Metabolic transition in mycorrhizal tomato roots.

Javier Rivero,Ricardo Aroca,Jordi Gamir,María J Pozo,Víctor Flors

doi:10.3389/fmicb.2015.00598

Abstract

Beneficial plant–microorganism interactions are widespread in nature. Among them, the symbiosis between plant roots and arbuscular mycorrhizal fungi (AMF) is of major importance, commonly improving host nutrition and tolerance against environmental and biotic challenges. Metabolic changes were observed in a well-established symbiosis between tomato and two common AMF: Rhizophagus irregularis and Funneliformis mosseae. Principal component analysis of metabolites, determined by non-targeted liquid chromatography–mass spectrometry, showed a strong metabolic rearrangement in mycorrhizal roots. There was generally a negative impact of mycorrhizal symbiosis on amino acid content, mainly on those involved in the biosynthesis of phenylpropanoids. On the other hand, many intermediaries in amino acid and sugar metabolism and the oxylipin pathway were among the compounds accumulating more in mycorrhizal roots. The metabolic reprogramming also affected other pathways in the secondary metabolism, mainly phenyl alcohols (lignins and lignans) and vitamins. The results showed that source metabolites of these pathways decreased in mycorrhizal roots, whilst the products derived from α-linolenic and amino acids presented higher concentrations in AMF-colonized roots. Mycorrhization therefore increased the flux into those pathways. Venn-diagram analysis showed that there are many induced signals shared by both mycorrhizal interactions, pointing to general mycorrhiza-associated changes in the tomato metabolome. Moreover, fungus-specific fingerprints were also found, suggesting that specific molecular alterations may underlie the reported functional diversity of the symbiosis. Since most positively regulated pathways were related to stress response mechanisms, their potential contribution to improved host stress tolerance is discussed.

Highlights

Beneficial organisms are common in the rhizosphere and they provide important ecosystem services (Philippot et al, 2013)
This study aims to decipher the impact of a wellestablished mycorrhizal association with two widespread and well characterized arbuscular mycorrhizal fungi (AMF) (F. mosseae and R. irregularis) in the root metabolic profile of a non-legume, tomato (Solanum lycopersicum), where the benefits of arbuscular mycorrhizas (AM) have been shown to be agronomically relevant in terms of stress resistance and fruit quality (Pozo et al, 2002; Fritz et al, 2006; Aroca et al, 2008; Gianinazzi et al, 2010; Barzana et al, 2012; Giovannetti et al, 2012; Zouari et al, 2014)
Absence of fungal structures was confirmed in roots of the non-mycorrhizal controls, and the extent of root length colonized by F. mosseae or R. irregularis differed significantly (Figure 1C, p < 0.01)

Summary

Introduction

Beneficial organisms are common in the rhizosphere and they provide important ecosystem services (Philippot et al, 2013) They can greatly contribute to plant performance by improving nutrition, stress tolerance and plant phenotypic plasticity, an important advantage in heterogeneous environments where precise allocation of limited resources between growth and stress resistance is critical for survival (Pozo et al, 2015). Among these beneficial organisms, Metabolomics in mycorrhizal tomato roots soil-borne fungi from the phylum Glomeromycota, known as arbuscular mycorrhizal fungi (AMF) deserve special attention. A precise regulation of host hormone levels has been proposed as a central mechanism in the regulation of the interaction (Pozo et al, 2015)

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