BackgroundPopulus deltoidesis widely cultivated in China and produces a large number of pollen and poplar flocs from March to June per year. Previous studies have found that the pollen ofP. deltoidescontains allergens. However, studies on the ripening mechanism of pollen/poplar flocs and their common allergens are very limited.MethodsProteomics and metabolomics were used to study the changes of proteins and metabolites in pollen and poplar flocs ofP. deltoidesat different developmental stages. Allergenonline database was used to identify common allergens in pollen and poplar flocs at different developmental stages. Western blot (WB) was used to detect the biological activity of common allergens between mature pollen and poplar flocs.ResultsIn total, 1400 differently expressed proteins (DEPs) and 459 different metabolites (DMs) were identified from pollen and poplar flocs at different developmental stages. KEGG enrichment analysis showed that DEPs in pollen and poplar flocs were significantly enriched in ribosome and oxidative phosphorylation signaling pathways. The DMs in pollen are mainly involved in aminoacyl-tRNA biosynthesis and arginine biosynthesis, while the DMs in poplar flocs are mainly involved in glyoxylate and dicarboxylate metabolism. Additionally, 72 common allergens were identified in pollen and poplar flocs at different developmental stages. WB showed that there were distinct binding bands between 70 and 17KD at the two groups of allergens.ConclusionsA multitude of proteins and metabolites are closely related to the ripening of pollen and poplar flocs ofPopulus deltoides, and they contain common allergens between mature pollen and poplar flocs.