Analysis of differentially expressed genes during embryogenesis in ovary culture of cucumber (Cucumis sativus L.)
Abstract Background: Ovary culture has been a useful way to generate double haploid (DH) plant in cucumber (Cucumis sativus L.). However, the rate of embryo induction is low, and the probability for the induced embryo to grow into normal embryo is low as well. This is largely due to unknown of the mechanism of embryogenesis in cucumber. In this study, the differentially expressed genes during embryogenesis, including the early stages of embryo formation, embryo maturation and shoot formation, was investigated with transcriptomic technique to set up basis for a more efficient ovary culture technology Results: Cytological observations led to suggestions that cell enlargement is the symbol that gametophytes had switched to the sporophyte development pathway during the early embryogenesis stage. In this stage, RNA-seq revealed 3468 up-regulated genes, including hormone signal transduction genes, hormone response genes and stress-induced genes. The reported embryogenesis-related genes BBM, HSP90 and AGL were also actively expressed during this stage. The total of 480 genes that function in protein complex binding, microtubule binding, tetrapyrrole binding, tubulin binding and other microtubule activities were continuously up-regulated during the embryo maturation stage, indicating that the cytoskeleton structure was continuously being built and maintained by the action of microtubule-binding proteins and enzyme modification during embryo development. In the shoot formation stage, 1383 genes were up-regulated, which were mainly enriched in phenylpropanoid biosynthesis, plant hormone signal transduction, phenylalanine metabolism, and starch and sucrose metabolism. The shoot formation stage might be regulated by 6 transcription factors that contained a B3 domain, 9 genes in the AP2/ERF family and 2 genes encoded WUS homologous domain proteins. Conclusions: Findings from this study offer a valuable framework for explaining the transcriptional regulatory mechanism underlying embryogenesis in cucumber ovary culture.