State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Innovation Academy for Seed Design, Chinese Academy of Sciences, Beijing, 100101, China.
College of Agriculture, Yangtze University, Jingzhou, 434000, Hubei, China.
BMC Genomics. 2021 Jan 14;22(1):55. doi: 10.1186/s12864-020-07364-6.
During the bread wheat speciation by polyploidization, a series of genome rearrangement and sequence recombination occurred. Simple sequence repeat (SSR) sequences, predominately located in heterochromatic regions of chromosomes, are the effective marker for tracing the genomic DNA sequence variations. However, to date the distribution dynamics of SSRs on chromosomes of bread wheat and its donors, including diploid and tetraploid Triticum urartu, Aegilops speltoides, Aegilops tauschii, Triticum turgidum ssp. dicocoides, reflecting the genome evolution events during bread wheat formation had not been comprehensively investigated.
The genome evolution was studied by comprehensively comparing the distribution patterns of (AAC), (AAG), (AGC) and (AG) in bread wheat Triticum aestivum var. Chinese Spring and its progenitors T. urartu, A. speltoides, Ae. tauschii, wild tetroploid emmer wheat T. dicocoides, and cultivated emmer wheat T. dicoccum. Results indicated that there are specific distribution patterns in different chromosomes from different species for each SSRs. They provided efficient visible markers for identification of some individual chromosomes and SSR sequence evolution tracing from the diploid progenitors to hexaploid wheat. During wheat speciation, the SSR sequence expansion occurred predominately in the centromeric and pericentromeric regions of B genome chromosomes accompanied by little expansion and elimination on other chromosomes. This result indicated that the B genome might be more sensitive to the "genome shock" and more changeable during wheat polyplodization.
During the bread wheat evolution, SSRs including (AAC), (AAG), (AGC) and (AG) in B genome displayed the greatest changes (sequence expansion) especially in centromeric and pericentromeric regions during the polyploidization from Ae. speltoides S genome, the most likely donor of B genome. This work would enable a better understanding of the wheat genome formation and evolution and reinforce the viewpoint that B genome was originated from S genome.
在小麦属通过多倍体化形成过程中，发生了一系列基因组重排和序列重组。简单重复序列（SSR）序列主要位于染色体的异染色质区域，是追踪基因组 DNA 序列变异的有效标记。然而，迄今为止，还没有全面研究 SSR 在小麦及其供体二倍体乌拉尔图小麦、粗山羊草、节节麦、密穗小麦和栽培一粒小麦中的染色体上的分布动态，这些供体反映了小麦形成过程中的基因组进化事件。
通过综合比较普通小麦中国春及其二倍体祖先乌拉尔图小麦、粗山羊草、节节麦、野生六倍体密穗小麦和栽培一粒小麦中（AAC）、（AAG）、（AGC）和（AG）的分布模式，研究了基因组的进化。结果表明，每个 SSR 在不同物种的不同染色体上都有特定的分布模式。它们为鉴定个别染色体和从二倍体祖先到六倍体小麦的 SSR 序列进化提供了有效的可见标记。在小麦形成过程中，SSR 序列主要在 B 基因组染色体的着丝粒和着丝粒周围区域扩张，而其他染色体的扩张和消除较少。这表明 B 基因组在小麦多倍化过程中可能对“基因组冲击”更为敏感，变化也更大。
在普通小麦的进化过程中，B 基因组中的（AAC）、（AAG）、（AGC）和（AG）等 SSR 发生了最大的变化（序列扩张），尤其是在多倍体化过程中来自粗山羊草 S 基因组的 B 基因组，这是 B 基因组最有可能的供体。这项工作将有助于更好地理解小麦基因组的形成和进化，并加强 B 基因组起源于 S 基因组的观点。
