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Auxin and nitric oxide control indeterminate nodule formation.

Pii Y, Crimi M, Cremonese G, Spena A, Pandolfini T - BMC Plant Biol. (2007)

Bottom Line: IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules.Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia.The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dipartimento Scientifico Tecnologico, University of Verona, Verona, Italy. pii@sci.univr.it

ABSTRACT

Background: Rhizobia symbionts elicit root nodule formation in leguminous plants. Nodule development requires local accumulation of auxin. Both plants and rhizobia synthesise auxin. We have addressed the effects of bacterial auxin (IAA) on nodulation by using Sinorhizobium meliloti and Rhizobium leguminosarum bacteria genetically engineered for increased auxin synthesis.

Results: IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules. Indeterminate legumes (Medicago species) bearing IAA-overproducing nodules showed an enhanced lateral root development, a process known to be regulated by both IAA and nitric oxide (NO). Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia. The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.

Conclusion: The data hereby presented demonstrate that auxin synthesised by rhizobia and nitric oxide positively affect indeterminate nodule formation and, together with the observation of increased expression of an auxin efflux carrier in roots bearing nodules with higher IAA and NO content, support a model of nodule formation that involves auxin transport regulation and NO synthesis.

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Expression of rolAp-iaaMtms2 construct in indeterminate root nodules. A. Schematic drawing of the chimeric operon. Restriction endonuclease sites used for chimeric operon construction are reported. B. Agarose gel electrophoresis of RT-PCR product obtained from total RNA extracted from nodules (lanes 1 and 5) formed by S. meliloti IAA strain in M. truncatula and M. sativa, respectively. Lanes 3 and 7, RT-PCR performed on total RNA extracted from nodules induced by the control strain in M. truncatula and M. sativa, respectively. Lanes 2 and 4, RNA from nodules of M. truncatula induced by IAA and control strain, amplified without reverse transcriptase; lanes 6 and 8, RNA from nodules of M. sativa induced by IAA and control strain, amplified without reverse transcriptase. Lane 9, no-template control. The position of the primers used in RT-PCR analysis is indicated by arrows in the schematic drawing reported in panel A.
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Figure 1: Expression of rolAp-iaaMtms2 construct in indeterminate root nodules. A. Schematic drawing of the chimeric operon. Restriction endonuclease sites used for chimeric operon construction are reported. B. Agarose gel electrophoresis of RT-PCR product obtained from total RNA extracted from nodules (lanes 1 and 5) formed by S. meliloti IAA strain in M. truncatula and M. sativa, respectively. Lanes 3 and 7, RT-PCR performed on total RNA extracted from nodules induced by the control strain in M. truncatula and M. sativa, respectively. Lanes 2 and 4, RNA from nodules of M. truncatula induced by IAA and control strain, amplified without reverse transcriptase; lanes 6 and 8, RNA from nodules of M. sativa induced by IAA and control strain, amplified without reverse transcriptase. Lane 9, no-template control. The position of the primers used in RT-PCR analysis is indicated by arrows in the schematic drawing reported in panel A.

Mentions: In order to increase the auxin biosynthetic capacity of S. meliloti, we engineered a chimeric construct (Fig. 1A) containing the iaaM gene from Pseudomonas syringae pv. savastanoi and the tms2 gene from Agrobacterium tumefaciens as a bicistronic unit under the control of the prokaryotic promoter (promintron) of the rolA gene of Agrobacterium rhizogenes [16,17]. The iaaM gene codes for a tryptophan monoxygenase, which converts tryptophan to indol-3-acetamide (IAM), while the tms2 gene codes for a hydrolase involved in the conversion of IAM to IAA. The 85 bp-long intron of the T-DNA gene rolA has a dual function: it behaves as an intron when the rolA gene is expressed in plant cells and acts as a prokaryotic promoter in free-living rhizobia and in bacteroids inside nodules [16,17].


Auxin and nitric oxide control indeterminate nodule formation.

Pii Y, Crimi M, Cremonese G, Spena A, Pandolfini T - BMC Plant Biol. (2007)

Expression of rolAp-iaaMtms2 construct in indeterminate root nodules. A. Schematic drawing of the chimeric operon. Restriction endonuclease sites used for chimeric operon construction are reported. B. Agarose gel electrophoresis of RT-PCR product obtained from total RNA extracted from nodules (lanes 1 and 5) formed by S. meliloti IAA strain in M. truncatula and M. sativa, respectively. Lanes 3 and 7, RT-PCR performed on total RNA extracted from nodules induced by the control strain in M. truncatula and M. sativa, respectively. Lanes 2 and 4, RNA from nodules of M. truncatula induced by IAA and control strain, amplified without reverse transcriptase; lanes 6 and 8, RNA from nodules of M. sativa induced by IAA and control strain, amplified without reverse transcriptase. Lane 9, no-template control. The position of the primers used in RT-PCR analysis is indicated by arrows in the schematic drawing reported in panel A.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1878477&req=5

Figure 1: Expression of rolAp-iaaMtms2 construct in indeterminate root nodules. A. Schematic drawing of the chimeric operon. Restriction endonuclease sites used for chimeric operon construction are reported. B. Agarose gel electrophoresis of RT-PCR product obtained from total RNA extracted from nodules (lanes 1 and 5) formed by S. meliloti IAA strain in M. truncatula and M. sativa, respectively. Lanes 3 and 7, RT-PCR performed on total RNA extracted from nodules induced by the control strain in M. truncatula and M. sativa, respectively. Lanes 2 and 4, RNA from nodules of M. truncatula induced by IAA and control strain, amplified without reverse transcriptase; lanes 6 and 8, RNA from nodules of M. sativa induced by IAA and control strain, amplified without reverse transcriptase. Lane 9, no-template control. The position of the primers used in RT-PCR analysis is indicated by arrows in the schematic drawing reported in panel A.
Mentions: In order to increase the auxin biosynthetic capacity of S. meliloti, we engineered a chimeric construct (Fig. 1A) containing the iaaM gene from Pseudomonas syringae pv. savastanoi and the tms2 gene from Agrobacterium tumefaciens as a bicistronic unit under the control of the prokaryotic promoter (promintron) of the rolA gene of Agrobacterium rhizogenes [16,17]. The iaaM gene codes for a tryptophan monoxygenase, which converts tryptophan to indol-3-acetamide (IAM), while the tms2 gene codes for a hydrolase involved in the conversion of IAM to IAA. The 85 bp-long intron of the T-DNA gene rolA has a dual function: it behaves as an intron when the rolA gene is expressed in plant cells and acts as a prokaryotic promoter in free-living rhizobia and in bacteroids inside nodules [16,17].

Bottom Line: IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules.Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia.The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dipartimento Scientifico Tecnologico, University of Verona, Verona, Italy. pii@sci.univr.it

ABSTRACT

Background: Rhizobia symbionts elicit root nodule formation in leguminous plants. Nodule development requires local accumulation of auxin. Both plants and rhizobia synthesise auxin. We have addressed the effects of bacterial auxin (IAA) on nodulation by using Sinorhizobium meliloti and Rhizobium leguminosarum bacteria genetically engineered for increased auxin synthesis.

Results: IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules. Indeterminate legumes (Medicago species) bearing IAA-overproducing nodules showed an enhanced lateral root development, a process known to be regulated by both IAA and nitric oxide (NO). Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia. The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.

Conclusion: The data hereby presented demonstrate that auxin synthesised by rhizobia and nitric oxide positively affect indeterminate nodule formation and, together with the observation of increased expression of an auxin efflux carrier in roots bearing nodules with higher IAA and NO content, support a model of nodule formation that involves auxin transport regulation and NO synthesis.

Show MeSH
Related in: MedlinePlus