IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Monday 28 November 2011
Concurrent Session 2 – Function & Control of Nitrogenase
1530 - 1650
Authors: Svetlana N. Yurgel 1 , Jennifer Rice 1 , and Michael L. Kahn 1,2
1 Institute of Biological Chemistry,Washington State University, Pullman, WA. 99164.
2 School of Molecular Biosciences,Washington State University, Pullman, WA. 99164.
Presentation Title: GlnD and symbiosis: Control beyond the nitrogen stress response?
Presentation Time: 1610 - 1630
To establish an effective symbiosis with alfalfa, S. meliloti Rm1021 needs normal operation of the GlnD protein, a
bifunctional uridylyltransferase/uridylyl-cleavage enzyme that measures cellular nitrogen status and initiates a
nitrogen stress response (NSR) (Yurgel & Kahn 2008). Both of the two known targets of GlnD modification, the
PII proteins GlnB and GlnK, are not needed for effectiveness (Yurgel et al., 2010). However, the glnD-sm2
mutation that leads to a Fix+Eff¯ phenotype is defective in uridylylation and cells are thought to only have
unmodified PII proteins. To generate GlnB in the state expected in a glnD-sm2 mutant, we introduced a
Tyr�Phe variant of GlnB that cannot be uridylylated into a glnBglnK background and found that this strain was
Fix+Eff+. We also generated a glnBglnKglnD triple mutant and used this and other mutants to dissect the role of
these proteins in regulating the free-living NSR and nitrogen metabolism in symbiosis. The glnD-sm2 mutation
was dominant to the glnBglnK mutations in symbiosis but recessive in some free-living phenotypes. The data
show that the GlnD protein has a role in free-living growth and in symbiotic nitrogen exchange that does not
depend on the PII proteins, suggesting that S. meliloti GlnD can communicate information to the cell by alternate
mechanisms.
Yurgel SN & Kahn ML (2008). A mutant GlnD nitrogen sensor protein leads to a nitrogen-fixing but ineffective
Sinorhizobium meliloti symbiosis with alfalfa. Proc Natl Acad Sci U S A 105(48):18958-18963.
Yurgel SN, Rice J, Mulder M & Kahn ML (2010). GlnB/GlnK PII proteins and regulation of the Sinorhizobium
meliloti Rm1021 nitrogen stress response and symbiotic function. J Bacteriol 192:2473-2481.
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2011