Date: February 3, 2012
Time: 1:30 PM
Location: Bioinformatics 105
Title: Good Use of Genomic Resources and Biotechnologies to Investigate Soybean Biology
Marc Libault, Ph.D.
Assistant Professor of Botany
Department of Botany & Microbiology
University of Oklahoma
Abstract: A milestone in soybean research was the sequencing of its genome. The sequence predicts 69,145 putative soybean genes. In order to examine their expression, we utilized the Illumina Solexa platform to sequence cDNA derived from 14 conditions. The result is a searchable soybean gene expression atlas accessible through a browser (http://digbio.missouri.edu/soybean_atlas/). The analysis of this atlas reveals strong differences in gene expression patterns between different tissues as well as in root hair cells in response to infection by Bradyrhizobium japonicum, the compatible symbiotic bacterium.
These transcriptome data were used as the basis to identify genes potentially important soybean development including the nodulation process. The function of these nodulation genes was examined by RNAi-based gene silencing using Agrobacterium rhizogenes hairy root transformation. The nodulation genes identified using this approach include GmFWL1 (FW2.2-like 1), a soybean homolog of the tomato FW2.2 gene which controls 30% of the variance in fruit weight, as well as GmNMNa (Nucleolar/Mitochondrial protein involved in Nodulation a) encoding a protein of unknown function.
Using qRT-PCR and transcriptional fusions between the GmFWL1 and GmNMNa promoters and the reporter genes GFP and GUS, we demonstrated both genes were expressed only in a small number of root hair cells in response to B. japonicum inoculation and specifically in nodules. Consistent with their induction during nodulation, the silencing of the expression of these genes resulted in a significant reduction in nodule formation. In addition, the silencing of GmFWL1 expression led to a decrease in nuclear size and modifications of chromatin structure, while the knockdown of GmNMNa expression resulted in the decrease of bacteroid numbers and the level of poly-beta-hydroxybutyrate (PHB) granules in each bacteroid compared to the control. These data indicate that both GmFWL1 and GmNMNa genes are critical for soybean nodulation.
Libault M, Govindarajulu M, Berg H, Ong YT, Puricelli K, Taylor CG, Xu D and Stacey G. (2011) A dual-targeted soybean protein is essential for Bradyrhizobium japonicum infection of soybean root hair and cortical cells. Mol Plant-Microbe Interact. 24(9):1051-60.
Libault M, Zhang XC, Govindarajulu M, Ong YT, Brechenmacher L, Berg H, Hurley-Sommer A, Qiu J, Taylor CG and Stacey G. (2010) A member of the highly conserved FWL (tomato FW2.2-like) gene family is essential for soybean nodule organogenesis. The Plant Journal. 62(5):852-64.
Libault M, Farmer A, Joshi T, Takahashi K, Langley RJ, Levi FD, He J, Xu D, May GD and Stacey G. (2010) An integrated transcriptome atlas of the crop model Glycine max and its use in comparative analyses in plants. The Plant Journal. 63(1):86-99.
Libault M, Farmer A, Brechenmacher L, Drnevich J, Langley RJ, Bilgin DD, Radman O, Neece DJ, Clough SJ, May GD and Stacey G. (2010) Complete transcriptome of soybean root hair cell, a single cell model, and its alteration in response to Bradyrhizobium japonicum infection. Plant Physiol. 152(2):541-52. Plant Systems Biology Special Issue 2010.