BACKGROUND AND AIMS The brittle rachis trait is a feature of many wild grasses, particularly within the Triticeae tribe. Wild Hordeum and Triticum species form a disarticulation layer above the rachis node, resulting in the production of wedge type dispersal units. In Aegilops longissima, only one or two of the nodes in the central portion of its rachis are brittle. In the Triticeae species, the formation of a disarticulation layer above the rachis node requires the co-transcription of the two dominant and complementary genes Btr1 and Btr2. This study aims to establish whether homologs of Btr1 and/or Btr2 underlie the unusual brittle rachis phenotype observed in Ae. longissima. METHODS Scanning electron microscopy was used to examine the disarticulation surfaces. Quantitative RT-PCR and RNA in situ hybridization experiments were employed to identify the gene expression in the immature inflorescence. KEY RESULTS An analysis based on scanning electron microscopy was able to demonstrate that the disarticulation surfaces formed in the Ae. longissima rachis are morphologically indistinguishable from those formed in the rachises of wild Hordeum and the Triticum species. An RNA in situ hybridization experiment was able to identify that in the immature Ae. longissima inflorescence, the intensity of Btr1 transcription varied from high at the rachis base to low at its apex, while that of Btr2 was limited to the nodes in the central to distal portion of the rachis. CONCLUSIONS The disarticulation pattern shown by Ae. longissima results from the limitation of Btr1 and Btr2 co-expression to nodes lying in the center of the rachis.

中文翻译：

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Aegilops longissima 轴中形成的独特脱节层可能是 Btr1 和 Btr2 空间共表达的结果

背景和目的 脆轴性状是许多野草的特征，特别是在小麦科部落中。野生大麦属和小麦属在轴节上方形成脱节层，从而产生楔形分散单元。在 Aegilops longissima 中，其轴中心部分的节中只有一两个是脆的。在小麦科物种中，轴节上方脱节层的形成需要两个显性和互补基因 Btr1 和 Btr2 的共同转录。本研究旨在确定 Btr1 和/或 Btr2 的同源物是否是在 Ae 中观察到的异常脆性轴表型的基础。最长的 方法扫描电子显微镜用于检查脱节表面。采用定量RT-PCR和RNA原位杂交实验来鉴定未成熟花序中的基因表达。主要结果 基于扫描电子显微镜的分析能够证明在 Ae 中形成了脱节表面。longissima rachis 在形态上与野生大麦和小麦种的轴中形成的那些没有区别。RNA 原位杂交实验能够在未成熟的 Ae 中识别出它。在 longissima 花序中，Btr1 的转录强度从轴基部的高到其顶点的低不等，而 Btr2 的转录强度仅限于轴中央到远端的节点。结论 Ae 显示的脱音模式。