Leymus chinensis (sheepgrass), a dominant perennial grass in the Eurasian Steppe, is well known for its adaptability and forage quality. Hardly any breeding has been done on it, limiting its potential in ecological restoration and forage productivity. To enable genetic improvement of the untapped, important species, we obtained a 7.85-Gb genome of L. chinensis with a particularly long contig N50 (318.49 Mb). Its allotetraploid genome is estimated to originate 5.29 million years ago from a cross between the Ns-subgenome relating to Psathyrostachys and the unknown Xm-subgenome. Multiple bursts of transposons after genome allo-polyploidization contributed to its genome expansion and complexity. With the genome resource available, we successfully developed a genetic transformation and gene-editing pipeline in L. chinensis. We knocked out miR528 using CRISPR/Cas9, resulting in the improvement of yield-related traits with increases in the tiller number and growth rate. Additionally, the morphological changes of L. chinensis were recorded in the natural environment throughout the year due to its ability to overwinter at extremely low temperatures. Transcriptome and DNA methylation pattern of L. chinensis under different seasons were drawn to understand genome wide genetic and epigenetic mechanism of its freezing-tolerance and to explore and provide gene resource for the improvement of cold tolerance of related species.
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 the wild grass.