Proteomic Analysis of Tropical Maize Inbred Line QR273 at Different Growth Stages Under Long-Day Conditions

Tropical maize often exhibits photoperiod sensitivity, which limits its adaptation to temperate regions. Understanding its proteomic dynamics under long-day conditions is therefore crucial for germplasm improvement. This study employed a Tandem Mass Tag (TMT)-based proteomic approach to investigate stage-specific protein expression patterns in the tropical maize inbred line QR273 under long-day conditions (16 h light/8 h dark). Seeds were cultivated in climate chambers, and leaves were collected at the four-leaf (P4) and nine-leaf (P9) stages. A total of 2881 differentially expressed proteins (DEPs) were quantified between the P4 and P9 stages, among which only 7 were upregulated and 2874 were downregulated at the P9 stage. Gene Ontology (GO) enrichment analysis revealed that these DEPs were significantly enriched in processes related to proteolysis, membrane components, and ATP binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed the enrichment of DEPs in amino acid biosynthesis, secondary metabolite biosynthesis, and aminoacyl-tRNA biosynthesis pathways. Protein–protein interaction (PPI) network analysis identified 60S ribosomal protein L12, adenosine 5′-phosphosulfate reductase, and RuvB helicase as core hub proteins. Based on functional annotation of representative DEPs, the DEPs were classified into four categories: 9 proteins related to storage material protection, 14 proteins related to protein modification, 12 proteins related to photosynthesis, and 25 proteins with other biological functions. Comparative analysis demonstrated a decrease in storage material protection, protein modification, and photosynthetic capacity at the P9 stage relative to the P4 stage. These findings provide insights into the proteomic dynamics underlying tropical maize development under long-day conditions and offer a theoretical basis for genetic improvement of tropical maize germplasm. Notably, inferences regarding nutrient reallocation based on DEP downregulation are derived solely from proteomic data and require further experimental validation.