Legume Signals to Rhizobial Symbionts: A New Approach for Defining Rhizosphere Colonization

Phillips, Donald A.; Streit, Wolfgang R.

doi:10.1007/978-1-4613-1213-0_7

Cited by 28 publications

(14 citation statements)

References 141 publications

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“…In our previous report (13), based on the presence of two octapeptide repeats in the primary structure of BGAF, we had proposed that BGAF was monomeric and bivalent and each bivalent monomer bound to two ␤-glucosidase dimers, linking ␤-glucosidase dimers in a linear chain in which monomeric BGAF with two binding sites and dimeric ␤-glucosidase alternate. Our present studies on BGAF and the results from mapping of amino acid residues on maize Glu1 involved in BGAF binding by site-directed mutagenesis 3 do not support the involvement of the two octapeptide repeats in BGAF in ␤-glucosidase binding. The present consensus is that native BGAF is a homodimer with one ␤-glucosidase binding site per monomer (in the JRL domain).…”

Section: Discussioncontrasting

confidence: 98%

“…bind maize Glu1. 3 If the JRL domain of maize BGAF is solely responsible for ␤-glucosidase aggregation, we hypothesized that replacing the JRL domain of BGAF homolog from sorghum with that of maize would confer ␤-glucosidase binding and aggregating activity to it. To this end, we constructed Sbdirigent-ZmJRL chimera, expressed it in E. coli, and tested it for ␤-glucosidase binding and aggregating activity.…”

Section: Table 3 Inhibition Of Hemagglutination Activity Of Native Bgmentioning

confidence: 99%

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Maize β-Glucosidase-aggregating Factor Is a Polyspecific Jacalin-related Chimeric Lectin, and Its Lectin Domain Is Responsible for β-Glucosidase Aggregation

Kittur¹,

Lalgondar²,

Yu³

et al. 2007

Journal of Biological Chemistry

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In certain maize genotypes, called "null," ␤-glucosidase does not enter gels and therefore cannot be detected on zymograms after electrophoresis. Such genotypes were originally thought to be homozygous for a null allele at the glu1 gene and thus devoid of enzyme. We have shown that a ␤-glucosidase-aggregating factor (BGAF) is responsible for the "null" phenotype. BGAF is a chimeric protein consisting of two distinct domains: the disease response or "dirigent" domain and the jacalin-related lectin (JRL) domain. First, it was not known whether the lectin domain in BGAF is functional. Second, it was not known which of the two BGAF domains is involved in ␤-glucosidase binding and aggregation. To this end, we purified BGAF to homogeneity from a maize null inbred line called H95. The purified protein gave a single band on SDS-PAGE, and the native protein was a homodimer of 32-kDa monomers. Native and recombinant BGAF (produced in Escherichia coli) agglutinated rabbit erythrocytes, and various carbohydrates and glycoproteins inhibited their hemagglutination activity. Sugars did not have any effect on the binding of BGAF to the ␤-glucosidase isozyme 1 (Glu1), and the BGAF-Glu1 complex could still bind lactosyl-agarose, indicating that the sugar-binding site of BGAF is distinct from the ␤-glucosidase-binding site. Neither the dirigent nor the JRL domains alone (produced separately in E. coli) produced aggregates of Glu1 based on results from pull-down assays. However, gel shift and competitive binding assays indicated that the JRL domain binds ␤-glucosidase without causing it to aggregate. These results with those from deletion mutagenesis and replacement of the JRL domain of a BGAF homolog from sorghum, which does not bind Glu1, with that from maize allowed us to conclude that the JRL domain of BGAF is responsible for its lectin and ␤-glucosidase binding and aggregating activities.␤-Glucosidases (␤-D-glucoside glucohydrolase; EC 3.2.1.21) hydrolyze ␤-glycosidic linkage(s) in alkyl and aryl ␤-D-glucosides, glycoproteins, and glycolipids and that between two glucose residues in ␤-linked oligosaccharides. They are found in all three (Archaea, Eubacteria, and Eukarya) domains of liv-

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Section: Discussioncontrasting

confidence: 98%

Section: Table 3 Inhibition Of Hemagglutination Activity Of Native Bgmentioning

confidence: 99%

Maize β-Glucosidase-aggregating Factor Is a Polyspecific Jacalin-related Chimeric Lectin, and Its Lectin Domain Is Responsible for β-Glucosidase Aggregation

Kittur¹,

Lalgondar²,

Yu³

et al. 2007

Journal of Biological Chemistry

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“…Indeed, a significant increase in counts of PAH-degrading bacteria was observed in the planted treatment inoculated with Rhizobium after 90 days and this may have resulted in substantial degradation of PAHs in the soil. Previous studies have indicated that rhizobia can increase exudation from host plant roots and secondary plant metabolites such as luteolin (a plant flavone) may serve to control nodABC expression during nodule development [53,54]. Thus, increased amounts of exudates may in turn support the growth of microbial degraders or influence pollutant availability.…”

Section: Discussionmentioning

confidence: 99%

Influence of Rhizobium meliloti on phytoremediation of polycyclic aromatic hydrocarbons by alfalfa in an aged contaminated soil

Teng

Shen

Luo

et al. 2011

Journal of Hazardous Materials

151

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“…Almost all constituents of a plant can make their way into the rhizosphere at some time or other (112). Exudates from living roots include amino acids, CO 2 , hormones (including ethylene), organic acids, phenolic substances, sugars, vitamins, etc., as well as polysaccharides and proteins (particularly enzymes) (73,74). Among other roles, this carbon efflux attracts organisms (both mutualistic and pathogenic) towards the roots.…”

Section: Legume Bowers Are Decorated With Flavonoidsmentioning

confidence: 99%

Keys to Symbiotic Harmony

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At least three different sets of symbiotic signals (here, they are compared to locks and keys) are exchanged between legumes and rhizobia during nodule development. Flavonoids, the first of these, emanate from the plant and interact with rhizobial NodD proteins that serve as both environmental sensors and activators of transcription. A second set of signals is synthesized when NodD-flavonoid complexes activate transcription from nod boxes. Most of the genes immediately downstream of these promoters are involved in the synthesis of lipooligosaccharidic Nod factors that provoke deformation of root hairs and allow rhizobia to enter the root through infection threads. Fine-tuning of transcription of nodulation (nod) genes is probably related to sequence variations in individual nod boxes (there are 19 on the symbiotic plasmid of the broad-hostrange Rhizobium sp. strain NGR234). Other rhizobial products seem to be necessary for continued infection thread development, and these represent a third set of signals. Among them are extracellular polysaccharides (EPS) and related compounds, as well as proteins exported by the type three secretion system (TTSS). In the latter case, flavonoids also activate protein secretion, suggesting that the same keys can unlock different doors.Symbioses are nearly ubiquitous, and many are also persistent (56). Mutualistic, nitrogen-fixing associations between members of the plant family Leguminosae, and the soil bacteria Azorhizobium, Bradyrhizobium, Mesorhizobium, and Rhizobium (collectively called rhizobia) contribute substantially to plant productivity (111). Legume-Rhizobium symbioses are marriages between two vastly different genomes. In rhizobia, these include a chromosome plus zero to many plasmids, totalling 6 to 9 Mbp (71). In contrast, genomes of legumes are much larger, some comprising more than 20 chromosomes with total DNA contents that range from about 450 to 4,500 Mbp per haploid genome (1C) (1). As examples, the model legumes Lotus japonicus and Medicago truncatula have six or eight chromosomes totalling 450 and 500 Mbp/1C (14), respectively. Common beans (Phaseolus vulgaris) and related species (e.g., Vigna unguiculata) (both genera belong to the tribe Phaseoleae) have 11 chromosomes each (24) with DNA contents of 637 (1) and 540 Mbp/1C (50). Furthermore, several widely cultivated legumes such as Arachis hypogaea, Glycine max, and Medicago sativa are effectively polyploid, although in G. max most loci segregate as if they were diploid. Legume genomes are thus at least 50 times larger than those of their microsymbionts. Given this disparity, it is difficult to imagine that theirs is a marriage of equals. Nevertheless, their respective contributions are probably not vastly different (see reference 48). LEGUME BOWERS ARE DECORATED WITH FLAVONOIDSWhich partner initiates contact? Since plants are nonmotile, it is tempting to think that courtship begins when bacteria advance into the legume rhizosphere. Yet chemotaxis and motility among rhizobia are clearly not essential for no...

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Legume Signals to Rhizobial Symbionts: A New Approach for Defining Rhizosphere Colonization

Cited by 28 publications

References 141 publications

Maize β-Glucosidase-aggregating Factor Is a Polyspecific Jacalin-related Chimeric Lectin, and Its Lectin Domain Is Responsible for β-Glucosidase Aggregation

Maize β-Glucosidase-aggregating Factor Is a Polyspecific Jacalin-related Chimeric Lectin, and Its Lectin Domain Is Responsible for β-Glucosidase Aggregation

Influence of Rhizobium meliloti on phytoremediation of polycyclic aromatic hydrocarbons by alfalfa in an aged contaminated soil

Keys to Symbiotic Harmony

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