Objective To reveal the molecular basis of rice seed maturation at the protein level, and explore the key proteins and metabolic pathways involved in regulating rice seed maturation.

Method The experiment used mature rice seeds at 30 days after pollination, and conducted mass spectrum identification using 4D label-free quantitative proteomics. Bioinformatics techniques were used to analyze the subcellular localization, domains, GO annotations, and KEGG pathway annotations of the proteins.

Result A total of 3 484 seed maturation proteins were identified, with most having a relative molecular mass between 10 000 and 100 000. They were mainly distributed in the cytoplasm, nucleus, chloroplasts, mitochondria, and plasma membrane. The protein domain mainly involved the RNA recognition motifs of protein translation and the protein kinase domains of protein phosphorylation modification. GO analysis showed that the proteins of mature seeds were mainly involved in cellular and metabolic processes, mainly related to catalytic activity and binding functions, and were mostly distributed in cell, cellular component, organelle, and cytomembrane. KEGG analysis revealed that proteins were mainly enriched in pathways such as ribosome, protein processing in endoplasmic reticulum, oxidative phosphorylation, and glycolysis. It was speculated that protein translation, processing, and energy metabolism were the main molecular events of rice seed maturation. Furthermore, proteins related to abscisic acid (ABA) signaling and indoleacetic acid (IAA) metabolism were identified, and transcription factors of the NAM, ATAF1/2 and CUC2 (NAC) family were also discovered.

Conclusion The accumulation of storage substances and energy metabolism are typical characteristics of rice seed maturation, and ABA and IAA signaling pathways are involved in the process of seed maturation.