Transcriptomic Dynamics Associated with the Seed Germination Process of the Invasive Weed Cenchrus longispinus

Sandbur [Cenchrus longispinus (Hack.) Fernald] is a major invasive weed in the agro-pastoral ecotone of northern China. It propagates via seeds encased in spiny burs. Each bur encloses a pair of seeds, and the larger M-type seeds germinate first, functioning as pioneer plants, while smaller P-type seeds remain dormant. Thus, the rapid germination of M-type seeds is pivotal for population sustenance. In this study, we investigated the transcription response involved in the germination of C. longispinusus M-type seeds during four stages (drying, imbibition, exposure, and sprouting). A total of 24,399 DEGs were identified by comparing two consecutive germination stages, with most DEGs found in the imbibition stage. GO enrichment analysis showed that the DEGs were mainly enriched in substance metabolic and regulatory processes. Correspondingly, KEGG enrichment analysis indicated that the functions of DEGs were significantly concentrated in secondary metabolite synthesis pathways, as well as substance and energy metabolic pathways. Notably, the expression of starch-and-sugar metabolism-related genes increased as germination progressed. Additionally, ABA synthesis-related genes were notably downregulated, while those regulating ABA catabolism were significantly upregulated. Moreover, GA synthesis-related genes were activated, especially in the imbibition stage, with nine GA20ox genes highly expressed. These research findings help us gain a deeper understanding of the seed germination mechanism of C. longispinus.