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First published online December 23, 2005; 10.1104/pp.105.070326 Plant Physiology 140:221-234 (2006) © 2006 American Society of Plant Biologists
Transcript Analysis of Early Nodulation Events in Medicago truncatula1,2,[W]Department of Plant Biology (D.P.L., N.S., K.A.T.S., K.A.V.), Department of Plant Pathology (S.P., D.S.), and Microbial and Plant Genomics Institute (D.S., K.A.V.), University of Minnesota, Saint Paul, Minnesota 55108; Biological Research Center of the Hungarian Academy of Sciences, Institute of Genetics, H–6726 Szeged, Hungary (G.E.); United States Department of Agriculture, Agricultural Research Service, Plant Science Research Unit, Saint Paul, Minnesota 55108 (D.S.); and The Institute for Genomic Research, Rockville, Maryland 20850 (C.T.)
Within the first 72 h of the interaction between rhizobia and their host plants, nodule primordium induction and infection occur. We predicted that transcription profiling of early stages of the symbiosis between Medicago truncatula roots and Sinorhizobium meliloti would identify regulated plant genes that likely condition key events in nodule initiation. Therefore, using a microarray with about 6,000 cDNAs, we compared transcripts from inoculated and uninoculated roots corresponding to defined stages between 1 and 72 h post inoculation (hpi). Hundreds of genes of both known and unknown function were significantly regulated at these time points. Four stages of the interaction were recognized based on gene expression profiles, and potential marker genes for these stages were identified. Some genes that were regulated differentially during stages I (1 hpi) and II (6–12 hpi) of the interaction belong to families encoding proteins involved in calcium transport and binding, reactive oxygen metabolism, and cytoskeleton and cell wall functions. Genes involved in cell proliferation were found to be up-regulated during stages III (24–48 hpi) and IV (72 hpi). Many genes that are homologs of defense response genes were up-regulated during stage I but down-regulated later, likely facilitating infection thread progression into the root cortex. Additionally, genes putatively involved in signal transduction and transcriptional regulation were found to be differentially regulated in the inoculated roots at each time point. The findings shed light on the complexity of coordinated gene regulation and will be useful for continued dissection of the early steps in symbiosis.
1 This work was supported by the National Science Foundation Plant Genome Project (award no. 0110206) and by the University of Minnesota. 2 Mention of trade names or commercial products in the article is solely for the purpose of providing specific information and does not imply recommendations or endorsement by the U.S. Department of Agriculture. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Kathryn A. VandenBosch (vande102{at}umn.edu). [W] The online version of this article contains Web-only data. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.070326. * Corresponding author; e-mail vande102{at}umn.edu; fax 612–625–1738. Received August 24, 2005; returned for revision November 3, 2005; accepted November 9, 2005. This article has been cited by other articles:
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