Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki 036-8561, Japan.
Plant Cell Rep. 2011 Sep;30(9):1723-33. doi: 10.1007/s00299-011-1080-4. Epub 2011 May 11.
Companion cells are metabolically active and functionally specialized cells that behave as terminals for the transport of materials between phloem and the surrounding tissue. Although previous research has clarified the distinct function of companion cells, it is still largely unknown how plants establish and maintain the special identity of these cells. To shed further light on this issue, we carried out expressed sequence tag (EST) analysis. To minimize the difficulty of dissociating and gathering intact companion cells, vascular strings with an abundant content of companion cells were excised from the petioles of Brassica napus. By random sequencing with a string-specific cDNA library derived by suppression subtractive hybridization between the string itself and the petiole from which it had been removed, we identified 377 ESTs and assembled them into 247 EST groups. The most frequent EST was ExBdl-102 (15 of 377 ESTs), which showed the highest sequence similarity to the Arabidopsis CORI3 (CORONATINE INDUCED 3) gene. The CORI3 promoter:GUS showed predominant expression in the vascular tissue of Arabidopsis. Through transient expression assay using Brassica vasculature and gene-gun-mediated transient assay, we found two integrated cis-regulatory regions of the CORI3 promoter. This work has provided not only string-specific EST information and shown that two novel cis-regulatory regions sustain transcriptional activity in companion cells, but also a series of procedures for efficiently examining the transcriptional framework of companion cells by exploiting the histochemical advantage of B. napus as an experimental material.
伴胞是代谢活跃且功能特化的细胞，它们作为韧皮部和周围组织之间物质运输的终端。尽管先前的研究已经阐明了伴胞的独特功能，但植物如何建立和维持这些细胞的特殊身份在很大程度上仍然未知。为了进一步阐明这个问题，我们进行了表达序列标签（EST）分析。为了最大限度地减少分离和收集完整伴胞的困难，我们从油菜叶柄中切取富含伴胞的维管束。通过用维管束自身与去除维管束的叶柄之间的抑制性消减杂交衍生的维管束特异性 cDNA 文库进行随机测序，我们鉴定了 377 个 EST，并将它们组装成 247 个 EST 组。最频繁的 EST 是 ExBdl-102（377 个 EST 中的 15 个），它与拟南芥 CORI3（CORONATINE INDUCED 3）基因的序列相似度最高。CORI3 启动子：GUS 在拟南芥的维管束组织中表现出强烈的表达。通过使用油菜维管束进行瞬时表达测定和基因枪介导的瞬时测定，我们发现了 CORI3 启动子的两个整合顺式调控区。这项工作不仅提供了维管束特异性的 EST 信息，并表明两个新的顺式调控区维持了伴胞中的转录活性，而且还提供了一系列通过利用油菜作为实验材料的组织化学优势来有效检查伴胞转录框架的程序。
