Global expression profiles and targeted pathway modulation during soybean embryo development

The molecular events underlying plant embryo development are poorly known. A global approach (microarray analysis) was used to identify genes differentially expressed during the development of somatic embryogenesis and a targeted approach (transformation) was used to specifically examine the effect of modulating chalcone synthase (CHS) expression in soybean seeds on isoflavone content.; Somatic embryos develop from the adaxial side of the cotyledon, while the abaxial side evolves into a callus. Using a 9,280-cDNA clone array, steady-state RNA from the adaxial side from which embryos develop and from the abaxial callus at five time points were compared over the course of the four weeks necessary for the development of globular embryos. The expression of each clone was profiled in the adaxial side during the same period. A total of 495 genes differentially expressed in at least one of these experiments were grouped according to the similarity of their expression profiles. Results indicate that the appearance of somatic embryos is preceded by dedifferentiation of the cotyledon during the first two weeks on auxin. Changes in mRNA abundance of genes characteristic of oxidative stress as well as genes indicative of cell division in the adaxial side of the cotyledons suggest that the arrangement of the new cells into organized structures might depend on a genetically controlled balance between cell proliferation and cell death. The data also suggest that the formation of somatic globular embryos is accompanied by the transcription of storage proteins and the synthesis of gibberellic acid.; In the second approach, five CHS transgenic soybean lines were generated. Relative mRNA abundance of transgenic and endogenous CHS genes was measured by real-time PCR. Three lines showed low transgene expression but increased transcript abundance for two endogenous CHS genes One line showed a 10-fold increase in CHS expression over the control seeds, but no change in isoflavone content, and is a candidate for more extensive profiling of flavonoid compounds.