|Lee, Mei Phing|
Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2008
Publication Date: 6/1/2008
Citation: Brechenmacher, L., Moon-Young, K., Zou, J., Benitez, M., Li, M., Joshi, T., Calla, B., Lee, M., Philip, R., Libault, M., Vodkin, L.O., Xu, D., Lee, S., Clough, S.J., Stacey, G. 2008. Transcription profiling of soybean nodulation by Bradyrhizobium japonicum. Molecular Plant-Microbe Interactions. 21(5):631-645.
Interpretive Summary: Legumes interact with nodulating bacteria to convert atmospheric nitrogen into ammonia for plant use. This nitrogen fixation takes place within root nodules that form after infection of root hairs by compatible rhizobium. Although nodule development and nitrogen fixation are important biological processes, little is know as to what genes play an important role in these processes. This paper screened about 40,000 genes for their expression levels during early interactions between the nodulating bacterium Bradyrhizobium japonicum and soybean. Our analyses identified that the over 6,500 genes changed expression patterns in a soybean root during the first 72 hours of inoculation with B. japonicum. In addition to identifying many genes related to general metabolism and cellular biology, we also identified many genes related to pathogen defense. This finding shows that symbiotic bacteria do induce some defenses but that many defense-related genes are shut down allowing the symbiosis to succeed.
Technical Abstract: Legumes interact with nodulating bacteria to convert atmospheric nitrogen into ammonia for plant use. This nitrogen fixation takes place within root nodules that form after infection of root hairs by compatible rhizobium. Using cDNA microarrays, we monitored gene expression in soybean (Glycine max) inoculated with the nodulating bacterium Bradyrhizobium japonicum during the early stages (0 to 72 hours post inoculation (hpi) and late stages (4 to 16 days) after inoculation (dai) of the nitrogen-fixing symbiosis. Twenty five genes were found to be significantly regulated during the early stages of nodulation. This low number is likely the result of the tightly localized inoculation response and the tissue dilution that occurred when the soybean roots were processed. Therefore, our second experiment focused on later time points that coincided with nodule development and onset of nitrogen fixation. This experiment identified several thousand genes that were differentially expressed in response to B. japonicum inoculation. One general finding from the microarray data was that B. japonicum reduced plant defense reactions during nodule development. In addition, the data revealed a high level of regulatory complexity that is likely essential for development of the symbiosis and adjustment to an altered nutritional status.