Intra and Inter-Spore Variability in Rhizophagus irregularis AOX Gene

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.

Symbiosis Specificity of the Preceding Host Plant Can Dominate but Not Obliterate the Association Between Wheat and Its Arbuscular Mycorrhizal Fungal Partners

“… Kamel et al (2017) found that the secretomes of R. irregularis and G. rosea when colonizing host plants differed according to host. Also genes related to stress responses have sequence polymorphisms between different R. irregularis isolates, which are likely to be related to its origin and natural environmental constraints and can have functional consequences for the host plant ( Campos et al, 2015 ). Since disturbance and prior host changed the relative abundances of specific AMF taxa on wheat roots [for instance Acaulospora was highly sensitive to ERM disturbance, consistent with what has been described previously ( Goss et al, 2017 )], it remains to be seen if different AMF can induce changes in patterns of wheat gene expression and if or how this relates to the greater growth observed with O. compressus as previous host.…”

Alternative Oxidase (AOX) Senses Stress Levels to Coordinate Auxin-Induced Reprogramming From Seed Germination to Somatic Embryogenesis—A Role Relevant for Seed Vigor Prediction and Plant Robustness

“…AOX gene diversity is characterized extensively (Costa et al, 2009b; Polidoros et al, 2009; Cardoso et al, 2015; Nobre et al, 2016; Nogales et al, 2016a), and the importance of ecotyping (Costa and Svensson, 2015), epigenetics (Noceda et al, 2015; Costa and Arnholdt-Schmitt, 2017), and new software based on artificial intelligence (Quaresma et al, 2015) for functional marker development was highlighted. Considering the plant–endophyte interaction for functional genomics was stressed in general (Arnholdt-Schmitt et al, 2014; Nogales et al, 2016b), and involvement of AOX from both partners in symbiotic systems is indicated (Campos et al, 2015; Mercy et al, 2017).…”

Unraveling the Initial Plant Hormone Signaling, Metabolic Mechanisms and Plant Defense Triggering the Endomycorrhizal Symbiosis Behavior

“…For this reason, it has been proposed as an important marker for plant acclimatization to stress conditions (Arnholdt-Schmitt et al, 2006; Clifton et al, 2006). Finally, AOX pathway was also proposed to play a role in AM spore dormancy and germination, as well as, AM fungal behavior in planta , influencing both colonization and arbuscules functionality (Besserer et al, 2009; Campos et al, 2015; Mercy et al, 2017).…”