Abstract
Soil water deficit seriously affects crop production, and soil arbuscular mycorrhizal fungi (AMF) enhance drought tolerance in crops by unclear mechanisms. Our study aimed to analyze changes in non-targeted metabolomics in roots of trifoliate orange (Poncirus trifoliata) seedlings under well-watered and soil drought after inoculation with Rhizophagus intraradices, with a focus on terpenoid profile. Root mycorrhizal fungal colonization varied from 70% under soil drought to 85% under soil well-watered, and shoot and root biomass was increased by AMF inoculation, independent of soil water regimes. A total of 643 secondary metabolites in roots were examined, and 210 and 105 differential metabolites were regulated by mycorrhizal fungi under normal water and drought stress, along with 88 and 17 metabolites being up-and down-regulated under drought conditions, respectively. KEGG annotation analysis of differential metabolites showed 38 and 36 metabolic pathways by mycorrhizal inoculation under normal water and drought stress conditions, respectively. Among them, 33 metabolic pathways for mycorrhization under drought stress included purine metabolism, pyrimidine metabolism, alanine, aspartate and glutamate metabolism, etc. We also identified 10 terpenoid substances, namely albiflorin, artemisinin (−)-camphor, capsanthin, β-caryophyllene, limonin, phytol, roseoside, sweroside, and α-terpineol. AMF colonization triggered the decline of almost all differential terpenoids, except for β-caryophyllene, which was up-regulated by mycorrhizas under drought, suggesting potential increase in volatile organic compounds to initiate plant defense responses. This study provided an overview of AMF-induced metabolites and metabolic pathways in plants under drought, focusing on the terpenoid profile.
Highlights
Crops are often subjected to abiotic stresses in the process of the growth and development, while abiotic stress activates relevant functional genes and metabolic pathways to mitigate the stress damage of crops (Giordano et al, 2021)
An important function of arbuscular mycorrhizal symbiosis is to accelerate the growth of the host plant, both under normal and unfavorable environmental conditions (Malhi et al, 2021)
Our study confirmed that R. intraradices strongly promoted shoot and root biomass production in trifoliate orange regardless of soil moisture content, and the promoting effect was relatively higher under drought conditions than under well-watered conditions
Summary
Crops are often subjected to abiotic stresses in the process of the growth and development, while abiotic stress activates relevant functional genes and metabolic pathways to mitigate the stress damage of crops (Giordano et al, 2021). Very few studies have attempted to use metabolomics tool to analyze metabolite changes caused by AMF inoculation under abiotic stress (e.g., drought and salinity) conditions (Rivero et al, 2018; Bernardo et al, 2019; Yang et al, 2020). Funneliformis mosseae mainly triggered sugars, lipids, and oleuropein lactones involved in stress mechanisms under drought stress (Bernardo et al, 2019). These limited studies still revealed that arbuscular mycorrhizal symbionts responded to stress by regulating metabolic plasticity (Rivero et al, 2018)
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