Nodulation genes

A. Nodulation genes—production of nod factors Flavonoids Rhizobium spp. 90,91.92... 

A. J. Dharmatilake and W. D. Baker, Cheinotaxis of Rhizohium meliloti towards nodulation gene inducing compounds from alfalfa roots. Applied and Environmental Microbiology 5S 1153 (1992). 

B. G. Rolfe, Flavones induce expression of nodulation genes in Rhizobium, Nature 323 632 (1986). 

Table 2 Biochemical Function of Nodulation Gene Products Involved in Nod Fiictor Synthesis and Transport...

N. R. Peters and S. R. Long, Alfalfa root exudates and compounds which promote or inhibit induction of Rhizohium nteliloti nodulation genes. Plant Phy.siol 88 296 (1988). 

Z. Banfalvi and A. Kondorosi, Production of root hair deformation factors by Rhizohium meliloti nodulation genes in Escherichia coli H.mD (NocM) is involved in the plant host-specific modification of the NodABS-factor. Plant Mol. Biol. 13 1 (1989). 

A. Economou, W. D. O. Hamilton, A. W. B. Johnston, and J. A. Downie, The Rhizohium nodulation gene nodO encodes a Ca -binding protein that is exported without N-terminal cleavage and is homologous to haemolysin and related proteins. EMBO J. 9 ,349 (1990). 

J. A. Downie, A. Economou, A. K. Scheu, A. W. B. John.son, J. L. Firmin, K. E. Wilson, M. T. Cubo, A. Mavridou, C. Marie, A. Davies and B. P. Surin, The Rhizohium legumino.sarum bv. viciae NodO protein compensates for the exported signal made by the host-specific nodulation genes. Nitrogen Fixation Achievements and... 

Nevertheless, cereal plants can interact with endosymbionts, capable of nitrogen fixation in other species, and be stimulated in their productivity. The odds of soil life are balanced for some bacteria by their interactivity at rhizosphere level, and a realm of exchanged signals dictates entry into hormonally reprogrammed root sites. Specificity for partner plant species is part of a fine speciation process that actively involves the bacterial nodulation genes, and continues to drive their variation dynamics. 

G. Gaetano-Anolles, D. K. Christ-E.stes, and W. D. Bauer, Chemotaxis of Rhizobiiim meliloti to the plant flavone luleolin requires functional nodulation genes. J. Bacte-riol. 170 3164-3169 (1988). 

B. D. H. Jarvis, L. J. H. Ward, and E. A. Slade, Expression by soil bacteria of nodulation genes from Rhizobium leguminosarum biovar trifolii. Appl. Environ. Microbiol. 55 1426-1434 (1989). 

Recently, a new polyketide biosynthetic pathway in bacteria that parallels the well studied plant PKSs has been discovered that can assemble small aromatic metabolites.8,9 These type III PKSs10 are members of the chalcone synthase (CHS) and stilbene synthase (STS) family of PKSs previously thought to be restricted to plants.11 The best studied type III PKS is CHS. Physiologically, CHS catalyzes the biosynthesis of 4,2, 4, 6 -tetrahydroxychalcone (chalcone). Moreover, in some organisms CHS works in concert with chalcone reductase (CHR) to produce 4,2 ,4 -trihydroxychalcone (deoxychalcone) (Fig. 12.1). Both natural products constitute plant secondary metabolites that are used as precursors for the biosynthesis of anthocyanin pigments, anti-microbial phytoalexins, and chemical inducers of Rhizobium nodulation genes.12... 

Maxwell, C.A. et al., Molecular characterization and expression of isoliquiritigenin 2 -0-methyltransferase, an enzyme specifically involved in the biosynthesis of an inducer of Rhizobium meliloti nodulation genes. Plant J., 4, 971, 1993. 

Peters, N.K., Frost, J.W., and Long, S.R., A plant flavone, luteolin, induces expression of Rhizobium meliloti nodulation genes, Science, 233, 917, 1986. 

Spaink, H.P. et al., Rhizobium nodulation gene nodD as a determinant of host specificity, Nature, 328, 337, 1987. 

Firmin, J.L. et al., Flavonoid activation of nodulation genes in Rhizobium reversed by other compounds present in plants. Nature, 324, 90, 1986. 

Caetano-Anolles, G., Christ-Estes, D.K., and Bauer, W.D., Chemotaxis of Rhizobium meliloti to the plant flavone luteolin requires functional nodulation genes, J. Bacteriol, 170, 3164, 1988. 

Horvath B., Bachem, C.W.B., Schell, J. Kondorosi, A. (1987). Host-specific regulation of nodulation genes in Rhizobium is mediated by a plant-signal interacting with the nodD gene product. The EM BO Journal 6, 841-8. 

Kondorosi, A. (1991). Regulation of nodulation genes in Rhizobium. In Molecular Signals in Plant-Microbe Communication, ed. D.P.S. Verma pp. 325-40. Boca Raton, FL CRC Press. 

Apigenin (70b), luteolin (70c) and related polyhydroxyflavones can activate the nodulation genes of the nitrogen-fixation bacteria (genus Rhizobium) in the leguminous plants such as peas. This is the first time that simple flavonoids have been shown to be involved in gene regulation [367-369]. 

Legumes also secrete antagonists that inhibit the flavonoid-mediated activation of nodulation genes (Table 2).63 64 Some act as inducers in another symbiotic system. Antagonists generally have structures similar to those of inducers and inhibition can be overcome by increasing the concentration of inducers, hence they are considered as competitive inhibitors.63... 

Table 1 Nodulation gene inducers secreted by leguminous plants61...

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