Transcriptional Activation in Nuclei from Uninfected Soybean of a Set of Genes Involved in Symbiosis with Rhizobium. Vincent P. Mauro. Centre for Plant Molecular Biology, Department of Biology, McGill University, Montreal, Quebec H3A 1B1 Canada. Desh Pal S. Verma. Centre for Plant Molecular Biology, Department of Biology, McGill University, Montreal, Quebec H3A 1B1 Canada.. MPMI 1:46-51. Accpted 19 October 1987. Copyright 1987 The American Phytopathological Society.

Several plant genes coding for nodule-specific proteins, nodulins, are expressed in legume root nodules during symbiotic nitrogen fixation. We have found that three coordinately regulated nodulin genes of soybean are transcriptionally activated following incubation of nuclei from an uninfected tissue with nodule extract. Transcription in isolated nuclei was monitored following addition of Escherichia coli RNA polymerase, which appears to transcribe active regions of chromatin. The kinetics of induction were similar for nodulin-23, nodulin-24, and leghemoglobin c3 genes but different from nodulin-35, a gene induced in the uninfected cells later in nodule development. Detailed analysis of the transcripts from one of the nodulin genes showed that preferential transcription occurred in the 5’ region, suggesting that a factor present in nodule extract is able to alter chromatin structural domains encoding nodulin genes that allow transcription from this region of the genome. In vitro activation of these nodulin genes is specific to nodule extract; free living Rhizobium and any other plant extracts or incubation conditions do not have any effect. These data indicate that a transactivating factor of bacterial or plant origin is produced following infection by Rhizobium and is involved in the induction of nodulin genes.