近日，華中農(nóng)業(yè)大學(xué)小麥團(tuán)隊蘇漢東教授課題組在《Molecular Biology and Evolution》雜志發(fā)表了“Centromere plasticity with evolutionary conservation and divergence uncovered by wheat 10+ genomes”的研究論文。該研究通過全球小麥育種計劃10+基因組材料的公共數(shù)據(jù)揭示了小麥著絲粒進(jìn)化多樣性和功能保守性的協(xié)調(diào)機(jī)制，為著絲粒功能的可塑性提供新見解。
著絲粒是維持基因組穩(wěn)定的關(guān)鍵染色體區(qū)域，富含高度相似的重復(fù)序列，同時也是基因組結(jié)構(gòu)最復(fù)雜、變化最劇烈的區(qū)域，在進(jìn)化過程中產(chǎn)生復(fù)雜的遺傳多樣性。在大多數(shù)真核生物中，快速變異的著絲粒序列可以促進(jìn)核型進(jìn)化和新物種形成。盡管著絲粒存在高度異質(zhì)性，但尚不完全了解這些廣泛變異的序列是如何確保著絲粒功能的穩(wěn)健。小麥?zhǔn)堑湫偷漠愒戳扼w作物，包含3套高度相似又存在差異的亞基因組，著絲粒對多倍體基因組的穩(wěn)定尤為關(guān)鍵。
該研究以來自全球小麥育種計劃的10+品系群體為對象，系統(tǒng)解析了每個材料著絲粒的定位和序列組成。研究人員捕獲到小麥著絲粒重復(fù)序列、位置等存在大量變異，發(fā)現(xiàn)不同材料著絲粒存在廣泛的重定位現(xiàn)象。在不同材料中均發(fā)現(xiàn)與著絲粒重要表觀標(biāo)記CENH3核小體緊密結(jié)合的重復(fù)序列是逆轉(zhuǎn)錄轉(zhuǎn)座子Cereba，并且系統(tǒng)發(fā)育結(jié)果表明在不同小麥品系中Cereba轉(zhuǎn)座子序列表現(xiàn)出較為一致的同質(zhì)性，但結(jié)合程度較低的重復(fù)序列在每個小麥品系中表現(xiàn)出獨特性，這意味著存在特定機(jī)制選擇某些重復(fù)序列類型作為功能核心著絲粒的組成。此外，研究人員還觀察到CENH3核小體在復(fù)雜的著絲粒重復(fù)序列（包括重新定位的著絲粒）上顯示出較松散的DNA末端包裹，不同品系中嚴(yán)格的CENH3核小體占位和內(nèi)在DNA序列特征在確定著絲粒功能方面發(fā)揮關(guān)鍵作用。這些結(jié)果表明，多種機(jī)制參與小麥10+基因組材料CENH3核小體的適應(yīng)并穩(wěn)定著絲粒功能。最終，研究人員提出在不同的基因組背景下著絲粒染色質(zhì)具有明顯的表觀遺傳可塑性，并且由于過去的育種選擇，著絲粒的高穩(wěn)健性對于維持小麥基因組穩(wěn)定性至關(guān)重要。
我校植物科學(xué)技術(shù)學(xué)院碩士研究生馬桓和丁文濤為論文共同第一作者，小麥團(tuán)隊鄢文豪教授、茆海亮教授、蘭彩霞教授、李強(qiáng)教授和陳偉教授對該研究進(jìn)行了指導(dǎo)和建議。該研究得到國家重點研發(fā)計劃（2021YFF1000800）、國家自然科學(xué)基金（32170571）等項目資助。
蘇漢東課題組主要聚焦于小麥染色體生物學(xué)和合成基因組學(xué)的研究，探索小麥遠(yuǎn)緣雜交和多倍化的遺傳機(jī)制，并利用人工染色體進(jìn)行植物合成基因組學(xué)的探索。已在PNAS、Plant Cell、Genome Research、PLOS Biology、Molecular Biology and Evolution、Plant Biotechnology J、New Phytologist、Plant Journal、PLOS Genetics等領(lǐng)域內(nèi)知名學(xué)術(shù)期刊發(fā)表研究論文20多篇。
論文鏈接：https://academic.oup.com/mbe/advance-article/doi/10.1093/molbev/msad176/7237417
英文摘要：Centromeres are the chromosomal regions that play a crucial role in maintaining genomic stability. The underling highly repetitive DNA sequences can evolve quickly in most eukaryotes, and promote karyotype evolution. Despite their variability, it is not fully understood how these widely variable sequences ensure the homeostasis of centromere function. In this study, we investigated the genetics and epigenetics of centromeres in a population of wheat lines from global breeding programs. We captured a high degree of sequences, positioning, and epigenetic variations in the large and complex wheat centromeres. We found that the most CENH3-associated repeats are Cereba element of retrotransposons and exhibit phylogenetic homogenization across different wheat lines, but the less-associated repeat sequences diverge on their own way in each wheat line, implying specific mechanisms for selecting certain repeat types as functional core centromeres. Furthermore, we observed that CENH3 nucleosome structures display looser wrapping of DNA termini on complex centromeric repeats, including the repositioned centromeres. We also found that strict CENH3 nucleosome positioning and intrinsic DNA features play a role in determining centromere identity among different lines. Specific non-B form DNAs were substantially associated with CENH3 nucleosomes for the repositioned centromeres. These findings suggest that multiple mechanisms were involved in the adaptation of CENH3 nucleosomes that can stabilize centromeres. Ultimately, we proposed a remarkable epigenetic plasticity of centromere chromatin within the diverse genomic context, and the high robustness is crucial for maintaining centromere function and genome stability in wheat 10+ lines as a result of past breeding selections.
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