Comparison of the symbiotic and competition phenotypes of<i>Sinorhizobium meliloti</i>PHB synthesis and degradation pathway mutants

Aneja, Punita; Zachertowska, Alicja; Charles, Trevor C.

doi:10.1139/w05-042

Cited by 29 publications

(28 citation statements)

References 20 publications

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“…Because the role of PHA in nitrogen fixation in different rhizobia is controversial (38)(39)(40) and there are no data available for B. japonicum, we decided to investigate whether the lack of PHA or excess PHA affects the accumulation of dry mass in soybean plants cultured in an N-free plant nutrient solution.…”

Section: Resultsmentioning

confidence: 99%

Analysis of Two Polyhydroxyalkanoate Synthases in Bradyrhizobium japonicum USDA 110

Quelas

Mongiardini

Pérez-Giménez

et al. 2013

Journal of Bacteriology

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bBradyrhizobium japonicum USDA 110 has five polyhydroxyalkanoate (PHA) synthases (PhaC) annotated in its genome: bll4360 (phaC1), bll6073 (phaC2), blr3732 (phaC3), blr2885 (phaC4), and bll4548 (phaC5). All these proteins possess the catalytic triad and conserved amino acid residues of polyester synthases and are distributed into four different PhaC classes. We obtained mutants in each of these paralogs and analyzed phaC gene expression and PHA production in liquid cultures. Despite the genetic redundancy, only phaC1 and phaC2 were expressed at significant rates, while PHA accumulation in stationary-phase cultures was impaired only in the ⌬phaC1 mutant. Meanwhile, the ⌬phaC2 mutant produced more PHA than the wild type under this condition, and surprisingly, the phaC3 transcript increased in the ⌬phaC2 background. A double mutant, the ⌬phaC2 ⌬phaC3 mutant, consistently accumulated less PHA than the ⌬phaC2 mutant. PHA accumulation in nodule bacteroids followed a pattern similar to that seen in liquid cultures, being prevented in the ⌬phaC1 mutant and increased in the ⌬phaC2 mutant in relation to the level in the wild type. Therefore, we used these mutants, together with a ⌬phaC1 ⌬phaC2 double mutant, to study the B. japonicum PHA requirements for survival, competition for nodulation, and plant growth promotion. All mutants, as well as the wild type, survived for 60 days in a carbon-free medium, regardless of their initial PHA contents. When competing for nodulation against the wild type in a 1:1 proportion, the ⌬phaC1 and ⌬phaC1 ⌬phaC2 mutants occupied only 13 to 15% of the nodules, while the ⌬phaC2 mutant occupied 81%, suggesting that the PHA polymer is required for successful competitiveness. However, the bacteroid content of PHA did not affect the shoot dry weight accumulation.

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Section: Resultsmentioning

confidence: 99%

Analysis of Two Polyhydroxyalkanoate Synthases in Bradyrhizobium japonicum USDA 110

Quelas

Mongiardini

Pérez-Giménez

et al. 2013

Journal of Bacteriology

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“…A number of mutations that affect competition for nodule occupancy have been reported in the literature (Aneja et al, 2005;Fry et al, 2001;Jiménez-Zurdo et al, 1995;Oresnik et al, 1998;Phillips et al, 1998;Rosenblueth et al, 1998;Soedarjo & Borthakur, 1998;Streit et al, 1996). The magnitude of these phenotypes appears to vary from severe to statistically significant but subtle.…”

Section: Discussionmentioning

confidence: 99%

Sinorhizobium meliloti pSymB carries genes necessary for arabinose transport and catabolism

et al. 2007

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Arabinose is a known component of plant cell walls and is found in the rhizosphere. In this work, a previously undeleted region of the megaplasmid pSymB was identified as encoding genes necessary for arabinose catabolism, by Tn5-B20 random mutagenesis and subsequent complementation. Transcription of this region was measured by b-galactosidase assays of Tn5-B20 fusions, and shown to be strongly inducible by arabinose, and moderately so by galactose and seed exudate. Accumulation of [ 3 H]arabinose in mutants and wild-type was measured, and the results suggested that this operon is necessary for arabinose transport. Although catabolite repression of the arabinose genes by succinate or glucose was not detected at the level of transcription, both glucose and galactose were found to inhibit accumulation of arabinose when present in excess. To determine if glucose was also taken up by the arabinose transport proteins, [ 14 C]glucose uptake rates were measured in wild-type and arabinose mutant strains. No differences in glucose uptake rates were detected between wild-type and arabinose catabolism mutant strains, indicating that excess glucose did not compete with arabinose for transport by the same system. Arabinose mutants were tested for the ability to form nitrogen-fixing nodules on alfalfa, and to compete with the wild-type for nodule occupancy. Strains unable to utilize arabinose did not display any symbiotic defects, and were not found to be less competitive than wild-type for nodule occupancy in co-inoculation experiments. Moreover, the results suggest that other loci are required for arabinose catabolism, including a gene encoding arabinose dehydrogenase.

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“…Polyhydroxybutyrate (PHB) granules, produced by S. meliloti during the invasion process, are degraded during bacteroid differentiation and appear to be used preferentially as a carbon source at this stage 109 . Surprisingly, mutants in PHB synthesis (phbC) or degradation (bdhA) are symbiotically competent, indicating that alternate carbon sources are available to the bacteria during differentiation [109][110][111] . In a mixed infection, phbC and bdhA mutants are less competitive for nodule occupancy than the wild type, suggesting that the ability to synthesize and use PHB might allow the bacteria to compete in situations of reduced carbon availability 109,111 .…”

Section: Nih-pa Author Manuscriptmentioning

confidence: 99%

“…Surprisingly, mutants in PHB synthesis (phbC) or degradation (bdhA) are symbiotically competent, indicating that alternate carbon sources are available to the bacteria during differentiation [109][110][111] . In a mixed infection, phbC and bdhA mutants are less competitive for nodule occupancy than the wild type, suggesting that the ability to synthesize and use PHB might allow the bacteria to compete in situations of reduced carbon availability 109,111 . Fixed carbon from the plant is provided to the bacteria in the form of dicarboxylic acids, such as malate, through the bacterial Dct uptake system 101,112 .…”

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confidence: 99%

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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Comparison of the symbiotic and competition phenotypes ofSinorhizobium melilotiPHB synthesis and degradation pathway mutants

Cited by 29 publications

References 20 publications

Analysis of Two Polyhydroxyalkanoate Synthases in Bradyrhizobium japonicum USDA 110

Analysis of Two Polyhydroxyalkanoate Synthases in Bradyrhizobium japonicum USDA 110

Sinorhizobium meliloti pSymB carries genes necessary for arabinose transport and catabolism

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

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