Abstract Hordeum vulgare and Hordeum bulbosum are two closely related barley species, which share a common H genome. H. vulgare has two nucleolar organizer regions (NORs), while the NOR of H. bulbosum is only one. We sequenced the 2.5 kb 25S-18S region in the rDNA of H. bulbosum and compared it to the same region in H. vulgare as well as to the other Triticeae. The region includes an intergenic spacer (IGS) with a number of subrepeats, a promoter, and an external transcribed spacer (5′ETS). The IGS of H. bulbosum downstream of 25S rRNA contains two 143-bp repeats and six 128-bp repeats. In contrast, the IGS in H. vulgare contains an array of seven 79-bp repeats and a varying number of 135-bp repeats. The 135-bp repeats in H. vulgare and the 128-bp repeats in H. bulbosum show similarity. Compared to H. vulgare, the 5′ETS of H. bulbosum is shorter. Additionally, the 5′ETS regions in H. bulbosum and H. vulgare diverged faster than in other Triticeae genera. Alignment of the Triticeae promoter sequences suggests that in Hordeum, as in diploid Triticum, transcription starts with guanine and not with adenine as it is in many other plants.

中文翻译：

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球茎大麦 25S-18S rDNA 区域：与大麦和其他小麦科的比较

摘要 Hordeum vulgare 和Hordeumbulbosum 是两个密切相关的大麦物种，它们共享一个共同的H 基因组。H. vulgare 有两个核仁组织区 (NOR)，而 H.bulbosum 的 NOR 只有一个。我们对 H.bulbosum 的 rDNA 中的 2.5 kb 25S-18S 区域进行了测序，并将其与 H. vulgare 以及其他小麦科的相同区域进行了比较。该区域包括具有多个亚重复的基因间间隔区 (IGS)、启动子和外部转录间隔区 (5'ETS)。H.bulbosum 25S rRNA 下游的 IGS 包含两个 143-bp 重复和六个 128-bp 重复。相比之下，H. vulgare 中的 IGS 包含七个 79-bp 重复序列和不同数量的 135-bp 重复序列。H. vulgare 中的 135-bp 重复和 H.bulbosum 中的 128-bp 重复显示相似性。与 H. vulgare 相比，H.bulbosum 的 5'ETS 较短。此外，H.bulbosum 和 H. vulgare 的 5'ETS 区域比其他小麦属的分化速度更快。小麦科启动子序列的比对表明，在大麦中，就像在二倍体小麦中一样，转录从鸟嘌呤开始，而不是像在许多其他植物中那样从腺嘌呤开始。