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Analysis of Differential Expression of Mitochondrial Proteins between C-Type Cytoplasmic Male Sterility Line C48-2 and Maintainer in Maize

Cytoplasmic male sterility (CMS) in maize (Zea mays L.) is categorized into T-CMS, C-CMS, and S-CMS types based on the specific restoration of nuclear gene, in which C-CMS has a great application potential in maize hybrid breeding due to its stable sterility and resistance to Helminthosporium maydis Nisik. The sterile mechanism of C-CMS is not fully understood for its later discovery and utilization than these of T-CMS and S-CMS. The objective of the study was to give some evidences and explanations to the sterility reason of C-CMS in maize by analyzing the differential expression of anther mitochondrial proteome between a C-type sterile line (C48-2) and its maintainer (N48-2). The mitochondrial proteins in anthers of C48-2 and N48-2 were separated firstly by two-dimensional electrophoresis with immobilized pI (310, non-linear) gradients and then by SDS-PAGE. The coomassie brilliant blue-stained protein spots were analyzed using PDQUEST software, there were about 260 detectable spots on each 2D-gel. With direct MALDI-TOF mass spectrometry analysis and protein database searching, only 2 out of 10 protein spots were identified with significative data, which were up-regulated in mononuclear phase of C48-2. They were identified as glutamate dehydrogenase (GDH) and voltage-dependent anion channel protein-1 (VDAC1), respectively. The GDH exists mainly in mitochondria of higher plants and plays an important role in nitrogen metabolism. Once the GDH is up-regulated at any phase of plant development, the normal supply of energy will be affected, probably leading to cytoplasmic sterility. The VDAC1 plays an essential role not only in the permeability of the mitochondrial membrane, but also in apoptosis mediated by the mitochondrial pathway. Overexpression of VDAC1 in a variety of cells induced apoptotic cell death, indicating VDAC1 as a conserved mitochondrial element of the death machinery. Our research suggests that the GDH and VDAC1 in mitochondria probably cause the sterility in C-CMS in maize.