Proteomic changes in maize as a response to heavy metal (lead) stress revealed by iTRAQ quantitative proteomics

Lead (Pb), a heavy metal, has become a crucial pollutant in soil and water, causing not only permanent and irreversible health problems, but also substantial reduction in crop yields. In this study, we conducted proteome analysis of the roots of the non-hyperaccumulator inbred maize line 9782 at four developmental stages (0, 12, 24, and 48 h) under Pb pollution using isobaric tags for relative and absolute quantification technology. A total of 252, 72 and 116 proteins were differentially expressed between M12 (after 12-h Pb treatment) and CK (water-mocked treatment), M24 (after 24-h Pb treatment) and CK, and M48 (after 48-h Pb treatment) and CK, respectively. In addition, 14 differentially expressed proteins were common within each comparison group. Moreover, Cluster of Orthologous Groups enrichment analysis revealed predominance of the proteins involved in posttranslational modification, protein turnover, and chaperones. Additionally, the changes in protein profiles showed a lower concordance with corresponding alterations in transcript levels, indicating important roles for transcriptional and posttranscriptional regulation in the response of maize roots to Pb pollution. Furthermore, enriched functional categories between the successive comparisons showed that the proteins in functional categories of stress, redox, signaling, and transport were highly up-regulated, while those in the functional categories of nucleotide metabolism, amino acid metabolism, RNA, and protein metabolism were down-regulated. This information will help in furthering our understanding of the detailed mechanisms of plant responses to heavy metal stress by combining protein and mRNA profiles.