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Intra and Inter-Spore Variability in Rhizophagus irregularis AOX Gene.

Campos C, Cardoso H, Nogales A, Svensson J, Lopez-Ráez JA, Pozo MJ, Nobre T, Schneider C, Arnholdt-Schmitt B - PLoS ONE (2015)

Bottom Line: Nevertheless, virtually nothing is known on the involvement of AMF AOX on symbiosis establishment, as well on the existence of AOX variability that could affect AMF effectiveness and consequently plant performance.The analysis of RiAOX polymorphisms in single spores of three different isolates showed a reduced variability in one spore relatively to a group of spores.A high number of polymorphisms occurred in introns; nevertheless, some putative amino acid changes resulting from non-synonymous variants were found, offering a basis for selective pressure to occur within the populations.

View Article: PubMed Central - PubMed

Affiliation: EU Marie Curie Chair, ICAAM-Instituto de Ciências Agrárias e Ambientais Mediterrânicas, IIFA-Instituto de Formação e Investigação Avançada, Universidade de Évora, Núcleo da Mitra, Évora, Portugal.

ABSTRACT
Arbuscular mycorrhizal fungi (AMF) are root-inhabiting fungi that form mutualistic symbioses with their host plants. AMF symbiosis improves nutrient uptake and buffers the plant against a diversity of stresses. Rhizophagus irregularis is one of the most widespread AMF species in the world, and its application in agricultural systems for yield improvement has increased over the last years. Still, from the inoculum production perspective, a lack of consistency of inoculum quality is referred to, which partially may be due to a high genetic variability of the fungus. The alternative oxidase (AOX) is an enzyme of the alternative respiratory chain already described in different taxa, including various fungi, which decreases the damage caused by oxidative stress. Nevertheless, virtually nothing is known on the involvement of AMF AOX on symbiosis establishment, as well on the existence of AOX variability that could affect AMF effectiveness and consequently plant performance. Here, we report the isolation and characterisation of the AOX gene of R. irregularis (RiAOX), and show that it is highly expressed during early phases of the symbiosis with plant roots. Phylogenetic analysis clustered RiAOX sequence with ancient fungi, and multiple sequence alignment revealed the lack of several regulatory motifs which are present in plant AOX. The analysis of RiAOX polymorphisms in single spores of three different isolates showed a reduced variability in one spore relatively to a group of spores. A high number of polymorphisms occurred in introns; nevertheless, some putative amino acid changes resulting from non-synonymous variants were found, offering a basis for selective pressure to occur within the populations. Given the AOX relatedness with stress responses, differences in gene variants amongst R. irregularis isolates are likely to be related with its origin and environmental constraints and might have a potential impact on inoculum production.

No MeSH data available.


Related in: MedlinePlus

Expression levels of AOX gene family in mycorrhizal and non-mycorrhizal tomato roots.Expression levels were analysed at 1, 2, 4 and 6 weeks post-inoculation with R. irregularis. The expression levels of SlAOX1a (A), SlAOX1b (B), SlAOX1c (C), SlAOX2 (D) and SlPT4 (E) were analysed in roots of mycorrhizal and non-mycorrhizal tomato plants. The transcript levels of RiAOX were analysed on mycorrhizal roots of tomato (F). Asterisks (*) indicate significant differences (P < 0.05) in expression between mycorrhizal and non-mycorrhizal roots at one time point. Different superscript letters (a, b) indicate significant differences (P < 0.05) between weeks on mycorrhizal roots. No expression of SlPT4 and RiAOX was found in non-mycorrhizal roots.
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pone.0142339.g004: Expression levels of AOX gene family in mycorrhizal and non-mycorrhizal tomato roots.Expression levels were analysed at 1, 2, 4 and 6 weeks post-inoculation with R. irregularis. The expression levels of SlAOX1a (A), SlAOX1b (B), SlAOX1c (C), SlAOX2 (D) and SlPT4 (E) were analysed in roots of mycorrhizal and non-mycorrhizal tomato plants. The transcript levels of RiAOX were analysed on mycorrhizal roots of tomato (F). Asterisks (*) indicate significant differences (P < 0.05) in expression between mycorrhizal and non-mycorrhizal roots at one time point. Different superscript letters (a, b) indicate significant differences (P < 0.05) between weeks on mycorrhizal roots. No expression of SlPT4 and RiAOX was found in non-mycorrhizal roots.

Mentions: The gene expression analysis revealed that tomato AOX genes were stable during the first two weeks of the experiment, although mycorrhizal colonisation was already visible one week post-inoculation (S2 Table). At four weeks post-inoculation, two genes were up-regulated by mycorrhization with R. irregularis (Fig 4): SlAOX1a and SlAOX1c gene transcript levels increased (Fig 4A and 4C), coinciding with the appearing of the first arbuscules and vesicules (S2 Table). By 6 weeks post-inoculation, when more than a half of the roots were colonized by the AMF (S2 Table), SlAOX1a and SlAOX1c transcript accumulation was significantly higher in mycorrhizal plant roots (Fig 4A and 4C) (P < 0.05), and a similar trend was found for SlAOX1b despite the non-significant results (Fig 4B). Non-significant differences were observed for SlAOX2 along the entire experiment (Fig 4C). The expression of SlAOX genes in non-mycorrhizal plant roots remained stable during the 6 weeks of the trial. The tomato phosphate transporter SlPT4 was 14.5 fold up-regulated between 1 and 6 weeks post-inoculation with R. irregularis (P < 0.001) (Fig 4E).


Intra and Inter-Spore Variability in Rhizophagus irregularis AOX Gene.

Campos C, Cardoso H, Nogales A, Svensson J, Lopez-Ráez JA, Pozo MJ, Nobre T, Schneider C, Arnholdt-Schmitt B - PLoS ONE (2015)

Expression levels of AOX gene family in mycorrhizal and non-mycorrhizal tomato roots.Expression levels were analysed at 1, 2, 4 and 6 weeks post-inoculation with R. irregularis. The expression levels of SlAOX1a (A), SlAOX1b (B), SlAOX1c (C), SlAOX2 (D) and SlPT4 (E) were analysed in roots of mycorrhizal and non-mycorrhizal tomato plants. The transcript levels of RiAOX were analysed on mycorrhizal roots of tomato (F). Asterisks (*) indicate significant differences (P < 0.05) in expression between mycorrhizal and non-mycorrhizal roots at one time point. Different superscript letters (a, b) indicate significant differences (P < 0.05) between weeks on mycorrhizal roots. No expression of SlPT4 and RiAOX was found in non-mycorrhizal roots.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4634980&req=5

pone.0142339.g004: Expression levels of AOX gene family in mycorrhizal and non-mycorrhizal tomato roots.Expression levels were analysed at 1, 2, 4 and 6 weeks post-inoculation with R. irregularis. The expression levels of SlAOX1a (A), SlAOX1b (B), SlAOX1c (C), SlAOX2 (D) and SlPT4 (E) were analysed in roots of mycorrhizal and non-mycorrhizal tomato plants. The transcript levels of RiAOX were analysed on mycorrhizal roots of tomato (F). Asterisks (*) indicate significant differences (P < 0.05) in expression between mycorrhizal and non-mycorrhizal roots at one time point. Different superscript letters (a, b) indicate significant differences (P < 0.05) between weeks on mycorrhizal roots. No expression of SlPT4 and RiAOX was found in non-mycorrhizal roots.
Mentions: The gene expression analysis revealed that tomato AOX genes were stable during the first two weeks of the experiment, although mycorrhizal colonisation was already visible one week post-inoculation (S2 Table). At four weeks post-inoculation, two genes were up-regulated by mycorrhization with R. irregularis (Fig 4): SlAOX1a and SlAOX1c gene transcript levels increased (Fig 4A and 4C), coinciding with the appearing of the first arbuscules and vesicules (S2 Table). By 6 weeks post-inoculation, when more than a half of the roots were colonized by the AMF (S2 Table), SlAOX1a and SlAOX1c transcript accumulation was significantly higher in mycorrhizal plant roots (Fig 4A and 4C) (P < 0.05), and a similar trend was found for SlAOX1b despite the non-significant results (Fig 4B). Non-significant differences were observed for SlAOX2 along the entire experiment (Fig 4C). The expression of SlAOX genes in non-mycorrhizal plant roots remained stable during the 6 weeks of the trial. The tomato phosphate transporter SlPT4 was 14.5 fold up-regulated between 1 and 6 weeks post-inoculation with R. irregularis (P < 0.001) (Fig 4E).

Bottom Line: Nevertheless, virtually nothing is known on the involvement of AMF AOX on symbiosis establishment, as well on the existence of AOX variability that could affect AMF effectiveness and consequently plant performance.The analysis of RiAOX polymorphisms in single spores of three different isolates showed a reduced variability in one spore relatively to a group of spores.A high number of polymorphisms occurred in introns; nevertheless, some putative amino acid changes resulting from non-synonymous variants were found, offering a basis for selective pressure to occur within the populations.

View Article: PubMed Central - PubMed

Affiliation: EU Marie Curie Chair, ICAAM-Instituto de Ciências Agrárias e Ambientais Mediterrânicas, IIFA-Instituto de Formação e Investigação Avançada, Universidade de Évora, Núcleo da Mitra, Évora, Portugal.

ABSTRACT
Arbuscular mycorrhizal fungi (AMF) are root-inhabiting fungi that form mutualistic symbioses with their host plants. AMF symbiosis improves nutrient uptake and buffers the plant against a diversity of stresses. Rhizophagus irregularis is one of the most widespread AMF species in the world, and its application in agricultural systems for yield improvement has increased over the last years. Still, from the inoculum production perspective, a lack of consistency of inoculum quality is referred to, which partially may be due to a high genetic variability of the fungus. The alternative oxidase (AOX) is an enzyme of the alternative respiratory chain already described in different taxa, including various fungi, which decreases the damage caused by oxidative stress. Nevertheless, virtually nothing is known on the involvement of AMF AOX on symbiosis establishment, as well on the existence of AOX variability that could affect AMF effectiveness and consequently plant performance. Here, we report the isolation and characterisation of the AOX gene of R. irregularis (RiAOX), and show that it is highly expressed during early phases of the symbiosis with plant roots. Phylogenetic analysis clustered RiAOX sequence with ancient fungi, and multiple sequence alignment revealed the lack of several regulatory motifs which are present in plant AOX. The analysis of RiAOX polymorphisms in single spores of three different isolates showed a reduced variability in one spore relatively to a group of spores. A high number of polymorphisms occurred in introns; nevertheless, some putative amino acid changes resulting from non-synonymous variants were found, offering a basis for selective pressure to occur within the populations. Given the AOX relatedness with stress responses, differences in gene variants amongst R. irregularis isolates are likely to be related with its origin and environmental constraints and might have a potential impact on inoculum production.

No MeSH data available.


Related in: MedlinePlus