Leymus chinensis is a dominant perennial herb in the Eurasian steppe, known for its remarkable adaptability and feed quality. Despite the growing recognition of its ecological and economic value, the loss of genome sequences and the challenges of their genetic transformation limit their critical applications in basic research and wild plant improvement. Published in PNAS (if=11.) on October 24, 20231) The article "Genome evolution and initial breeding of the triticeae grass leymus chinensis dominating the eurasian steppe", which examines the untapped genome sequence and genetic breeding of L. chinensis, reveals the heteropolyploidization and genomic evolution of this species.
Overview of the technical approach
In this study, we collected wild L. chinensis from the grassland of L. chinensis in Northeast China, and selected individual plants with strong rhizomes (LC6-5) for genome assembly based on Illumina, PacBio and HIC technologies, and comparative genome analysis was performed. 
Key results
1. L. chinensis genome assembly and annotation
In this study, the genome assembly of LC6-5 in a single plant was performed with a genome size of approximately 785GB, N50 is 31849 MB, BSUCO assessment completeness of 985% (Table 1). The repetitive sequence amounted to 689 GB, which is 87 of the entire genome76%, long-terminal repeat retro-transposons (LTR retro-transposons) constitute the most abundant repeat class, accounting for 7065%。Table 1Assembly and annotation of the L. chinensis genome
Fig.1 Gene profile of L. chinensis
2. Genomic subtypes and comparative genomic analysis of L. chinensis
In this study, the genome of L. chinensis was further haplotyped and divided into two subgenomes, NS subgenome and XM subgenome (Fig. 1D). Phylogenetic and molecular dating studies have shown that the NS subgenome and XM subgenome are in the region of about 1679 mya pre-differentiation (Figure 2A) and in approx. 4Polyploidization occurred before 18 MYA, resulting in the formation of heterotetraploid L. chinensis (Figure 2A). Collineearity analysis showed that the NS subgenome and XM subgenome were translocated on chromosome 4 and chromosome 5, and further collinearity analysis with other wheat species confirmed that the translocation of the L. chinensis genome occurred in the NS subgenome. In addition, the NS subgenome has a higher gene density and Te content as well as an evolutionary rate than the XM subgenome (Fig. 2E-G). 
FigGenomic evolution and tetraploid events of L. chinensis
3. Transposons are involved in genome evolution
LTR-retrotransposons (mainly gypsy and copia) were the most abundant transposons in the genome of L. chinensis, and the last three LTR insertions were identified, and the Gypsy insertions were 043 MYA and 151–1.84 mA was bimodal with Copia insertion at 065-0.72 MYAs have a unimodal distribution (Figure 3C) and are present in both subgenomes. This study further analyzes the intact LTR-RTS, which aims to organize, associate the different families of COPIA and Gypsy, and their roles in the two subgenomes. According to the reverse transcriptase domain-based phylogenetic tree (Figure 3D), COPIA and GYPSY belong to two separate superfamilies, with GYPSY containing six major clades and COPIA having eight clades, respectively. In addition, in a comparison of subgenomes, the authors found that the distribution patterns of the families were similar between NS and XM (Figure 3E), which provided an explanation for their similar genome size (3,998 MB for NS and 3,715 MB for XM). 
FigSheep grassAmplification and evolutionary analysis of LTR retrotransposons in the genome
4. Use genome editing system to induce gene modification of L. chinensis genome
This study established a study for LIn the genetic transformation system of chinensis, immature panicles were selected as transformation materials. By lThe leaves, roots, rhizomes, and spikelets of chinensis were sequenced by small RNAs, and a total of 393 mature miRNAs were identified. Of these, 38 miRNA families are conserved in the plant genome of Mirbase, while 13 families are specific to monocots (Figure 4B). In lAmong the monocotle-endemic miRNAs of chinensis, miR528 was most expressed in leaves (Fig. 4C), suggesting that it may have an important role in this species. The researchers also applied CRISPR Cas9 technology to successfully obtain two knockout mutants of MIR528. Transcriptome analysis of 35 potential target genes of miR528 was carried out, and the results confirmed the effect of miR528 on LThe tillering of chinensis has a negative regulatory effect.
FigInduced using a genome editing systemLeymus chinensis genomegenetic modifications
Summary
In conclusion, this study provides valuable genomic resources for the evolutionary study of wheat plants, and proposes a conceptual framework for using genomic information and genome editing to accelerate the improvement of wild L. chinensis with polyploidy and self-incompatibility characteristics.
References. genome evolution and initial breeding of the triticeae grass leymus chinensis dominating the eurasian steppe. pnas, 2023.