Diverse Flavonoids Stimulate NodD1 Binding to<i>nod</i>Gene Promoters in<i>Sinorhizobium meliloti</i>

Peck, Melicent C.; Fisher, Robert F.; Long, Sharon R.

doi:10.1128/jb.00376-06

Cited by 189 publications

(156 citation statements)

References 79 publications

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“…Flavonoids bind bacterial NodD proteins, which are members of the LysR family of transcriptional regulators, and activate these proteins to induce the transcription of rhizobial genes 1,2 . For example, the M. sativa-derived flavonoid luteolin stimulates binding of an active form of NodD1 to an S. meliloti 'nod-box' promoter, which activates transcription of the downstream nod genes 3 . S. meliloti has two other NodD proteins -NodD2, which is activated by as-yetunpurified plant compounds, and NodD3, which does not require plant-derived compounds to activate gene expression from nod box promoters 1 .…”

Section: Initial Signal Exchangementioning

confidence: 99%

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How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

et al. 2007

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Nitrogen-fixing rhizobial bacteria and leguminous plants have evolved complex signal exchange mechanisms that allow a specific bacterial species to induce its host plant to form invasion structures through which the bacteria can enter the plant root. Once the bacteria have been endocytosed within a host-membrane-bound compartment by root cells, the bacteria differentiate into a new form that can convert atmospheric nitrogen into ammonia. Bacterial differentiation and nitrogen fixation are dependent on the microaerobic environment and other support factors provided by the plant. In return, the plant receives nitrogen from the bacteria, which allows it to grow in the absence of an external nitrogen source. Here, we review recent discoveries about the mutual recognition process that allows the model rhizobial symbiont Sinorhizobium meliloti to invade and differentiate inside its host plant alfalfa (Medicago sativa) and the model host plant barrel medic (Medicago truncatula).The recent completion of the Sinorhizobium meliloti genome sequence, and the progress towards the completion of the Medicago truncatula genome sequence, have led to a surge in the molecular characterization of the determinants that are involved in the development of the symbiosis between rhizobial bacteria and leguminous plants. Aromatic compounds from legumes called flavonoids first signal the rhizobial bacteria to produce lipochitooligosaccharide compounds called Nod factors 1 . Nod factors that are secreted by the bacteria activate multiple responses in the host plant that prepare the plant to receive the invading bacteria. Nod factors and symbiotic exopolysaccharides induce the plant to form infection threads, which are thin tubules filled with bacteria that penetrate into the plant cortical tissue and deliver the bacteria to their target cells. Plant cells in the inner cortex internalize the invading bacteria in host-membrane-bound compartments that mature into structures known Correspondence to G.C.W. gwalker@mit.edu. Competing interests statementThe authors declare no competing financial interests. DATABASES Invasion of plant rootsAlthough plant roots are exposed to various micro-organisms in the soil, their cell walls form a strong protective barrier against most harmful species. The early steps in the invasion of barrel medic (M. truncatula) and alfalfa (Medicago sativa) roots by S. meliloti are characterized by the reciprocal exchange of signals that allow the bacteria to use the plant root hair cells as a means of entry. Initial signal exchangeFlavonoid compounds (2-phenyl-1,4-benzopyrone derivatives) produced by leguminous plants are the first signals to be exchanged by host-rhizobial symbiont pairs 1 (FIG. 1). Flavonoids bind bacterial NodD proteins, which are members of the LysR family of transcriptional regulators, and activate these proteins to induce the transcription of rhizobial genes 1,2 . For example, the M. sativa-derived flavonoid luteolin stimulates binding of an active form of NodD1 to an S. meliloti 'nod-box' p...

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Section: Initial Signal Exchangementioning

confidence: 99%

“…Any of these NodD proteins can provide S. meliloti with the ability to nodulate M. sativa 1 . Flavonoids from non-host plants can inhibit the transcription of S. meliloti nod genes 3 .…”

Section: Initial Signal Exchangementioning

confidence: 99%

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

et al. 2007

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“…Each species of Rhiz interacts only with a particular subset of host plant species. For example, the soil bacterium Sinorhizobium meliloti will form a symbiotic partnership with its host plant, alfalfa, but not with other legumes such as soybean or clover (19,20). To establish host specificity, alfalfa exudes a unique mixture of flavonoid (luteolin and apigenin) phytochemical signals into the soil, which serve dual functions, to recruit S. meliloti and to inhibit or antagonize nonfavorable species of Rhiz (21)(22)(23).…”

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confidence: 99%

Pesticides reduce symbiotic efficiency of nitrogen-fixing rhizobia and host plants

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Gulledge

Engelhaupt

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

265

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Unprecedented agricultural intensification and increased crop yield will be necessary to feed the burgeoning world population, whose global food demand is projected to double in the next 50 years. Although grain production has doubled in the past four decades, largely because of the widespread use of synthetic nitrogenous fertilizers, pesticides, and irrigation promoted by the ''Green Revolution,'' this rate of increased agricultural output is unsustainable because of declining crop yields and environmental impacts of modern agricultural practices. The last 20 years have seen diminishing returns in crop yield in response to increased application of fertilizers, which cannot be completely explained by current ecological models. A common strategy to reduce dependence on nitrogenous fertilizers is the production of leguminous crops, which fix atmospheric nitrogen via symbiosis with nitrogenfixing rhizobia bacteria, in rotation with nonleguminous crops. Here we show previously undescribed in vivo evidence that a subset of organochlorine pesticides, agrichemicals, and environmental contaminants induces a symbiotic phenotype of inhibited or delayed recruitment of rhizobia bacteria to host plant roots, fewer root nodules produced, lower rates of nitrogenase activity, and a reduction in overall plant yield at time of harvest. The environmental consequences of synthetic chemicals compromising symbiotic nitrogen fixation are increased dependence on synthetic nitrogenous fertilizer, reduced soil fertility, and unsustainable long-term crop yields.legume ͉ nitrogen fixation ͉ symbiosis ͉ Sinorhizobium meliloti

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“…However, it is possible that the increased levels of the two isoflavones, daidzein and formononetin, also play a role in the increased nodule number phenotype. Daidzein stimulates the DNAbinding activity of NodD1 to nod gene promoters of S. meliloti (Peck et al, 2006). Moreover, nodulation in isoflavone-deficient soybean (Glycine max) roots can be restored by using genistein-hypersensitive rhizobial cells, independent of auxin transport restoration, suggesting that induction of nod signal biosynthesis by isoflavones is a critical component of the nodulation signaling mechanism (Subramanian et al, 2006).…”

Section: Discussion Nodulation In Roots Of Reduced-lignin Alfalfa Plantsmentioning

confidence: 90%

Lignin Modification Leads to Increased Nodule Numbers in Alfalfa

et al. 2014

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Reduction of lignin levels in the forage legume alfalfa (Medicago sativa) by down-regulation of the monolignol biosynthetic enzyme hydroxycinnamoyl coenzyme A:shikimate hydroxycinnamoyl transferase (HCT) results in strongly increased digestibility and processing ability of lignocellulose. However, these modifications are often also associated with dwarfing and other changes in plant growth. Given the importance of nitrogen fixation for legume growth, we evaluated the impact of constitutively targeted lignin modification on the belowground organs (roots and nodules) of alfalfa plants. HCT downregulated alfalfa plants exhibit a striking reduction in root growth accompanied by an unexpected increase in nodule numbers when grown in the greenhouse or in the field. This phenotype is associated with increased levels of gibberellins and certain flavonoid compounds in roots. Although HCT down-regulation reduced biomass yields in both the greenhouse and field experiments, the impact on the allocation of nitrogen to shoots or roots was minimal. It is unlikely, therefore, that the altered growth phenotype of reduced-lignin alfalfa is a direct result of changes in nodulation or nitrogen fixation efficiency. Furthermore, HCT down-regulation has no measurable effect on carbon allocation to roots in either greenhouse or 3-year field trials.

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Diverse Flavonoids Stimulate NodD1 Binding tonodGene Promoters inSinorhizobium meliloti

Cited by 189 publications

References 79 publications

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

Pesticides reduce symbiotic efficiency of nitrogen-fixing rhizobia and host plants

Lignin Modification Leads to Increased Nodule Numbers in Alfalfa

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