Trigonelline and Stachydrine Released from Alfalfa Seeds Activate NodD2 Protein in <i>Rhizobium meliloti</i>

Phillips, Donald A.; Joseph, Cecillia M.; Maxwell, Carl A.

doi:10.1104/pp.99.4.1526

Cited by 164 publications

(98 citation statements)

References 30 publications

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“…The inducing capacity varies with flavonoids and rhizobia; and in some cases flavonoids may inhibit induction (61,79,196,197,199). Other molecules, such as the betaines and erythronic and tetronic acids, may also act as inducers (90,198).…”

Section: Flavonoids and Regulation Of Nodulation Genesmentioning

confidence: 99%

Molecular Basis of Symbiotic Promiscuity

Perret

Staehelin

Broughton

2000

Microbiol Mol Biol Rev

881

630

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SUMMARY Eukaryotes often form symbioses with microorganisms. Among these, associations between plants and nitrogen-fixing bacteria are responsible for the nitrogen input into various ecological niches. Plants of many different families have evolved the capacity to develop root or stem nodules with diverse genera of soil bacteria. Of these, symbioses between legumes and rhizobia (Azorhizobium, Bradyrhizobium, Mesorhizobium, and Rhizobium) are the most important from an agricultural perspective. Nitrogen-fixing nodules arise when symbiotic rhizobia penetrate their hosts in a strictly controlled and coordinated manner. Molecular codes are exchanged between the symbionts in the rhizosphere to select compatible rhizobia from pathogens. Entry into the plant is restricted to bacteria that have the “keys” to a succession of legume “doors”. Some symbionts intimately associate with many different partners (and are thus promiscuous), while others are more selective and have a narrow host range. For historical reasons, narrow host range has been more intensively investigated than promiscuity. In our view, this has given a false impression of specificity in legume-Rhizobium associations. Rather, we suggest that restricted host ranges are limited to specific niches and represent specialization of widespread and more ancestral promiscuous symbioses. Here we analyze the molecular mechanisms governing symbiotic promiscuity in rhizobia and show that it is controlled by a number of molecular keys.

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Section: Flavonoids and Regulation Of Nodulation Genesmentioning

confidence: 99%

Molecular Basis of Symbiotic Promiscuity

Perret

Staehelin

Broughton

2000

Microbiol Mol Biol Rev

881

630

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“…One-dimensional proton-NMR and FAB-MS analyses were completed under standard conditions (Phillips et al, 1992). All data were compared with previously published values or authentic standards.…”

Section: Lsolation and Ldentification Of Flavonoidsmentioning

confidence: 99%

Suppression of an Isoflavonoid Phytoalexin Defense Response in Mycorrhizal Alfalfa Roots

et al. 1995

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lsoflavonoids and steady-state mRNA levels of phenylalanine ammonia-lyase, chalcone isomerase, and isoflavone reductase were followed during a rapid, nearly synchronous infection of alfalfa (Medicago sativa L.) roots by the vesicular arbuscular fungus Glomus intraradices (Schenck & Smith) to test whether previously indicated suppression of the host defense response is regulated by changes in the steady-state mRNA level. Relative amounts of steadystate phenylalanine ammonia-lyase mRNA in the mycorrhizal roots doubled between d 14 and 18 and then immediately declined by 75% to reach and maintain a value lower than the control roots through d 21. Relative levels of chalcone isomerase mRNA in the inoculated roots increased 6-fold between d 14 and 17 and then decreased rapidly to the control level. lsoflavone reductase mRNA was not induced by mycorrhizal colonization. High-performance liquid chromatography, proton-nuclear magnetic resonance, and fast atom bombardment-mass spectrometry analyses showed consistent increases in formononetin levels and transient increases in medicarpin-3-Oglycoside and formononetin conjugates i n the inoculated roots when colonization began. As colonization increased, levels of formononetin conjugates declined in mycorrhizal roots below those i n uncolonized controls. Medicarpin aglycone, an alfalfa phytoalexin normally associated with pathogenic infections, was not detected at any stage. These findings supply detailed evidente that, during early colonization of plant roots by symbiotic Clomus, defense transcripts are induced and then subsequently suppressed.Plants are exposed in nature to a wide range of potentially pathogenic fungi and bacteria. Microbial plant pathogens do not generally infect a plant successfully, either because the plant is not a host species or because it is resistant to the pathogen (Koes et al., 1994). ln most cases plant resistance is associated with a hypersensitive response that is characterized by rapid, localized chemical defenses and death of plant cells surrounding the infection site (Meier et al., 1993). Most of these responses are regulated at the level of RNA transcription (Collinge and Slusarenko, 1987; Dixon and Lamb, 1990). In such interactions, the pathogens are usually sensitive to plant defense mechanisms. Alfalfa (Medicago sativa) is a host for various funga1 pathogens (Graham et al., 1979) of the isoflavonoid phytoalexin medicarpin may be involved in resistance to these pathogens (Latunde-Dada and Lucas, 1985; Dixon, 1986). The biosynthetic pathway of medicarpin is well defined (Phillips and Kapulnik, 1995), and activity of severa1 enzymes involved is regulated at the level of RNA transcription (Dixon et al., 1992). VA fungi are obligate symbionts that form mycorrhizae with alfalfa roots. Although pathogenic biotrophs generally exhibit a high degree of host specificity, VA fungi show little to none. Indeed, mycorrhizae occur in approximately 80% of a11 plants (Bonfante-Fasolo, 1987), and VA fungi do not induce typical defense responses in host p...

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“…In addition to alfalfa, other Medicago species, such as Medicago truncatula, Medicago littoralis, Medicago rugosa, and Medicago polymorpha, produce Pro betaine with significant genotypic variations (Wood et al, 1991;Naidu et al, 1992). Pro betaine, which is released by alfalfa seeds during germination (Phillips et al, 1995), is an inducer of nodulation (nod) genes in Sinorhizobium meliloti, the alfalfa-symbiotic species (Phillips et al, 1992). Interestingly, S. meliloti transports this betaine by a high-affinity Na 1 -coupled transporter, BetS (Boscari et al, 2002), and via an ABC (ATP-binding cassette) protein-dependent transporter, Hut (Boncompagni et al, 2000).…”

mentioning

confidence: 99%

Proline Betaine Accumulation and Metabolism in Alfalfa Plants under Sodium Chloride Stress. Exploring Its Compartmentalization in Nodules

et al. 2004

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The osmoprotectant Pro betaine is the main betaine identified in alfalfa (Medicago sativa). We have investigated the long-term responses of nodulated alfalfa plants to salt stress, with a particular interest for Pro betaine accumulation, compartmentalization, and metabolism. Exposure of 3-week-old nodulated alfalfa plants to 0.2 m NaCl for 4 weeks was followed by a 10-, 4-, and 8-fold increase in Pro betaine in shoots, roots, and nodules, respectively. Isotope-labeling studies in alfalfa shoots indicate that [14C]Pro betaine was synthesized from l-[14C]Pro. [14C]Pro betaine was efficiently catabolized through sequential demethylations via N-methylPro and Pro. Salt stress had a minor effect on Pro betaine biosynthesis, whereas it strongly reduced Pro betaine turnover. Analysis of Pro betaine and Pro compartmentalization within nodules revealed that 4 weeks of salinization of the host plants induced a strong increase in cytosol and bacteroids. The estimated Pro betaine and Pro concentrations in salt-stressed bacteroids reached 7.4 and 11.8 mm, respectively, compared to only 0.8 mm in control bacteroids. Na+ content in nodule compartments was also enhanced under salinization, leading to a concentration of 14.7 mm in bacteroids. [14C]Pro betaine and [14C]Pro were taken up by purified symbiosomes and free bacteroids. There was no indication of saturable carrier(s), and the rate of uptake was moderately enhanced by salinization. Ultrastructural analysis showed a large peribacteroid space in salt-stressed nodules, suggesting an increased turgor pressure inside the symbiosomes, which might partially be due to an elevated concentration in Pro, Pro betaine, and Na+ in this compartment.

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Trigonelline and Stachydrine Released from Alfalfa Seeds Activate NodD2 Protein in Rhizobium meliloti

Cited by 164 publications

References 30 publications

Molecular Basis of Symbiotic Promiscuity

Molecular Basis of Symbiotic Promiscuity

Suppression of an Isoflavonoid Phytoalexin Defense Response in Mycorrhizal Alfalfa Roots

Proline Betaine Accumulation and Metabolism in Alfalfa Plants under Sodium Chloride Stress. Exploring Its Compartmentalization in Nodules

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