Elytrigia elongata （Host） Nevski， a perennial bunchgrass， possesses outstanding stress tolerance and forage quality. This study aimed to examine the chromosome number， karyotype composition， and gene expression profiles across various ploidy levels within E. elongata germplasm. Three accessions， designated EE030， EE031， and Ae4x， were used as experimental materials. Karyotype analysis was conducted via an enzymatic maceration method， and differences in gene expression among accessions with varying ploidy levels were analyzed through full-length transcriptome sequencing on the PacBio platform. The results revealed that accession EE031 is a diploid （2n=2x=14） with a karyotype formula of K（2n）=2x=10m+4sm， classified as the “1A” type. Accession Ae4x is identified as a tetraploid （2n=4x=28） with a karyotype formula of K（2n）=4x=20m+6sm+2st， classified as the “2A” type. Accession EE030 is a decaploid （2n=10x=70） with a karyotype formula of K（2n）=10x=56m+12sm+2st， also categorized as the “2A” type. In parallel， transcriptome analysis revealed that increased ploidy level was associated with an essential expansion in transcript abundance and functional diversity. Differentially expressed genes in EE031， Ae4x， and EE030 were enriched in 10， 12， and 15 KEGG metabolic pathways， as well as in 39， 38， and 64 GO functional terms， respectively. Furthermore， core functional pathways specific to each ploidy level were identified： （1） EE031 （diploid） was enriched in proteins related to Chromosomes and Chromosome-binding， Stress response， and Signal receptor activity； （2） Ae4x （tetraploid） was enriched in Transporter and Hydrolase activities； （3） EE030 （decaploid） was associated with Metabolism， Transporter， and Transferase activities.

Elytrigia elongata  /  Polyploidy  /  Karyotype analysis  /  Full-length transcriptome sequencing  /  Differentially expressed genes