Date of Award
Master of Science
Nodulation is an important process in legume-rhizobium symbiotic nitrogen fixation. This thesis demonstrates our investigation of genes involved in soybean nodulation.
In the first project, we studied the molecular mechanisms contributing to an abnormal-nodulation phenotype of a soybean T-DNA insertion mutant, 454-4. Genetic analysis showed that T-DNAs are integrated into two loci of 454-4 genome, nodulation signaling pathway 2 (GmNSP2a), and GmEREACTA. Since GmNSP2a is orthologous to NSP2 proteins from Medicago truncatula and Lotus japonicus that are essential for nodulation, we speculated that the abnormal nodulation phenotype of 454-4 is due to the T-DNA insertions at GmNSP2a. To test it, overexpression and RNA interference (RNAi) constructs of GmNSP2a were respectively introduced into wild-type soybean, while neither construct altered the number of nodules in these transgenic plants. From F2 population of 454-4, we isolated two mutants, tNSP2 and tEREACTA, carrying T-DNAs at either GmNSP2a or GmEREACTA. Neither tNSP2 nor tEREACTA exhibited abnormal nodulation. Moreover, some F2 plants of the cross between tNSP2 and tEREACTA exhibited abnormal nodulation. Based on these results, we proposed that the abnormal nodulation of 454-4 is due to the combinational effects of T-DNA insertions at GmNSP2a and GmEREACTA. In addition, we established the protocol of Agrobacterium rhizogenes-mediated soybean transformation in our lab to prepare for the complementation of 454-4.
In the second project, we investigated whether phytohormone brassinosteroids (BRs) regulate soybean nodulation. Brassinolide (a type of BRs) and brassinazole (a biosynthesis inhibitor of BRs) were applied to wild-type soybean plants respectively, and neither treatment significantly altered the number of nodules in these plants. Soybean BR genes were predicted by Basic Local Alignment Search Tool (BLAST) searches. The expression profiles of these putative genes were obtained. To investigate whether BR genes have function in soybean nodulation, overexpression and RNAi constructs of some putative soybean BR genes were introduced into soybean respectively and the transgenic plants were successfully generated. The next step is to examine their phenotypes including nodulation.
Yang, Chichun, "Investigation of genes involved in the formation of nitrogen-fixing nodules in soybean" (2013). Graduate Theses and Dissertations. 13254.