Alteration Of The Soybean Seed Proteome Results In Non-Seed Phenotypes and Enhanced Genome Methylation

Soybean (Glycine max L.) has numerous uses that largely revolve around its high oil and protein content.  We are interested in how the seed content is determined and, in particular, if the content can be altered for specific end uses.  We have engineered soybean via RNAi technology to have a seed-specific suppression of both its storage proteins (RNAiSP), glycinin and beta-conglycinin.  Together these proteins constitute over 80% of soybean’s near 40% seed protein content.  The resultant transgenic plants are phenotypically comparable to the nontransgenic counterparts and the seed composition in the transgenics are still ~40% protein/ 18% oil as in wildtype but the proteins making up the proteome have been altered.  We have also engineered soybean seeds via RNAi to suppress only the beta-conglycicin storage protein (RNAiBC), and like the RNAiSP seeds they also contain wildtype levels of oil and protein and their seed protein content composition also has changed to now contain increasing levels of alternate compensating proteins.  Interestingly, although the RNAiSP plants have no visible phenotypes, the RNAiBC plants display a number of altered phenotypes compared to wildtype plants, namely dark hilium, white-to-purple flower color, change in leaf morphology and dwarf stature.  These plant phenotypes displayed in RNAiBC, but not RNAiSP, plants can most readily be explained by epigenetic events.  Methylation analysis of the RNAiBC and RNAiSP genomes compared to wildtype revealed a marked, 3-fold, increase in global methylation.  The comparison of the maps of methylation in the genomes of RNAiBC and RNAiSP compared to wildtype will give insights to the mechanism of protein compensation in the seeds and to the RNAiBC plant phenotypes that cannot be explained by the introduced transgene.