MAIN CONCLUSION Cytogenomic characterization of Erythrostemon hughesii reveals a heterogeneity of repeats in its subtelomeric heterochromatin. Comparative analyses with other Caesalpinia group species reveal a significant reduction in the abundance of Ty3-gypsy/Chromovirus Tekay retrotransposons during its evolution. In numerically stable karyotypes, repetitive DNA variability is one of the main causes of genome and chromosome variation and evolution. Species from the Caesalpinia group (Leguminosae) are karyotypically characterized by 2n = 24, with small chromosomes and highly variable CMA+ heterochromatin banding patterns that correlate with environmental variables. Erythrostemon hughesii differs from other species of the group examined to date for having subtelomeric CMA+ bands; this contrasts with most species in the group which have proximal bands. Here we analyse the repeatome of E. hughesii using genome skimming and chromosomal mapping approaches to characterize the identity of the most abundant repetitive elements and their physical location. The repetitive fraction of E. hughesii comprises 28.73% of the genome. The most abundant elements were retrotransposons (RT) with long terminal repeats (LTR-RT; 9.76%) and satellite DNAs (7.83%). Within the LTR-RTs, the most abundant lineages were: Ty1/copia-Ale (1%), Ty3/gypsy CRM (0.88%) and Ty3/gypsy Athila (0.75%). Using fluorescent in situ hybridization four satellite DNAs and several LTR-RT elements were shown to be present in most subtelomeric CMA+ bands. These results highlight how the repeatome in E. hughesii, a species from Oaxaca state in Mexico, is clearly distinct from Northeast Brazilian species of the Caesalpinia group, mainly due to its high diversity of repeats in its subtelomeric heterochromatic bands and low amount of LTR-RT Ty3/gypsy-Tekay elements. Comparative sequence analysis of Tekay elements from different species is congruent with a clade-specific origin of this LTR-RT after the divergence of the Caesalpinia group. We hypothesize that repeat-rich heterochromatin may play a role in leading to faster genomic divergence between individuals, increasing speciation and diversification.

中文翻译：

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Caesalpinia 组中的异染色质有多多样化？Erythrostemon Hughesii Gagnon 和 GP Lewis 的细胞基因组学特征（豆科：Caesalpinioideae）

主要结论 Erythrostemon Hughesii 的细胞基因组学特征揭示了其亚端粒异染色质中重复序列的异质性。与其他 Caesalpinia 组物种的比较分析表明，在其进化过程中，Ty3-gypsy/Chromovirus Tekay 反转录转座子的丰度显着降低。在数值稳定的核型中，重复的 DNA 变异是基因组和染色体变异和进化的主要原因之一。Caesalpinia 组（豆科）的物种的核型特征为 2n = 24，具有小染色体和与环境变量相关的高度可变的 CMA+ 异染色质条带模式。Erythrostemon Hughesii 与迄今为止检查过的其他物种的亚端粒 CMA+ 条带不同；这与该组中具有近端带的大多数物种形成对比。在这里，我们使用基因组略读和染色体作图方法分析 E. hughesii 的重复组，以表征最丰富的重复元素的身份及其物理位置。E. hughesii 的重复部分占基因组的 28.73%。最丰富的元素是具有长末端重复序列的反转录转座子 (RT) (LTR-RT; 9.76%) 和卫星 DNA (7.83%)。在 LTR-RTs 中，最丰富的谱系是：Ty1/copia-Ale (1%)、Ty3/gypsy CRM (0.88%) 和 Ty3/gypsy Athila (0.75%)。使用荧光原位杂交，四个卫星 DNA 和几个 LTR-RT 元件被证明存在于大多数亚端粒 CMA+ 带中。这些结果突出了来自墨西哥瓦哈卡州的 E.hughesii 的重复组如何，明显不同于 Caesalpinia 组的巴西东北部物种，主要是由于其亚端粒异色带中重复的高度多样性和 LTR-RT Ty3 / gypsy-Tekay 元素的含量低。在 Caesalpinia 组分歧后，来自不同物种的 Tekay 元素的比较序列分析与该 LTR-RT 的进化枝特异性起源一致。我们假设重复丰富的异染色质可能在导致个体之间更快的基因组分化、增加物种形成和多样化方面发挥作用。在 Caesalpinia 组分歧后，来自不同物种的 Tekay 元素的比较序列分析与该 LTR-RT 的进化枝特异性起源一致。我们假设重复丰富的异染色质可能在导致个体之间更快的基因组分化、增加物种形成和多样化方面发挥作用。在 Caesalpinia 组分歧后，来自不同物种的 Tekay 元素的比较序列分析与该 LTR-RT 的进化枝特异性起源一致。我们假设重复丰富的异染色质可能在导致个体之间更快的基因组分化、增加物种形成和多样化方面发挥作用。