Transcriptome analyses of embryos at two developmental stages reveals important insights into oil body development and lipid accumulation in radish ( Raphanus sativus L.)

Radish is used widely as a root vegetable and is also suitable for production of edible oil. However, the mechanism of development of the oil body and the accumulation of oil in the seeds of radish have rarely been studied. In this study, we used ultrastructural analyses to trace the formation of the oil body during embryo development in radish. We found that peripheral cells around the globular embryo began to differentiate and the oil body started to appear at the bent-embryo stage. A robust increase in oil bodies was found at the mature cotyledon stage. Thus, embryos at the bent-embryo and mature-cotyledon stages were selected for transcriptome analyses to uncover the regulation of oil accumulation. In total, 16,444 unigenes with an average length of 805 bp and an N50 of 1,390 bp were obtained from the two different embryos of radish after de novo sequencing. The KEGG(Kyoto Encyclopedia of Genes and Genomes) classification of unigenes assigned 12,412 unigenes to 43 functional categories. Comprehensive analyses showed that there were 2,528 upregulated and 3,164 downregulated differentially expressed genes. Those related to lipid metabolism were found in the fatty acid synthesis and degradation pathway and validated by qPCR. The results identified candidate genes potentially involved in oil biosynthesis, which may be useful for revealing the accumulation process of oil in radish.