Plant Biology Major, Iowa State University, Ames, Iowa 50011-1100, USA.
Plant Physiol. 2009 Dec;151(4):1831-43. doi: 10.1104/pp.109.144428. Epub 2009 Sep 25.
BEL1-like transcription factors are ubiquitous in plants and interact with KNOTTED1 types to regulate numerous developmental processes. In potato (Solanum tuberosum subsp. andigena), the BEL1-like transcription factor StBEL5 and its Knox protein partner regulate tuber formation by targeting genes that control growth. RNA detection methods and heterografting experiments demonstrated that StBEL5 transcripts are present in phloem cells and move across a graft union to localize in stolon tips, the site of tuber induction. This movement of RNA originates in leaf veins and petioles and is induced by a short-day photoperiod, regulated by the untranslated regions, and correlated with enhanced tuber production. Assays for RNA mobility suggest that both 5' and 3' untranslated regions contribute to the preferential accumulation of the StBEL5 RNA but that the 3' untranslated region may contribute more to transport from the leaf to the stem and into the stolons. Addition of the StBEL5 untranslated regions to another BEL1-like mRNA resulted in its preferential transport to stolon tips and enhanced tuber production. Transcript stability assays showed that the untranslated regions and a long-day photoperiod enhanced StBEL5 RNA stability in shoot tips. Upon fusion of the untranslated regions of StBEL5 to a beta-glucuronidase marker, translation in tobacco (Nicotiana tabacum) protoplasts was repressed by those constructs containing the 3' untranslated sequence. These results demonstrate that the untranslated regions of the mRNA of StBEL5 are involved in mediating its long-distance transport, in maintaining transcript stability, and in controlling translation.
BEL1 样转录因子在植物中普遍存在，与 KNOTTED1 型相互作用，调节众多发育过程。在马铃薯（Solanum tuberosum subsp. andigena）中，BEL1 样转录因子 StBEL5 及其 Knox 蛋白伴侣通过靶向控制生长的基因来调节块茎形成。RNA 检测方法和异质嫁接实验表明，StBEL5 转录本存在于韧皮部细胞中，并通过嫁接结合点移动到块茎诱导部位的匍匐茎尖端。这种 RNA 的移动起源于叶片叶脉和叶柄，并被短日照光周期诱导，受非翻译区调控，并与增强的块茎产量相关。RNA 迁移分析表明，5'和 3'非翻译区都有助于 StBEL5 RNA 的优先积累，但 3'非翻译区可能更有助于从叶片到茎和匍匐茎的运输。将 StBEL5 的非翻译区添加到另一个 BEL1 样 mRNA 中，导致其优先运输到匍匐茎尖端，并增强块茎产量。转录本稳定性分析表明，非翻译区和长日照光周期增强了茎尖中 StBEL5 RNA 的稳定性。当 StBEL5 的非翻译区与β-葡萄糖醛酸酶标记融合时，含有 3'非翻译序列的构建体抑制了烟草（Nicotiana tabacum）原生质体中的翻译。这些结果表明，StBEL5 mRNA 的非翻译区参与介导其长距离运输、维持转录本稳定性和控制翻译。
