Flavones induce expression of nodulation genes in Rhizobium

Redmond, John W.; Batley, Michael; Djordjevic, Michael A.; Innes, Roger W.; Kuempel, Peter L.; Rolfe, Barry G.

doi:10.1038/323632a0

Cited by 474 publications

(221 citation statements)

References 18 publications

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“…Those compounds are not found in alfalfa root exudates, but other flavonoid nod-gene inducers, 4,4'-dihydroxy-2'-methoxychalcone, 4',7-dihydroxyflavone, and 4',7-dihydroxyflavanone, are present (20). Related flavonoids can induce nodgene transcription in other Rhizobium and Bradyrhizobium species (2,7,16,25,26,30).…”

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confidence: 99%

Concurrent Synthesis and Release of nod-Gene-Inducing Flavonoids from Alfalfa Roots

Maxwell

Phillips

1990

Plant Physiol.

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Flavonoid signals from alfalfa (Medicago sativa L.) induce transcription of nodulation (nod) genes in Rhizobium meliloti. Alfalfa roots release three major nod-gene inducers: 4',7-dihydroxyflavanone, 4',7-dihydroxyflavone, and 4,4'-dihydroxy-2'-methoxychalcone. The objective of the present study was to define temporal relationships between synthesis and exudation for those flavonoids. Requirements for concurrent flavonoid biosynthesis were assessed by treating roots of intact alfalfa seedlings with [U-14C]-L-phenylalanine in the presence or absence of the phenylalanine ammonia-lyase inhibitor L-2-aminoxy-3-phenylpropionic acid (AOPP). In the absence of AOPP, each of the three flavonoids in exudates contained 14C. In the presence of AOPP, 14C labeling and release of all the exuded nod-gene inducers were reduced significantly. AOPP inhibited labeling and release of the strongest nod-gene inducer, methoxychalcone, by more than 90%. Experiments with excised cotyledons, hypocotyls, and roots incubated in solution showed that the flavonoids could be synthesized in and released from each organ. However, the ratio of the three flavonoids in exudates from intact plants was most similar to the ratio recently synthesized and released from excised roots. A portion of recentiy synthesized flavonoid aglycones was found conjugated, presumably as glycosides, in root extracts and may have been involved in the release process. Data from root extracts showed that formononetin, an isoflavonoid which does not induce nod genes, was present in conjugated and aglycone forms but was not released by normal intact roots. In contrast, roots stressed with CuCI2 did release the aglycone formononetin. Thus, the release process responsible for exudation of nod-gene inducers appears to be specific rather than a general phenomenon such as a sloughing off of cells during root growth. The synthesis and specific concurrent release of flavonoid nod-gene inducers in this study is consistent with the physiological requirement for nodule formation of the 3-day-old seedlings used.Alfalfa (Medicago sativa L.), an important leguminous forage crop, forms N2-fixing root nodules in association with the soil bacterium Rhizobium meliloti. Early events of alfalfa nodule formation require expression of nodulation genes including nodDABC on the megaplasmid of R. meliloti (6,15). Transcription of nodABC is induced through the cooperative action of the protein product of the nodD gene and components of root and seed exudates (21). Luteolin, '

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confidence: 99%

Concurrent Synthesis and Release of nod-Gene-Inducing Flavonoids from Alfalfa Roots

Maxwell

Phillips

1990

Plant Physiol.

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“…One observation that has been consistent among independent laboratories is that the root tip is rich in chemicals that specifically influence reporter gene expression (Firmin et al, 1986;Redmond et al, 1986;Djordjevic et al, 1987;Peters and Long, 1988). Because this region of intense activity corresponds with some precision to the region where border cells are released, it was of interest to test the hypothesis that border cells constitute one cellular source of signals that induce microbial gene expression.…”

Section: Discussionmentioning

confidence: 99%

“…Even allowing for loss of some root tip exudate by diffusion into the agar or absorption into paper, the amount from border cells alone could easily account for a significant part of the intense reporter gene activity that occurs at root tips of legumes (Firmin et al, 1986;Redmond et al, 1986;Djordjevic et al, 1987;Peters and Long, 1988).…”

Section: Discussionmentioning

confidence: 99%

“…Conditions of the plate assay used in previous studies (Firmin et al, 1986;Redmond et al, 1986;Djordjevic et al, 1987;Peters and Long, 1988)-incubation of plant roots with bacteria overnight at 28°C-were duplicated, but in the current study the only source of chemicals was border cells. A quantitative assay was used to measure enzyme activity reflecting the level of the reporter gene product present at the end of the cocultivation period.…”

Section: Species-dependent Variation In Lnduction Of Reporter Cene Exmentioning

confidence: 99%

“…(Firmin et al, 1986;Redmond et al, 1986;Djordjevic et al, 1987;Peters and Long, 1988). In those studies a plate assay in which host plants were cocultivated overnight at 28°C with Rkizobium strains was used (Djordjevic et al, 1987;Peters and Long, 1988).…”

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Induction of Microbial Genes for Pathogenesis and Symbiosis by Chemicals from Root Border Cells

1997

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Reporter strains of soil-borne bacteria were used to test the hypothesis that chemicals released by root border cells can influente the expression of bacterial genes required for the establishment of plant-microbe associations. Promoters from genes known to be activated by plant factors included vir€, required for Agrobacferium fumefaciens pathogenesis, and common nod genes from Rhizobium leguminosarum bv viciae and Rhizobium melilofi, required for nodulation of pea (Pisum sativum) and alfalfa (Medicago safivum), respectively. Also included was phzB, an autoinducible gene encoding the biosynthesis of antibiotics by Pseudomonas aureofaciens. The vir€ and nod genes were activated to different degrees, depending on the source of border cells, whereas phzB activity remained unaffected. The homologous interaction between R. leguminosarum bv viciae and its host, pea, was examined in

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Mass spectrometric analysis of lipo-chitin oligosaccharides-Signal molecules mediating the host-specific legume-rhizobium symbiosis

Drift

Olsthoorn

Brull

et al. 1998

Mass Spectrom. Rev.

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Flavones induce expression of nodulation genes in Rhizobium

Cited by 474 publications

References 18 publications

Concurrent Synthesis and Release of nod-Gene-Inducing Flavonoids from Alfalfa Roots

Concurrent Synthesis and Release of nod-Gene-Inducing Flavonoids from Alfalfa Roots

Induction of Microbial Genes for Pathogenesis and Symbiosis by Chemicals from Root Border Cells

Mass spectrometric analysis of lipo-chitin oligosaccharides-Signal molecules mediating the host-specific legume-rhizobium symbiosis

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