Grass seeds play a critical and fundamental role in grass breeding and production. Elymus sibiricus L. is a widespread Poaceae forage grass in northern Eurasia which is used for ecological restoration and forage production. Sucrose is the main source of substrate and energy required for starch synthesis in the seeds, so the hydrolysis of sucrose determines and influences starch synthesis and filling in the seeds, especially Poaceae. However, the process behind carbohydrate metabolism during E. sibiricus seed development remains unclear. This study addresses a significant gap in our understanding of the carbohydrate metabolism during seed development in E. sibiricus by employing full-length transcriptome sequencing across five developmental stages for the first time. Full-length transcriptome sequencing was performed on E. sibiricus seeds at five developmental stages (S5, S9, S15, S20, S25) to get better molecular insights. We identified 13,205 differentially expressed genes, with 7,471 up-regulated and 5,734 down-regulated. Through KEGG enrichment analysis, genes were enriched in ‘starch and sucrose metabolism’, ‘photosynthetic-related’ and ‘hormone signal transduction’ pathways. Gene ontology enrichment analysis showed that genes were enriched in the ‘beta-amylase activity’ term of molecular functions. In addition, top 21 transcription factor families were identified as involved in seed development. The homologous genes of ABSCISIC ACID-INSENSITIVE 3 (ABI3), NUCLEAR FACTOR-YB1 (NF-YB1), STARCH SYNTHASE I (SSI) were identified as candidate genes of seed development in E. sibiricus. Combined with physiological index, transcriptome analyses, weighted gene co-expression network analysis and real-time quantitative PCR, the mechanism of starch and sucrose content of seed development was revealed and ten hub genes were identified. Overall, this study provides the molecular bases to understand seed development and starch and sucrose metabolism at the different seed developmental stages in E. sibiricus.

草种子在草的育种和生产中起着关键和基础性的作用。Elymus sibiricus L. 是欧亚大陆北部广泛分布的禾本科牧草，用于生态恢复和牧草生产。蔗糖是种子中淀粉合成所需的底物和能量的主要来源，因此蔗糖的水解决定并影响种子中淀粉的合成和填充，尤其是禾本科植物。然而，E. sibiricus 种子发育过程中碳水化合物代谢背后的过程仍不清楚。本研究首次在五个发育阶段采用全长转录组测序，解决了我们对 E. sibiricus 种子发育过程中碳水化合物代谢的理解中的重大差距。对 5 个发育阶段 （S5 、 S9 、 S15 、 S20 、 S25） 的 E. sibiricus 种子进行全长转录组测序，以获得更好的分子见解。我们鉴定了 13,205 个差异表达基因，其中 7,471 个上调，5,734 个下调。通过 KEGG 富集分析，基因富集在 '淀粉和蔗糖代谢' 、 '光合作用相关' 和 '激素信号转导' 途径中。基因本体富集分析表明，基因富集在分子功能的 “β-淀粉酶活性 ”项中。此外，前 21 个转录因子家族被确定为参与种子发育。脱落酸不敏感 3 （ABI3）、核因子-YB1 （NF-YB1）、淀粉合酶 I （SSI） 同源基因被鉴定为西伯利亚桉种子发育的候选基因。 结合生理指标、转录组分析、加权基因共表达网络分析和实时定量PCR，揭示了淀粉和蔗糖含量对种子发育的影响机制，并鉴定出10个枢纽基因。总体而言，本研究为了解西伯利亚桉不同种子发育阶段的种子发育以及淀粉和蔗糖代谢提供了分子基础。