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

## TL;DR

This paper studies genetic variability in the AOX gene of Rhizophagus irregularis, a fungus that helps plants, and finds differences that could affect its effectiveness in agriculture.

## Contribution

The study isolates and characterizes the AOX gene in Rhizophagus irregularis, revealing its expression patterns and genetic variability across spores.

## Key findings

- The RiAOX gene is highly expressed during early stages of symbiosis with plant roots.
- Phylogenetic analysis shows RiAOX clusters with ancient fungi and lacks regulatory motifs found in plant AOX.
- Genetic variability in RiAOX is observed, with some spores showing fewer polymorphisms and potential amino acid changes.

## 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.