Comparative proteomic analysis of the H99 inbred maize (Zea mays L.) line in embryogenic and non-embryogenic callus during somatic embryogenesis

A proteomic approach based on two-dimensional electrophoresis (2-DE) and mass spectrometry was performed to investigate somatic embryogenesis in the H99 inbred maize line by comparing embryogenic and non-embryogenic callus. Protein spots (n = 42) were differentially expressed between embryogenic calli and non-embryogenic calli according to our image analysis. Among them, 33 proteins were differentially expressed by at least threefold, with 15 up-regulated and 18 down-regulated in the embryogenic callus versus the non-embryogenic callus. However, only nine proteins were expressed in either of the calli. Twenty-nine protein spots were identified using mass spectrometry analysis and classified into several categories based on the matrix-science MASCOT and NCBI databases. These categories included cell proliferation (10.34 %), transcription and protein processing (17.24 %), stress response (10.34 %), signal transduction (3.45 %), metabolism and energy (48.28 %) and hypothetical function (10.34 %). Their putative roles are discussed according to their relevance in somatic embryogenesis. Real-time reverse transcription polymerase chain reaction analysis revealed that the expression levels of five selected genes were consistent with the profiles detected in the 2-DE gels, further confirming the proteomic analysis. This study is the first comparative proteome analysis between the embryogenic callus and the non-embryogenic callus of the H99 inbred line. Our results show the differentially expressed proteins between the two callus types and reveal some key proteins that may have significant roles in molecular events during somatic embryogenesis in this species.