Xue et al. describe a phenomenon in maize and its nearest wild relative, teosinte, by which backcross progeny of a specific teosinte and maize exhibit a sickly whole-plant phenotype involving changes in morphology, vigor, and viability... In the course of generating populations of maize with teosinte chromosomal introgressions, an unusual sickly plant phenotype was noted in individuals from crosses with two teosinte accessions collected near Valle de Bravo, Mexico. The plants of these Bravo teosinte accessions appear phenotypically normal themselves and the F1 plants appear similar to typical maize × teosinte F1s. However, upon backcrossing to maize, the BC1 and subsequent generations display a number of detrimental characteristics including shorter stature, reduced seed set, and abnormal floral structures. This phenomenon is observed in all BC individuals and there is no chromosomal segment linked to the sickly plant phenotype in advanced backcross generations. Once the sickly phenotype appears in a lineage, normal plants are never again recovered by continued backcrossing to the normal maize parent. Whole-genome shotgun sequencing reveals a small number of genomic sequences, some with homology to transposable elements, that have increased in copy number in the backcross populations. Transcriptome analysis of seedlings, which do not have striking phenotypic abnormalities, identified segments of 18 maize genes that exhibit increased expression in sickly plants. A de novo assembly of transcripts present in plants exhibiting the sickly phenotype identified a set of 59 upregulated novel transcripts. These transcripts include some examples with sequence similarity to transposable elements and other sequences present in the recurrent maize parent (W22) genome as well as novel sequences not present in the W22 genome. Genome-wide profiles of gene expression, DNA methylation, and small RNAs are similar between sickly plants and normal controls, although a few upregulated transcripts and transposable elements are associated with altered small RNA or methylation profiles. This study documents hybrid incompatibility and genome instability triggered by the backcrossing of Bravo teosinte with maize. We name this phenomenon "hybrid decay" and present ideas on the mechanism that may underlie it.

中文翻译：

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杂种衰变：类蜀黍与玉米回交群体中引发的活力和活力的跨代表观遗传下降。


薛等人。描述了玉米及其最近的野生近缘种类蜀黍中的一种现象，通过这种现象，特定类蜀黍和玉米的回交后代表现出病态的全株表型，涉及形态、活力和活力的变化……在产生玉米种群的过程中墨西哥巴耶德布拉沃附近收集的两种类蜀黍品种的杂交个体中，由于类蜀黍染色体渗入，发现了一种不寻常的病态植物表型。这些 Bravo 类蜀黍种质的植物本身表型正常，F1 植物看起来与典型的玉米 × 类蜀黍 F1 相似。然而，在与玉米回交后，BC1 及其后代表现出许多有害特征，包括身材矮小、结实率降低和花结构异常。这种现象在所有 BC 个体中都观察到，并且在高级回交世代中不存在与病态植物表型相关的染色体片段。一旦谱系中出现病态表型，通过与正常玉米亲本继续回交就再也无法恢复正常植物。全基因组鸟枪法测序揭示了少量基因组序列，其中一些与转座元件具有同源性，这些序列在回交群体中的拷贝数有所增加。对没有显着表型异常的幼苗进行转录组分析，鉴定出 18 个玉米基因的片段在患病植物中表现出表达增加。对表现出病态表型的植物中存在的转录本进行从头组装，鉴定出一组 59 个上调的新转录本。 这些转录物包括一些与转座元件和轮回玉米亲本（W22）基因组中存在的其他序列具有序列相似性的例子，以及W22基因组中不存在的新序列。尽管一些上调的转录物和转座元件与改变的小RNA或甲基化谱相关，但患病植物和正常对照之间的基因表达、DNA甲基化和小RNA的全基因组谱相似。这项研究记录了 Bravo 类蜀黍与玉米回交引发的杂交不相容性和基因组不稳定。我们将这种现象命名为“混合衰变”，并提出了关于其背后机制的想法。