Identification of differentially expressed genes in soybean seeds differing in oil content

Characterization of gene regulation is fundamental for achieving an understanding of the complex processes for oil synthesis. Up to now, it is still unknown how many genes are involved in the oil synthesis in soybean ( Glycine max L.) seeds. In this study, we examined the gene expression of different seed maturity using two contrasting cultivars (Zhongdou 32, a high-oil cultivar and Youchun 02–6, a low-oil cultivar). Results indicated that seed oil content varied with maturing stages. Two significant increases of oil content were observed at 22 and 43 days after flower (DAF) in Zhongdou 32. To explore their molecular basis, differentially expressed gene clones in two soybean cultivars and two development stages were analyzed by SSH. All SSH clones were arrayed and screened by dot-blotting hybridization, followed by semi-quantitative PCR analysis for selected clones, and finally determined by real-time quantitative RT-PCR. A total of 59 genes have been examined successfully in two cultivars. At 36 DAF, 33 genes were found with high expression in Zhongdou 32, while the other 26 genes in Youchun 02–6. In Zhongdou 32, a total of 33 genes showed differential expression at 15 and 36 DAF. 13 genes showed a high expression at 15 DAF, while the other 20 genes at 36 DAF. A homology search for their nucleotide sequences revealed that the above genes are highly homologous to known sequences of genes for oil biosynthesis, energy metabolism, signal transduction, and stress response, and some genes have not been implicated previously in oil synthesis. Tissue-specific analysis indicated that most of genes expressed in seed, and 10 genes expressed specifically in seeds. Time-course analysis of transcript accumulation indicated that the expression of seed-specific genes changed with development stages, which were probably associated with oil biosynthesis. The results provide information on gene-encoding factors responsible for oil synthesis. Functional studies of the seed-specific genes would shed new light on both the molecular basis of oil metabolism and the regulatory pathways.