Proteomics variations after short-term heat shock treatment reveal differentially expressed proteins involved in early microspore embryogenesis in cabbage (Brassica oleracea)

Abstract

Background Microspore embryogenesis (ME) provides an efficient way to breed crops. In many cases, short-term heat shock treatment can greatly increase the embryogenesis rate of brassicas. However, its molecular mechanism is largely unclear. Results To mine for the key genes, pathways and interplay in the underlying networks, we compared the proteomes of isolated microspores with samples pre-treated at 32 °C for 24 h and 25 °C for 24 h using two cabbage accessions (Zhonggan 628 and 87-534) showing extremely different embryogenic rates. The embryo yield was 0 and 19.7 embryos/bud for Zhonggan 628 at 25 °C and 32 °C, respectively, and was 0 for 87-534 at both temperatures. Using a label-free proteomics technology, more differentially expressed proteins (DEPs) were found for Zhonggan 628 (363 DEPs, 115 upregulated and 248 downregulated) than for 87-534 (282 DEPs, 162 upregulated and 120 downregulated). 97 DEPs specially identified only in Zhonggan 628 but not in 87-534 after heat-shock treatment were the key proteins that maybe related to heat shock-induced embryogenesis in vitro culture. Those 97 DEPs were mainly enriched in carbon metabolic process and protein synthesis and degradation process. Malate dehydrogenase (mMDH), sgt1 homolog B (SGT1), heat shock 70 kDa protein 5 (HSP70), and cell division control protein 48 homolog A (CDC48) may play an important role in cabbage embryogenesis and were identified based on pathway enrichment and protein−protein interaction analyses. In addition, changes in the abundance of 9 representative DEPs were correlated with their corresponding mRNA levels using qRT-PCR. Carbohydrate metabolism supplies the energy needed for the rapid growth that occurs during embryo development, and the folding of synthesized proteins or the refolding of damaged and unstable proteins occur, which may due to the stress induced by in vitro culture. Conclusions A set of putative proteins presumably specific for microspore embryogenesis induced by high temperature treatment were identified. In isolated microspore culture of cabbage, we present the first exposition of non-embryo and the embryo (induced by 32 °C heat shock treatment 24h) changes in the expression of specific proteins.