Abstract
Cabbage (Brassica oleracea L. var. capitata), an important vegetable crop in the Brassicaceae family, is economically important worldwide. In the process of hybrid seed production, Ogura cytoplasmic male sterility (OguCMS), controlled by the mitochondrial gene orf138, has been extensively used for cabbage hybrid production with complete and stable male sterility. To identify the critical genes and pathways involved in the sterility and to better understand the underlying molecular mechanisms, the anther of OguCMS line R2P2CMS and the fertile line R2P2 were used for RNA-seq and iTRAQ (Isobaric Tags for Relative and Absolute Quantitation) proteome analysis. RNA-seq analysis generated 13,037,109 to 13,066,594 SE50-clean reads, from the sterile and fertile lines, which were assembled into 36,890 unigenes. Among them, 1,323 differentially expressed genes (DEGs) were identified, consisting of 307 up- and 1016 down-regulated genes. For ITRAQ analysis, a total of 7,147 unique proteins were identified, and 833 were differentially expressed including 538 up- and 295 down-regulated proteins. These were mainly annotated to the ribosome, spliceosome and mRNA surveillance pathways. Combined transcriptomic and proteomic analyses identified 22 and 70 genes with the same and opposite expression profiles, respectively. Using KEGG analysis of DEGs, gibberellin mediated signaling pathways regulating tapetum programmed cell death and four different pathways involved in sporopollenin synthesis were identified. Secretion and translocation of the sporopollenin precursors were identified, and the key genes participating in these pathways were all significantly down-regulated in R2P2CMS. Light and transmission electron (TE) microscopy revealed fat abnormal tapetum rather than vacuolization and degradation at the tetrad and microspore stages of the OguCMS line. This resulted in the failed deposition of sporopollenin on the pollen resulting in sterility. This study provides a comprehensive understanding of the mechanism underlying OguCMS in cabbage.
Highlights
Cabbage (Brassica oleracea var. capitata) is the most widely grown vegetable crop in the world
By combining transcriptome and proteome, we identified key genes and pathways which may participate in tapetum programmed cell death (PCD) and sporopollenin synthesis for pollen wall development in Transcriptome and proteome analysis of Ogura cytoplasmic male sterility (OguCMS) cabbage cabbage
Tapetum PCD at the tetrad stage is regulated by the GA mediated signaling pathway, in which differentially expressed genes (DEGs) such as GA-regulated family proteins, PLP4, and transcription factors like TDF1, bHLH type-AMS, MYB were suppressed in R2P2CMS
Summary
Cabbage (Brassica oleracea var. capitata) is the most widely grown vegetable crop in the world. The Ogura cytoplasmic male sterility (OguCMS) system, which is controlled by the mitochondrial gene orf138, is becoming the most common method of cabbage F1 hybrid production [1]. As cytoplasmic male sterile lines and maintainer lines have the same nuclear genome, OguCMS is an important tool for genetic improvement and utilization of heterosis in crops, and a classic model to explore cytoplasm mechanism and reverse signaling pathways in pollen development biology [2,3]. Despite the non-homologous sequence between orf138 and other CMS genes, the genes share common traits. They derive from high rearrangement of the mitochondrial genome, are co-transcribed with ATPase, and encode a small protein with hydrophobic areas. While for orf138 in OguCMS, the spontaneous promotion of the absence of fertility occurred instead of combining to the respiratory complex
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