Metabolomic Analysis Of Durum Wheat Roots In Response to Arbuscular Mycorrhizal Fungi Inoculation in Field Conditions

Arbuscular mycorrhizal (AM) fungi are commonly occurring fungi that live in an obligate symbiotic status with the majority of land plants. The objective of the present work was to gain insight into the root metabolism changes (primary and secondary metabolism) of durum wheat in response to solely AM fungi inoculation or to combination of AM fungi with plant growth promoting rhizobacteria (PGPR) (Bacillus spp.). Field trial was performed in 2010–2011 in a typical semi-arid Mediterranean area (inner land of Sicily) in absence of fertilization. The untarget metabolomics analysis using the Agilent GC–quadrupole MS identified metabolites playing a key role in symbiosis as well as in root physiology during plant-microbe interactions in field conditions. Aminoacids was the category of compounds most affected by microrganism inoculation. Six of the 20 identified aminoacids significantly differed among the three treatments (natural, AM fungi, AM fungi + PGPR inoculation). They were tyrosine, tryptophan, threonine, ornithine, lysine, glutamine. In the AM fungi + PGPR treatment only tyrosine and lysine were lower than natural conditions. Oxoproline and glutamine were higher in AM fungi + PGPR treatment in comparison to solely AM fungi treatment. Six out of the 48 analysed carbohydrates (including pentitol, fructose, and cellobiose) significantly varied among the treatments as well as 7 out of the 22 analysed organic acids. Four among them were highly significantly altered: malic acid, isocitric acid, gluconic acid, arachidic acid. The treatment AM fungi + PGPR significantly downregulated only the aconitic acid. Inoculation with AM fungi as well as AM fungi + PGPR treatment severely modified the content of some key fatty acids and diterpene alcohols such as palmitoleic acid, isoheptadecanoic acid, ergosterol and phytol. Also myristic acid and monopalmitin significantly varied among treatment even though at a lower extent. Fifty one compounds belonging to the secondary metabolism were analysed: 41 were lipids and 11 were classified as other metabolites. Overall both AM fungi and AM fungi + PGPR treatments did not drastically alter lipid pathways since only four metabolites significantly varied. A principal component analysis highlighted which metabolites mostly contributed to the variability among the three treatments. The physiological consequences of metabolic changes induced by mycorrhyzal in both presence/absence of plant growth promoting bacteria were discussed