Nodulation and Nodulin Gene Expression in an Interspecific Hybrid Between Glycine max and Glycine tomentella

Abstract

When the genome of a wild species, Glycine tomentella, is combined with that of the cultivated soybean, Glycine max in a hybrid, nodulation specificity is altered. Two strains of Rhizobium fredii that nodulate the G. rnax parent fail to nodulate the hybrid, indicating the presence of a restriction gene, while three Bradyrhizobium japonicum strains that nodulate G. max are highly effective on the hybrid. Some strains of (Brady)rhizobium, originally isolated from wild Australian Glycine species, nodulate only one of the two parental species. One strain ineffective on G. max is effective on the hybrid. Two other strains, while effective on one parent, appear more effective on the hybrid. In three fully examined cases in which effective nodules are produced on the hybrid, the late nodulins leg-hemoglobin, glutamine synthetase, and xanthine dehydrogenase are expressed from both genomes. Thus, although a rhizobial strain may nodulate only one or the other of the parental types, if it successfully nodulates the hybrid, the nodulation process provides signals or internal conditions that lead to expression of late nodulins from both genomes.