Institute of Crop Science, National Agriculture and Food Research Organization (NARO), Tsukuba, Japan.
Graduate School of Horticulture, Chiba University, Matsudo, Chiba, Japan.
Ann Bot. 2021 Feb 9;127(3):297-304. doi: 10.1093/aob/mcaa147.
The brittle rachis trait is a feature of many wild grasses, particularly within the tribe Triticeae. 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 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 homologues of Btr1 and/or Btr2 underlie the unusual brittle rachis phenotype observed in Ae. longissima.
Scanning electron microscopy was used to examine the disarticulation surfaces. Quantitative RT-PCR and RNA in situ hybridization experiments were used to identify gene expression in the immature inflorescence.
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 Triticum species. RNA in situ hybridization showed 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.
The disarticulation pattern shown by Ae. longissima results from the limitation of Btr1 and Btr2 co-expression to nodes lying in the centre of the rachis.
脆弱颖果稃是许多野生禾本科植物的特征，尤其是在小麦族中。野生大麦和小麦属物种在颖果节间上方形成一个离层，导致楔形散布单位的产生。在长穗偃麦草中，只有颖果稃中心部分的一个或两个节间是脆弱的。在小麦族中，颖果节间上方离层的形成需要两个主效互补基因 Btr1 和 Btr2 的共转录。本研究旨在确定 Ae. longissima 中观察到的异常脆弱颖果表型是否由 Btr1 和/或 Btr2 的同源物引起。
扫描电子显微镜用于检查离层表面。定量 RT-PCR 和 RNA 原位杂交实验用于鉴定未成熟花序中的基因表达。
基于扫描电子显微镜的分析能够证明 Ae. longissima 颖果中形成的离层表面在形态上与野生大麦和小麦属物种的颖果离层表面无法区分。RNA 原位杂交显示，在未成熟的 Ae. longissima 花序中，Btr1 转录的强度从颖果基部的高到顶端的低变化，而 Btr2 的强度仅限于颖果中部到远端节间的节点。
Ae. longissima 显示的离层模式是由于 Btr1 和 Btr2 共表达限于颖果中部的节点所致。
