Gigaspora margarita with and without its endobacterium shows adaptive responses to oxidative stress

Abstract

Arbuscular mycorrhizal (AM) fungi experience oxidative stress during the plant-fungal interaction, due to endogenous reactive oxygen species (ROS) produced by fungal metabolism and exogenous ROS produced by plant cells. Here, we examine the responses to H2O2 in Gigaspora margarita, an AM fungus containing the endobacterial symbiont Candidatus Glomeribacter gigasporarum (CaGg). Previous studies revealed that G. margarita with its endobacterium produces more ATP and has higher respiratory activity compared to a cured line that lacks the endobacterium. This higher bioenergetic potential leads to higher production of ROS, and to a higher ROS-detoxifying capacity, suggesting a direct or indirect role of the endobacterium in modulating fungal anti-oxidant responses. To test the hypothesis that the fungal-endobacterial symbiosis may enhance the fitness of the AM fungus in the presence of oxidative stress, we treated the fungus with a sublethal concentration of H2O2 and performed RNA-seq analysis. Our results demonstrate that: i) irrespective of the endobacterium presence, G. margarita faces oxidative stress by activating multiple metabolic processes (methionine oxidation, sulfur uptake, the pentose phosphate pathway, activation of ROS-scavenger genes), ii) in the presence of its endobacterium, G. margarita upregulates some metabolic pathways, like chromatin status modifications and iron metabolism; iii) contrary to our hypothesis, the cured line responds to H2O2 by activating the transcription of specific ROS scavengers. We confirmed the RNA-seq findings by measuring the glutathione and ascorbate content, which was the same in both lines after H2O2 treatment. We conclude that both fungal lines

Metabolome changes are induced in the arbuscular mycorrhizal fungus Gigaspora margarita by germination and by its bacterial endosymbiont

“…Glutathione is oxidized to glutathione disulfide (GSSG) when its cysteine groups are exposed to oxidants, and is restored to the reduced form by glutathione reductase. An increase in the transcript levels of glutathione peroxidase, an enzyme which uses glutathione as a substrate to reduce H2O2, was found in G. margarita upon hydrogen peroxide and strigolactone treatment (Salvioli et al 2016;Venice et al 2017). The metabolomics data presented here seems to confirm RNA-seq data.…”

Mycoplasma-related endobacteria within Mortierellomycotina fungi: diversity, distribution and functional insights into their lifestyle

“…Perhaps the most fascinating study describing a function of a bacterial endosymbiont is represented by Burkholderia rhizoxinica, which is responsible of the pathogenicity and its fungal host Rhizopus microsporus [59]. In recent years, several other studies provided novel insights into the lifestyle of fungal endobacteria, mainly Burkholderia-related endobacteria (BRE) [13,[15][16][17][60][61][62][63][64]. Importantly, all these contributions became possible after endobacteria were cleared from their hosts [16,17,65], thus allowing researchers to compare the same fungal strain in presence/ absence of its BRE symbiont.…”

Apple Replant Disease: Causes and Mitigation Strategies

“…realtime PCR quantification of AMF, Alkan et al, 2004, Voříšková et al, 2017; DNA based sequencing for identification and diversity studies of AMF, Vasar et al, 2017) can help to determine fungal communities with positive effects on apple plants. Also, AMF isolates harboring mycoviruses (Ikeda et al, 2012) or endobacteria (Venice et al, 2017) are of interest with regard to their influence on the symbiotic performance of AMF in ARD soil as well as in biocontrol strategies.…”