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.
Highlights
The interaction of arbuscular endomycorrhizal fungi (AMF) and terrestrial plants is a highly ancient (~ 450 million years) and successful symbiosis maintained by the vast majority of plant species, including angiosperms, gymnosperms and some genus of bryophytes and pteridophytes [1,2]
We report the isolation and characterisation of the alternative oxidase (AOX) gene in the AMF Rhizophagus irregularis, the most AMF used as inoculant in agriculture, and we show the involvement of RiAOX on symbiosis establishment by measuring the transcript accumulation over time at both host plant and AMF
The comparison of R. irregularis AOX genomic sequence with other fungi revealed a high variability in the gene structure, related with the number of exons/introns and with their sizes (Fig 1)
Summary
The interaction of arbuscular endomycorrhizal fungi (AMF) (phylum Glomeromycota) and terrestrial plants is a highly ancient (~ 450 million years) and successful symbiosis maintained by the vast majority of plant species, including angiosperms, gymnosperms and some genus of bryophytes and pteridophytes [1,2]. Once contact between the symbionts is established, the fungus forms an appressorium on the root surface via which it enters the root forming highly branched structures (arbuscules) inside root cortical cells [2,3] These arbuscules are connected to an extensive network of extra-radical mycelium providing multifunctional actions to the plant, from nutrient uptake to alleviation against a diversity of stresses including soil metal toxicity [4]. AMF spores contain typically hundreds of nuclei [8] and can carry several genetic variants [9] In this sense, the development of a marker, focused on a selected gene, directly linking a sequence motif (identified at genomic level) to phenotypic variation (inoculum quality) could represent a valid approach to be pursued
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.