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The plant growth-promoting bacteria Azospirillum amazonense: genomic versatility and phytohormone pathway.

Cecagno R, Fritsch TE, Schrank IS - Biomed Res Int (2015)

Bottom Line: We performed an in silico comparative genomic analysis to understand the genomic plasticity of A. amazonense.Moreover, the presence of the coding sequence for nitrilase indicates the presence of the alternative route that uses IAN as an intermediate for auxin synthesis, but it remains to be established whether the IAN pathway is the Trp-independent route.Future investigations are necessary to support the hypothesis that its genomic structure has evolved to meet the requirement for adaptation to the rhizosphere and interaction with host plants.

View Article: PubMed Central - PubMed

Affiliation: Centro de Biotecnologia, Laboratório de Microrganismos Diazotróficos, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil.

ABSTRACT
The rhizosphere bacterium Azospirillum amazonense associates with plant roots to promote plant growth. Variation in replicon numbers and rearrangements is common among Azospirillum strains, and characterization of these naturally occurring differences can improve our understanding of genome evolution. We performed an in silico comparative genomic analysis to understand the genomic plasticity of A. amazonense. The number of A. amazonense-specific coding sequences was similar when compared with the six closely related bacteria regarding belonging or not to the Azospirillum genus. Our results suggest that the versatile gene repertoire found in A. amazonense genome could have been acquired from distantly related bacteria from horizontal transfer. Furthermore, the identification of coding sequence related to phytohormone production, such as flavin-monooxygenase and aldehyde oxidase, is likely to represent the tryptophan-dependent TAM pathway for auxin production in this bacterium. Moreover, the presence of the coding sequence for nitrilase indicates the presence of the alternative route that uses IAN as an intermediate for auxin synthesis, but it remains to be established whether the IAN pathway is the Trp-independent route. Future investigations are necessary to support the hypothesis that its genomic structure has evolved to meet the requirement for adaptation to the rhizosphere and interaction with host plants.

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A. amazonense pathways of IAA biosynthesis. Tryptophan-dependent pathways or tryptophan-independent pathways (starting from indole or indole-3-glycerol phosphate) are indicated based on routes found in plants and bacteria. Enzymes indicated with an asterisk have been identified in A. amazonense, and routes indicated as dotted lines indicated that the precursor of IAN may or may not be tryptophan.
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fig2: A. amazonense pathways of IAA biosynthesis. Tryptophan-dependent pathways or tryptophan-independent pathways (starting from indole or indole-3-glycerol phosphate) are indicated based on routes found in plants and bacteria. Enzymes indicated with an asterisk have been identified in A. amazonense, and routes indicated as dotted lines indicated that the precursor of IAN may or may not be tryptophan.

Mentions: Biosynthetic pathways for IAA have been fully investigated and tryptophan-dependent and Trp-independent routes have been studied [20, 24, 25]. Although genes coding for proteins related to the bacterial common routes IAM (indole-3-acetamide route) and IPyA (indole-3-pyruvic route) was not found in the A. amazonense genome, the identification of flavin-monooxygenase and nitrilase enzymes suggests the presence of the TAM (tryptamine route) and IAN (indole-3-acetamide route) pathways for IAA synthesis in this bacterium (Figure 2). It is well known that nitrilases in plants (maize and Arabidopsis thaliana) and also in Bacillus amyloliquefaciens were shown to hydrolyze indole-3-acetonitrile (IAN) to IAA [25, 26]. Moreover, evidence for the IAN and TAM pathways has been reported in A. brasilense [21].


The plant growth-promoting bacteria Azospirillum amazonense: genomic versatility and phytohormone pathway.

Cecagno R, Fritsch TE, Schrank IS - Biomed Res Int (2015)

A. amazonense pathways of IAA biosynthesis. Tryptophan-dependent pathways or tryptophan-independent pathways (starting from indole or indole-3-glycerol phosphate) are indicated based on routes found in plants and bacteria. Enzymes indicated with an asterisk have been identified in A. amazonense, and routes indicated as dotted lines indicated that the precursor of IAN may or may not be tryptophan.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4383252&req=5

fig2: A. amazonense pathways of IAA biosynthesis. Tryptophan-dependent pathways or tryptophan-independent pathways (starting from indole or indole-3-glycerol phosphate) are indicated based on routes found in plants and bacteria. Enzymes indicated with an asterisk have been identified in A. amazonense, and routes indicated as dotted lines indicated that the precursor of IAN may or may not be tryptophan.
Mentions: Biosynthetic pathways for IAA have been fully investigated and tryptophan-dependent and Trp-independent routes have been studied [20, 24, 25]. Although genes coding for proteins related to the bacterial common routes IAM (indole-3-acetamide route) and IPyA (indole-3-pyruvic route) was not found in the A. amazonense genome, the identification of flavin-monooxygenase and nitrilase enzymes suggests the presence of the TAM (tryptamine route) and IAN (indole-3-acetamide route) pathways for IAA synthesis in this bacterium (Figure 2). It is well known that nitrilases in plants (maize and Arabidopsis thaliana) and also in Bacillus amyloliquefaciens were shown to hydrolyze indole-3-acetonitrile (IAN) to IAA [25, 26]. Moreover, evidence for the IAN and TAM pathways has been reported in A. brasilense [21].

Bottom Line: We performed an in silico comparative genomic analysis to understand the genomic plasticity of A. amazonense.Moreover, the presence of the coding sequence for nitrilase indicates the presence of the alternative route that uses IAN as an intermediate for auxin synthesis, but it remains to be established whether the IAN pathway is the Trp-independent route.Future investigations are necessary to support the hypothesis that its genomic structure has evolved to meet the requirement for adaptation to the rhizosphere and interaction with host plants.

View Article: PubMed Central - PubMed

Affiliation: Centro de Biotecnologia, Laboratório de Microrganismos Diazotróficos, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil.

ABSTRACT
The rhizosphere bacterium Azospirillum amazonense associates with plant roots to promote plant growth. Variation in replicon numbers and rearrangements is common among Azospirillum strains, and characterization of these naturally occurring differences can improve our understanding of genome evolution. We performed an in silico comparative genomic analysis to understand the genomic plasticity of A. amazonense. The number of A. amazonense-specific coding sequences was similar when compared with the six closely related bacteria regarding belonging or not to the Azospirillum genus. Our results suggest that the versatile gene repertoire found in A. amazonense genome could have been acquired from distantly related bacteria from horizontal transfer. Furthermore, the identification of coding sequence related to phytohormone production, such as flavin-monooxygenase and aldehyde oxidase, is likely to represent the tryptophan-dependent TAM pathway for auxin production in this bacterium. Moreover, the presence of the coding sequence for nitrilase indicates the presence of the alternative route that uses IAN as an intermediate for auxin synthesis, but it remains to be established whether the IAN pathway is the Trp-independent route. Future investigations are necessary to support the hypothesis that its genomic structure has evolved to meet the requirement for adaptation to the rhizosphere and interaction with host plants.

Show MeSH