Functional Genomics of Root Hair Infection project publications (MU)

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https://hdl.handle.net/10355/53194

This NSF-funded project uses functional genomics to investigate the process of legume root hair infection by nitrogen-fixing rhizobia. This infection initiates the symbiosis between this bacterium and its host that will result in the de novo formation of a novel organ, the nodule. It is within the nodule that the bacterium fixes nitrogen providing its host plant an advantage in environments where this element is limiting. The establishment of the symbiosis involves a complex interplay between host and symbiont, which is orchestrated by the exchange of diffusible signal molecules.

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Distinct, crucial roles of flavonoids during legume nodulation
(Elsevier, 2007-06) Subramanian, Senthil; Stacey, Gary, 1951-; Yu, Oliver
RNA interference-mediated silencing of the key flavonoid and isoflavone biosynthesis enzyme, respectively, by two different research groups has provided direct genetic evidence for the essential roles that these compounds play in nodulation. Anton Wasson et al. have shown that flavonoids are essential for localized auxin transport inhibition during nodulation in the indeterminate legume Medicago truncatula. By contrast, Senthil Subramanian et al. have shown that isoflavones are essential for endogenous nod gene induction in the determinate legume soybean.
Genetics and functional genomics of legume nodulation
(Elsevier, 2006-02) Stacey, Gary, 1951-; Libault, Marc; Brechenmacher, Laurent; Wan, Jinrong; May, Gregory D.
Gram-negative soil bacteria (rhizobia) within the Rhizobiaceae phylogenetic family (a-proteobacteria) have the unique ability to infect and establish a nitrogen-fixing symbiosis on the roots of leguminous plants. This symbiosis is of agronomic importance, reducing the need for nitrogen fertilizer for agriculturally important plants (e.g. soybean and alfalfa). The establishment of the symbiosis involves a complex interplay between host and symbiont, resulting in the formation of a novel organ, the nodule, which the bacteria colonize as intracellular symbionts. This review focuses on the most recent discoveries relating to how this symbiosis is established. Two general developments have contributed to the recent explosion of research progress in this area: first, the adoption of two genetic model legumes, Medicago truncatula and Lotus japonicus, and second, the application of modern methods in functional genomics (e.g. transcriptomic, proteomic and metabolomic analyses).
Proteomic Analysis of Soybean Root Hairs After Infection by Bradyrhizobium japonicum
(APS Press, 2005-01) Wan, Jinrong; Torres, Michael; Ganapathy, Ashwin; Thelen, Jay J.; DaGue, Beverly B.; Mooney, Brian P.; Xu, Dong, 1965-; Stacey, Gary, 1951-
Infection of soybean root hairs by Bradyrhizobium japonicum is the first of several complex events leading to nodulation. In the current proteomic study, soybean root hairs after inoculation with B. japonicum were separated from roots. Total proteins were analyzed by two-dimensional (2-D) polyacrylamide gel electrophoresis. In one experiment, 96 protein spots were analyzed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) to compare protein profiles between uninoculated roots and root hairs. Another 37 spots, derived from inoculated root hairs over different timepoints, were also analyzed by tandem MS (MS/MS). As expected, some proteins were differentially expressed in root hairs compared with roots (e.g., a chitinase and phosphoenolpyruvate carboxylase). Out of 37 spots analyzed by MS/MS, 27 candidate proteins were identified by database comparisons. These included several proteins known to respond to rhizobial inoculation (e.g., peroxidase and phenylalanine-ammonia lyase). However, novel proteins were also identified (e.g., phospholipase D and phosphoglucomutase). This research establishes an excellent system for the study of root-hair infection by rhizobia and, in a more general sense, the functional genomics of a single, plant cell type. The results obtained also indicate that proteomic studies with soybean, lacking a complete genome sequence, are practical.

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