Abstract
Triploid poplar trees have been shown to have a number of growth advantages, especially much bigger leaves that contribute greatly to the increased biomass. In this study, we focused on the relationships between leaf age and leaf metabolism in triploids. We performed comparative proteomic analysis of the 5th (FDR5), 10th (FDR10), and 25th (FDR25) leaves from the apical meristems in allotriploids originated from first-division restitution (FDR). A total of 1970, 1916, and 1850 proteins were identified in the FDR5, FDR10, and FDR25, respectively. Principle component analysis (PCA) and differentially accumulated protein (DAP) analysis showed that FDR10 and FDR25 displayed higher similarities of protein accumulation patterns as compared to FDR5. MapMan enrichment analysis showed that several primary metabolic pathways or processes were significantly enriched in the DAPs. For example, photosynthesis, major CHO metabolism, glycolysis, N metabolism, redox, C1-metabolism, DNA, and protein turnover were significantly altered in both FDR10 and FDR25 compared with FDR5. In addition, amino acid metabolism and gluconeogenesis/glyoxylate cycle also underwent significant changes in FDR25 compared with FDR5. However, only amino acid metabolism was significantly enriched in the DAPs between FDR25 and FDR10. Further, DAP accumulation pattern analysis implied that FDR5, FDR10, and FDR25 were placed in the young, mature, and primary senescence stages of leaves. The most DAPs involved in the light reaction, photorespiration, Calvin cycle, starch and sucrose metabolism, pentose phosphate pathway (OPP), tricarboxylic acid (TCA) cycle, N metabolism, and C1-metabolism displayed higher accumulation in both FDR10 and FDR25 compared to FDR5. However, the most DAPs that are involved in cell wall and lipid metabolism, tetrapyrrole synthesis, nucleotide metabolism exhibited lower accumulation in both FDR10 and FDR25. Almost all DAPs between FDR-10 and FDR-25 showed a dramatic decrease in FDR25. KEGG enrichment analysis showed that carbon metabolism was altered significantly at different leaf ages. DAPs that are involved in carbon metabolism were predicted as different points in protein–protein interaction (PPI) networks from the STRING database. Finally, inconsistent transcript and protein abundance was found for DAPs, indicating the presence of posttranscriptional regulation during leaf-age progression process.
Highlights
The results showed that most differentially accumulated protein (DAP) involved in the light reaction, photorespiration, Calvin cycle, starch and sucrose metabolism, pentose phosphate pathway (OPP), tricarboxylic acid (TCA) cycle, N metabolism, and C1-metabolism displayed higher abundance in both FDR10 and FDR25 than those in FDR5 (Figure 3a,b), suggesting that FDR10 and FDR25 promoted the growth of poplars through vigorous carbohydrate synthesis and catabolism
1970, 1916, and 1850 proteins were detected in FDR5, FDR10, and FDR25, respectively
Comparative proteomic analysis revealed that FDR5, FDR10, and FDR25 represented three different age stages of leaves, namely young, mature, and primary senescence
Summary
Proteomics has contributed greatly to our understanding of information on protein accumulation.In plants, proteomics has been applied to protein quantitative profiling [1], post-translational modifications [2], signaling pathway recognition [3], subcellular localization, and interactions [4,5].Many biological processes, including biotic and abiotic stress [6,7], development [8], nutrient sensing, and polyploidization [9,10], have been characterized by using proteomics.Populus has long been an important model system for studies of forest tree species because of the available genetic and genomic resources, small genome size, and fast growth speed [11]. Proteomics has contributed greatly to our understanding of information on protein accumulation. Kalluriet et al reported shotgun MS/MS profiling to the proteome of Populus developing xylem, identifying nearly 6000 proteins [13]. Hurst et al investigated the proteome of fully expanded leaves from greenhouse-grown Populus trees using a shotgun mass spectrometry-based proteomics method, detecting over 2500 proteins [14]. Liu et al presented a proteome profiling of Populus early stem from primary to secondary growth using two-dimensional gel electrophoresis (2-DE) followed by LC-ESI-Q-TOF-MS, identifying 165 differential abundant proteins during various growth stages of Populus early stems [15]. Wang et al analyzed the mature Populus pollen proteome, identifying 159 distinct proteins from 242 spots analyzed by 2-DE and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF/TOF MS) [16].
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