Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/2/2012
Publication Date: 12/1/2012
Citation: Radwan, O., Wu, X., Govindarajulu, M., Libault, M., Neece, D.J., Berg, H.R., Stacey, G., Taylor, C.G., Huber, S.C., Clough, S.J. 2012. 14-3-3 Proteins SGF14c and SGF14l play critical roles during soybean nodulation. Plant Physiology. 160:2125-2136. Interpretive Summary: Legume plants utilize a symbiotic relationship with bacteria to convert inactive atmospheric nitrogen gas into utilizable ammonia within plant outgrowths on the roots called nodules. Because of this sybiotic nitrogen fixation, legume plants can grow well in nitrogen-poor soils. Understanding how nodulation works is enhanced by understanding the genes that are required to make the proteins that are critical to make a functional nodule. In this work, we identified one such gene, a gene that encodes for a protein called a '14-3-3 protein' that is involved in activating or inactivating other proteins. Without the expression of this gene, we found that nodules do not fully develop, and therefore, this is another gene critical to nodulation. This work will be of interest to plant pathologists, microbiologists, and molecular plant biologists.
Technical Abstract: The soybean (Glycine max L. Merr.) genome contains 18 members of the 14-3-3 protein family, but little is known about their association with specific phenotypes. Here, we report that the Glyma0529080 (SGF14c) gene, encoding a 14-3-3 protein, appears to play an essential role in soybean nodulation. QRT-PCR and western immunoblot analyses showed that SGF14c mRNA and protein levels were specifically increased in abundance in nodulated soybean roots 16, 24 and 32 days after inoculation with Bradyrhizobium japonicum. To investigate the role of SGF14c during soybean nodulation, RNA interference (RNAi) was employed to silence SGF14c expression in soybean roots using Agrobacterium rhizogenes-mediated root transformation. Due to the palaeopolyploidy nature of soybean, designing a specific RNAi sequence that exclusively targeted SGF14c was not possible. Therefore, two highly similar paralogs (SGF14c and SGF14l), that have been shown to function as dimers, were silenced. Transcriptomic and proteomic analyses showed that mRNA and protein levels were significantly reduced in the SGF14c/SGF14l silenced roots and these roots exhibited reduced numbers of mature nodules. In addition, SGF14c/SGF14l silenced roots contained large numbers of arrested nodule primordia following B. japonicum inoculation. Transmission electron microscopy further revealed that the host cytoplasm was severely degraded in the failed nodules, and that all membranes, except the symbiosome membrane, were missing within the arrested nodules.