Three regulatory nodD alleles of diverged flavonoid-specificity are involved in host-dependent nodulation by Rhizobium meliloti

Györgypál, Zoltán; Iyer, Narayan V.; Kondorosi, Ádám

doi:10.1007/bf00322448

Cited by 106 publications

(68 citation statements)

References 46 publications

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“…Effective rhizobial cells present in that soil region, or those attracted to it by their chemotactic movement toward luteolin (2), will be exposed to a combination of these two strong nod gene inducers, and a synergistic transcription of nod genes similar to that shown in Figure 4 may occur. Although the molecular basis of such interactions is unknown, some published results suggest that various functional copies of nodD in R. meliloti (9) interact with different unknown factors (7). Thus, luteolin and 4,4'-dihydroxy-2'-methoxychalcone may influence rhizobial cells through different nodD alleles.…”

Section: Flavonoid Nod Gene Inducersmentioning

confidence: 99%

Interactions among Flavonoid nod Gene Inducers Released from Alfalfa Seeds and Roots

Hartwig

Maxwell²,

Joseph³

et al. 1989

Plant Physiol.

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Alfalfa (Medicago sativa L.) seeds and roots can create complex rhizosphere effects by releasing flavonoids that induce nodulation (nod) genes in Rhizobium meIiIoti. Previous reports identified luteolin and 4,4'-dihydroxy-2'-methoxychalcone as strong inducers that are released from seeds and roots, respectively, and 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone as weaker inducers which are exuded by roots. As a first step toward identifying flavonoid interactions that may occur in the rhizosphere, combinations of these molecules were tested for transcriptional effects on a nodABC-lacZ fusion in R. meliloti. At low concentrations (e.g. 8.4 nanomolar), interactions of the three nod gene inducers from root exudate were additive. When the strong inducers 4,4'-dihydroxy-2'-methoxychalcone and luteolin were present separately at higher concentrations (e.g. 21 nanomolar), their effect could be decreased significantly by the weaker inducers 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone. In contrast, when low concentrations of luteolin from seed rinses and 4,4'-dihydroxy-2'-methoxychalcone from root exudate were present together, they produced synergistic increases in nod gene transcription. Tests with mixtures of the three nod gene inducers from root exudate indicated that alfalfa seedlings might easily decrease the strong inductive effect of the chalcone by releasing modest amounts of the weaker inducers. In addition, mixtures of luteolin and the nod gene inducers in root exudate suggested that interactions between nod gene inducers from seeds and roots may create a zone highly favorable to root nodule formation near the top of the primary root.

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Section: Flavonoid Nod Gene Inducersmentioning

confidence: 99%

Interactions among Flavonoid nod Gene Inducers Released from Alfalfa Seeds and Roots

Hartwig

Maxwell²,

Joseph³

et al. 1989

Plant Physiol.

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“…They indicate that not all nod gene inducers from alfalfa show similar patterns of nodABC-lacZ induction with additional copies of nodDI or nodD2 genes (Tables 1 and 2). Recent work with alfalfa seed rinses indicated that an unknown factor(s) induced transcription through nodDI and nodD2 (5). All of the natural nod gene inducers from alfalfa discussed in this report were identified by their capacity to activate NodDl protein (7,18), but only one of those compounds, the methoxychalcone, also produced high levels of nod gene induction in the presence of extra NodD2 protein (Table 2).…”

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confidence: 67%

“…One well-described transcriptional unit, the nodABC genes, initiates cortical cell division (2, 26), root hair deformation (15), and production of a receptorlike protein (12,13). The nodABC genes in R. meliloti are expressed primarily in the presence of particular flavonoids exuded by alfalfa seeds or roots (7, 18, 21,23).Precisely how plant flavonoids induce transcription of nod genes in R. meliloti is not known, but a family of regulatory genes including nodDI, nodD2, and nodD3 is involved (4,5,9,22,25). Studies of the nodDi gene product (NodDl), nod gene-inducing flavonoids, and the promoter region of nod-ABC suggest that NodDl is a DNA-binding protein (3,8,16).…”

mentioning

confidence: 99%

“…Precisely how plant flavonoids induce transcription of nod genes in R. meliloti is not known, but a family of regulatory genes including nodDI, nodD2, and nodD3 is involved (4,5,9,22,25). Studies of the nodDi gene product (NodDl), nod gene-inducing flavonoids, and the promoter region of nod-ABC suggest that NodDl is a DNA-binding protein (3,8,16).…”

mentioning

confidence: 99%

“…Studies of the nodDi gene product (NodDl), nod gene-inducing flavonoids, and the promoter region of nod-ABC suggest that NodDl is a DNA-binding protein (3,8,16). Tests with crude seed exudates from different plant species nodulated by R. meliloti indicate that species-specific factors interact with different NodD proteins (5). In those tests, alfalfa seed exudate produced high levels of nod gene induction in the presence of nodDi, nodD2, and nodD3, but it could not be determined whether the same or separate (presumably flavonoid) factors functioned through different nodD genes.…”

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confidence: 99%

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Effects of alfalfa nod gene-inducing flavonoids on nodABC transcription in Rhizobium meliloti strains containing different nodD genes

et al. 1990

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Transcription of the nodulation genes nodABC in Rhizobium meliloti requires a plant flavonoid signal and nodD, a family of bacterial regulatory genes (nodDl, nodD2, and nodD3). Results from this study show that all previously identified nod gene inducers released by alfalfa seeds and roots induced nodABC-IacZ transcription in R. meliloti containing extra copies of nodDI, but only 4,4'-dihydroxy-2'-methoxychalcone gave high levels of induction with extra copies of nodD2. While mixtures of the methoxychalcone and luteolin showed a positive synergism with extra NodDl protein, they apparently competed for binding to the NodD2 protein.Rhizobium meliloti infect alfalfa (Medicago sativa L.) plants and induce the formation of root nodules that reduce N2 to ammonia. Several sets of bacterial genes are involved in the early stages of nodule formation. One well-described transcriptional unit, the nodABC genes, initiates cortical cell division (2, 26), root hair deformation (15), and production of a receptorlike protein (12,13). The nodABC genes in R. meliloti are expressed primarily in the presence of particular flavonoids exuded by alfalfa seeds or roots (7, 18, 21,23).Precisely how plant flavonoids induce transcription of nod genes in R. meliloti is not known, but a family of regulatory genes including nodDI, nodD2, and nodD3 is involved (4,5,9,22,25). Studies of the nodDi gene product (NodDl), nod gene-inducing flavonoids, and the promoter region of nod-ABC suggest that NodDl is a DNA-binding protein (3,8,16). Tests with crude seed exudates from different plant species nodulated by R. meliloti indicate that species-specific factors interact with different NodD proteins (5). In those tests, alfalfa seed exudate produced high levels of nod gene induction in the presence of nodDi, nodD2, and nodD3, but it could not be determined whether the same or separate (presumably flavonoid) factors functioned through different nodD genes.A series of flavonoids has now been identified as natural alfalfa nod gene inducers in R. meliloti 1021(pRmM57), which contains a cloned fragment with a nodDIABC-lacZ fusion (21). Luteolin (3',4',5,7-tetrahydroxyflavone; Fig. 1), which was first isolated from alfalfa seeds (23), was not found in root exudates of Moapa 69 alfalfa seedlings (18). However, the root exudates did contain three other nod gene inducers: 4,4'-dihydroxy-2'-methoxychalcone, 4',7-dihydroxyflavone, and 4',7-dihydroxyflavanone ( Fig. 1) (18). Seed rinses from the same alfalfa cultivar contained luteolin and chrysoeriol (3'-methoxyluteolin; Fig. 1) (7). The biological significance of this diversity of nod gene inducers is not clear, but at least three points are noteworthy. First, although luteolin probably is the most prevalent nod gene inducer in the soil around a germinating alfalfa seed (7), the methoxychalcone and chrysoeriol induce half-maximum transcriptional rates of nodABC-lacZ fusion at 10 and 25%, respectively, of the concentration required for luteolin (7, 18). Second, the 4',7 substitution pattern (flavone numberin...

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Transduction of plant signal molecules by the Rhizobium NodD proteins

1991

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Three regulatory nodD alleles of diverged flavonoid-specificity are involved in host-dependent nodulation by Rhizobium meliloti

Cited by 106 publications

References 46 publications

Interactions among Flavonoid nod Gene Inducers Released from Alfalfa Seeds and Roots

Interactions among Flavonoid nod Gene Inducers Released from Alfalfa Seeds and Roots

Effects of alfalfa nod gene-inducing flavonoids on nodABC transcription in Rhizobium meliloti strains containing different nodD genes

Transduction of plant signal molecules by the Rhizobium NodD proteins

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