Abstract: 【Objective】 Unintended effects of genetically modified (GM) crops are defined as the unexpected trait changes in GM breeding and research. Over the last decade, much attention has been taken to GM crops’ intended effects that are attributed to the insertion of foreign gene, leaving the unintended effects of GM crops less investigated. In this study, a comparative proteomic study using two-dimensional electrophoresis and mass spectrometry was conducted to assess the high-abundant protein variation, so as to explore possible occurrence of their unintended effects. 【Method】 Four insect resistant GM maize varieties, i.e SK12-5zd, IE034z, Bt799z and Bt799zd, which were under approval of GM safety assessment by the Ministry of Agriculture, were planted in a condition-controlled greenhouse together with their corresponding CKs, i.e Zheng58 and Zhengdan958. When seedling growing into 5-leaf stage, the top-leaf blades of each maize variety were sampled and their leaf proteins were extracted. After profiling by two-dimensional electrophoresis, on-gel leaf protein spots of each GM maize were compared against their corresponding CKs using Imager Scanner and PD Quest 8.0 (Biored, USA). The resulted unique and differential protein (with a relative volume greater than 2-fold) spots were isolated from the gel and applied for protein identification by mass spectrometry against the relevant protein database. The identified proteins were analyzed in gene ontology (GO) and KEGG for their cellular functionalities and metabolism pathway enrichment. 【Result】 Through comparison of the unique and differential proteins between each GM maize and its corresponding no-GM CKs among 4 insect resistant GM maize varieties, a total of 61 differential proteins were identified in maize PDB (NCBI) alongside the 4 intended insect resistant gene products. The gene ontology analyses of the identified proteins revealed that they are popular cellular enzymes of fundamental metabolism, i.e Rubisco, ATP synthase, pyruvate orthophosphate dikinase, etc. Only a few genes relating to photosynthesis, ATP synthesis and carbon fixation were observed to be up-expressed, possibly due to the genetic background difference between the GM maize and its CK. KEGG analyses uncovered that, in comparison with the corresponding CKs, the differential proteins of SK12-5zd and Bt799zd were enriched similarly into photosynthesis, carbon fixation and metabolism pathways. In comparison with the CK Z58, the differential proteins of both IE034z and Bt799z were enriched into the photosynthetic metabolism pathway. Four GM maize varieties exhibited extensive similarity over their corresponding wild-type controls. It appeared to be no unintended effects observed. 【Conclusion】 The preliminary results revealed no obvious unintended effects in 4 insect resistant GM maize varieties in respect to high-abundant proteomic assessment.

Key words: genetically modified maize, proteomics, unintended effects, two-dimensional electrophoresis (2-DE), differentially expressed protein