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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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Phenotypes of M. truncatula and M. sativa plants nodulated with S. meliloti IAA or control strain. A. M. truncatula root nodules: nodules induced by S. meliloti IAA strain (bottom) and nodules induced by the S. meliloti control strain (top). B. M. sativa root nodules: nodules induced by the S. meliloti IAA strain (bottom) and nodules induced by S. meliloti control strain (top). C. M. truncatula roots of plants nodulated by the IAA strain (right) and roots of plants nodulated by the control strain (left) D. M. sativa roots of plants nodulated by the IAA strain (right) and roots of plants nodulated by the control strain (left).
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Figure 3: Phenotypes of M. truncatula and M. sativa plants nodulated with S. meliloti IAA or control strain. A. M. truncatula root nodules: nodules induced by S. meliloti IAA strain (bottom) and nodules induced by the S. meliloti control strain (top). B. M. sativa root nodules: nodules induced by the S. meliloti IAA strain (bottom) and nodules induced by S. meliloti control strain (top). C. M. truncatula roots of plants nodulated by the IAA strain (right) and roots of plants nodulated by the control strain (left) D. M. sativa roots of plants nodulated by the IAA strain (right) and roots of plants nodulated by the control strain (left).

Mentions: Root growth, nodule number and shoot growth of plants inoculated with either IAA or control S. meliloti strains were evaluated 40 days after germination. In M. truncatula, the average number of nodules per plant was doubled in plants infected by the IAA strain compared to plants infected with the control strain (Fig. 3A and Fig. 4A).


Auxin and nitric oxide control indeterminate nodule formation.

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

Phenotypes of M. truncatula and M. sativa plants nodulated with S. meliloti IAA or control strain. A. M. truncatula root nodules: nodules induced by S. meliloti IAA strain (bottom) and nodules induced by the S. meliloti control strain (top). B. M. sativa root nodules: nodules induced by the S. meliloti IAA strain (bottom) and nodules induced by S. meliloti control strain (top). C. M. truncatula roots of plants nodulated by the IAA strain (right) and roots of plants nodulated by the control strain (left) D. M. sativa roots of plants nodulated by the IAA strain (right) and roots of plants nodulated by the control strain (left).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Phenotypes of M. truncatula and M. sativa plants nodulated with S. meliloti IAA or control strain. A. M. truncatula root nodules: nodules induced by S. meliloti IAA strain (bottom) and nodules induced by the S. meliloti control strain (top). B. M. sativa root nodules: nodules induced by the S. meliloti IAA strain (bottom) and nodules induced by S. meliloti control strain (top). C. M. truncatula roots of plants nodulated by the IAA strain (right) and roots of plants nodulated by the control strain (left) D. M. sativa roots of plants nodulated by the IAA strain (right) and roots of plants nodulated by the control strain (left).
Mentions: Root growth, nodule number and shoot growth of plants inoculated with either IAA or control S. meliloti strains were evaluated 40 days after germination. In M. truncatula, the average number of nodules per plant was doubled in plants infected by the IAA strain compared to plants infected with the control strain (Fig. 3A and Fig. 4A).

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