Department of Plant Sciences, North Dakota State University, Fargo, ND, 58108, USA.
Present address: National Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, People's Republic of China.
BMC Plant Biol. 2018 Oct 11;18(1):224. doi: 10.1186/s12870-018-1442-y.
Meiosis is a specialized cell division critical for gamete production in the sexual reproduction of eukaryotes. It ensures genome integrity and generates genetic variability as well. The Rec8-like cohesin is a cohesion protein essential for orderly chromosome segregation in meiotic cell division. The Rec8-like genes and cohesins have been cloned and characterized in diploid models, but not in polyploids. The present study aimed to clone the homoeologous genes (homoeoalleles) for Rec8-like cohesin in polyploid wheat, an important food crop for humans, and to characterize their structure and function under a polyploid condition.
We cloned two Rec8-like homoeoalleles from tetraploid wheat (TtRec8-A1 and TtRec8-B1) and one from hexaploid wheat (TaRec8-D1), and performed expression and functional analyses of the homoeoalleles. Also, we identified other two Rec8 homoeoalleles in hexaploid wheat (TaRec8-A1 and TaRec8-B1) and the one in Aegilops tauschii (AetRec8-D1) by referencing the DNA sequences of the Rec8 homoeoalleles cloned in this study. The coding DNA sequences (CDS) of these six Rec8 homoeoalleles are all 1,827 bp in length, encoding 608 amino acids. They differed from each other primarily in introns although single nucleotide polymorphisms were detected in CDS. Substantial difference was observed between the homoeoalleles from the subgenome B (TtRec8-B1 and TaRec8-B1) and those from the subgenomes A and D (TtRec8-A1, TaRec8-A1, and TaRec8-D1). TtRec8-A1 expressed dominantly over TtRec8-B1, but comparably to TaRec8-D1, in polyploid wheat. In addition, we developed the antibody against wheat Rec8 and used the antibody to detect Rec8 cohesin in the Western blotting and subcellular localization analyses.
The Rec8 homoeoalleles from the subgenomes A and D are transcriptionally more active than the one from the subgenome B in polyploid wheat. The structural variation and differential expression of the Rec8 homoeoalleles indicate a unique cross-genome coordination of the homoeologous genes in polyploid wheat, and imply the distinction of the wheat subgenome B from the subgenomes A and D in the origin and evolution.
减数分裂是真核生物有性生殖中配子产生所必需的一种特殊细胞分裂。它确保了基因组的完整性，并产生了遗传变异性。Rec8 样黏合蛋白是有丝分裂细胞分裂中有序染色体分离所必需的黏合蛋白。Rec8 样基因和黏合蛋白已在二倍体模型中被克隆和表征，但在多倍体中尚未被克隆和表征。本研究旨在克隆多倍体小麦（人类重要的粮食作物）中 Rec8 样黏合蛋白的同源基因（同系等位基因），并在多倍体条件下对其结构和功能进行表征。
我们从四倍体小麦（TtRec8-A1 和 TtRec8-B1）中克隆了两个 Rec8 样同系等位基因，从六倍体小麦（TaRec8-D1）中克隆了一个，对同系等位基因进行了表达和功能分析。此外，我们通过参考本研究中克隆的 Rec8 同系等位基因的 DNA 序列，在六倍体小麦中鉴定了另外两个 Rec8 同系等位基因（TaRec8-A1 和 TaRec8-B1）和在节节麦中鉴定了一个（AetRec8-D1）。这六个 Rec8 同系等位基因的编码 DNA 序列（CDS）均为 1827bp，编码 608 个氨基酸。它们主要在内含子中存在差异，尽管在 CDS 中也检测到了单核苷酸多态性。亚基因组 B（TtRec8-B1 和 TaRec8-B1）的同系等位基因与亚基因组 A 和 D（TtRec8-A1、TaRec8-A1 和 TaRec8-D1）的同系等位基因之间存在显著差异。在多倍体小麦中，TtRec8-A1 的表达量明显高于 TtRec8-B1，但与 TaRec8-D1 相当。此外，我们开发了针对小麦 Rec8 的抗体，并使用该抗体在 Western blot 和亚细胞定位分析中检测 Rec8 黏合蛋白。
多倍体小麦中，亚基因组 A 和 D 的 Rec8 同系等位基因的转录活性高于亚基因组 B 的 Rec8 同系等位基因。Rec8 同系等位基因的结构变异和差异表达表明，多倍体小麦中同源基因的跨基因组协调具有独特性，并暗示了小麦亚基因组 B 与亚基因组 A 和 D 在起源和进化上的区别。
