Genome of <i>L. chinensis</i>

<i>Leymus chinensis</i>, a dominant perennial grass in the Eurasian Steppe, is well known for its remarkable adaptability and forage quality. Hardly any breeding has been done on the grass, limiting its potential in ecological restoration and forage productivity. To enable genetic improvement of the untapped, important species, we obtained a 7.85-Gb high quality genome of <i>L. chinensis </i>with a particularly long contig N50 (318.49 Mb). Its allotetraploid genome is estimated to originate 5.29 million years ago (MYA) from a cross between the Ns-subgenome relating to <i>Psathyrostachys</i>, and the unknown Xm-subgenome. Multiple bursts of transposons during 0.433–1.842 MYA after genome allopolyploidization, which involved predominantly the Tekay and Angela of LTR retrotransposons, contributed to its genome expansion and complexity. With the genome resource available, we successfully developed a genetic transformation system as well as the gene editing pipeline in <i>L. chinensis</i>. We knocked out the monocot-specific miR528 using CRISPR/Cas9, resulting in the improvement of yield-related traits with increases in the tiller number and growth rate. Our research provides valuable genomic resources for Triticeae evolutionary studies and presents a conceptual framework illustrating the utilization of genomic information and genome editing to accelerate the improvement of wild <i>L. chinensis</i>, with features such as polyploidization and self-incompatibility.羊草（Leymus chinensis）是欧亚草原的优势多年生禾草，以卓越的适应性与优良的饲用品质广受认可。目前针对该草种的育种工作几乎处于空白状态，这极大限制了其在生态修复与饲草生产中的应用潜力。为实现这一未被充分开发的重要物种的遗传改良，我们成功获取了长度为7.85 Gb的高质量羊草基因组，其重叠群N50（contig N50）高达318.49 Mb，表现优异。 该异源四倍体基因组的起源可追溯至约529万年前（MYA），由与新麦草属（Psathyrostachys）相关的Ns亚基因组与未知的Xm亚基因组杂交演化而来。在基因组异源多倍化完成后，于0.433–1.842 MYA期间发生了多轮转座子爆发事件，其中以Tekay与Angela类长末端重复序列反转录转座子（LTR retrotransposons）占主导，这些事件共同推动了该基因组的扩张与复杂度提升。 依托这一基因组资源，我们成功建立了羊草的遗传转化体系与基因编辑流程。我们利用CRISPR/Cas9技术敲除了单子叶植物特有的miR528，最终获得了分蘖数增加、生长速率提升的产量相关性状改良株系。 本研究为小麦族（Triticeae）的进化研究提供了宝贵的基因组资源，并提出了一套理论框架，阐明了如何通过基因组信息与基因编辑技术，加速兼具多倍化与自交不亲和特性的野生羊草的遗传改良进程。