Application of somatic embryos to rapid and reliable analysis of soybean seed components by RNA interference-mediated gene silencing

Soybean somatic embryos have attracted attention both as a model of zygotic embryos and as explants for the generation of transgenic plants. beta-Conglycinin, which is composed of three subunits (alpha, alpha', and beta) that are encoded by a multigene family, is a major seed component of soybean, and accumulates in somatic embryos with their maturation. We subjected the somatic embryos to transformation with vectors encoding double-stranded RNA fragments of various sizes that correspond to the gene for the alpha' subunit of beta-conglycinin. These DNA fragments were put under the control of the promoter region of the gene for another major seed protein, the A2B1a subunit of glycinin. Transgenic somatic embryos were obtained within 2 months of transformation, and the resulting mature embryos manifested down-regulation of the alpha' subunit of beta-conglycinin in a manner dependent on the size of the RNAi vector insert. Accumulation of small interfering RNA and depletion of mRNA corresponding to the alpha' subunit were indicative of RNAi. The amounts of alpha and beta subunits of beta-conglycinin, which share high sequence similarity with the alpha' subunit, were also reduced in the mature somatic embryos. Moreover, the abundance of all beta-conglycinin subunits was greatly reduced in the seeds of regenerated transgenic plants. Our results indicate that the application of RNAi to somatic embryos is a feasible and rapid option for functional studies of soybean seed components.