An iTRAQ-based quantitative proteomic analysis reveals the role of mitochondrial complex I subunits in S-type cytoplasmic male sterility of maize

Maize S-type cytoplasmic male sterility (CMS-S) arises from the activity of the mitochondrial gene orf355. This sterility can be counteracted by the nuclear fertility-restoring allele, Rf3. CMS-S occurs when bicellular pollen collapses following microspore mitosis. Despite this knowledge, the precise protein alterations in CMS-S mitochondria preceding pollen collapse are not well-understood. Our study compared the mitochondrial proteomic profiles between CMS-S and maintainer lines. We found that oxidative phosphorylation (OXPHOS) and glycolysis were significantly associated with CMS-S. A detailed analysis of the differentially abundant proteins (DAPs) associated with the OXPHOS pathway revealed that complex I (CI) subunits play a vital role in the degenerative process of maize CMS-S. Among these, the CI-B8 subunit exhibited abundant presence in CMS-S and displayed earlier transcriptional changes compared to other DAP genes. A yeast two-hybrid assay revealed a physical interaction between another DAP, the CI-13kDa subunit, and orf355 in yeast. These findings highlight the pivotal role played by complex I in the sterility mechanism of CMS-S in maize microspores.