合胞嘧啶/尿嘧啶基序，靶向特定的 RNA 进行转录后加工。PTB 在一系列 RNA 过程中具有重要功能，包括剪接、翻译、稳定性和长距离运输。在马铃薯中鉴定的六个 PTB 样基因根据与其他已知植物 PTB 的同源性分为两个分支。StPTB1 和 StPTB6 与在南瓜中发现的一种称为 CmRBP50 的 PTB 蛋白密切相关，并且包含四个典型的 RNA 识别基序。CmRBP50 在韧皮部组织中表达，作为韧皮部移动 RNA/蛋白复合物的核心蛋白发挥作用。使用来自马铃薯基因组数据库的序列克隆了这两个 PTB 基因的上游序列，并对其进行了分析以鉴定保守的顺式元件。StPTB6 的启动子富含光和蔗糖诱导和防御的调节元件。两个 PTB 基因的上游序列均与β-葡萄糖醛酸酶融合，并在转基因马铃薯品系中进行监测。在整个植物中，StPTB1 启动子在叶片叶脉和叶柄中活性最高，而 StPTB6 在叶片叶肉中活性最高。两个基因在新块茎和块茎芽中均有活性。StPTB6 的表达在茎和匍匐茎节段中响应蔗糖诱导，在叶片或叶柄中响应光、热、干旱和机械损伤诱导。这些结果表明，马铃薯中 CmRBP50 样基因表现出不同的表达模式，并对发育和环境线索均有响应。
