Abstract
Besides improved mineral nutrition, plants colonised by arbuscular mycorrhizal (AM) fungi often display increased biomass and higher tolerance to biotic and abiotic stresses. Notwithstanding the global importance of wheat as an agricultural crop, its response to AM symbiosis has been poorly investigated. We focused on the role of an AM fungus on mineral nutrition of wheat, and on its potential protective effect against Xanthomonas translucens. To address these issues, phenotypical, molecular and metabolomic approaches were combined. Morphological observations highlighted that AM wheat plants displayed an increased biomass and grain yield, as well as a reduction in lesion area following pathogen infection. To elucidate the molecular mechanisms underlying the mycorrhizal phenotype, we investigated changes of transcripts and proteins in roots and leaves during the double (wheat-AM fungus) and tripartite (wheat-AM fungus-pathogen) interaction. Transcriptomic and proteomic profiling identified the main pathways involved in enhancing plant biomass, mineral nutrition and in promoting the bio-protective effect against the leaf pathogen. Mineral and amino acid contents in roots, leaves and seeds, and protein oxidation profiles in leaves, supported the omics data, providing new insight into the mechanisms exerted by AM symbiosis to confer stronger productivity and enhanced resistance to X. translucens in wheat.
Highlights
Many studies have focused on local and systemic transcriptomic and proteomic changes in rice[8,9,10], maize[11], Medicago truncatula12,13) and tomato plants[14,15,16]
We observed in RM a significant increase in phenylalanine (Phe) and threonine, as expected by the down-regulation of lactoylglutathione lyase, which is involved in threonine degradation
We found W5ALA0, a protein highly homologous to ERDJ3B in Arabidopsis, involved in regulating protein folding in the endoplasmic reticulum lumen and which is necessary for pathogen-associated molecular pattern (PAMP)-triggered immunity[70]; W5B9I7, a protein showing 80% identity with NAA10 in Arabidopsis, and which is involved in plant immunity by maintaining homeostasis of the immune receptors SNC1 and RPM171; and the Cell Division Cycle 5-like protein (CDC5) that, in addition to its function during mitosis, is a core component of protein complexes that positively regulate defence responses through splicing and small RNA processing[72]
Summary
Many studies have focused on local and systemic transcriptomic and proteomic changes in rice[8,9,10], maize[11], Medicago truncatula12,13) and tomato plants[14,15,16]. The mechanisms involved in the bio-protective effect of AM fungi are not fully explained: they are not exclusively dependent on the improved mineral nutrition, but seem to be related to activation of plant defence mechanisms[26]. Establishment of an AM symbiosis and production of AM signals activate defence-responsive genes in both shoot and root[12,27,28,29] This boost of basal defences is known as priming, and it could be successfully triggered by various natural and artificial compounds, including AM fungi[30]. We looked for the main pathways involved in enhancing plant biomass and mineral nutrition, and in promoting the bio-protective effect against a leaf pathogen. To address these issues, we combined phenotypic, and molecular metabolomic approaches. Mineral and amino acid contents in roots, leaves and seeds, and protein oxidation profiles in leaves, supported the omics data, providing new insight into the mechanisms exerted by AM symbiosis to confer positive effects on wheat development, and resistance to a wheat pathogen
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