Abstract
Plant association with arbuscular mycorrhizal fungi (AMF) can increase their ability to overcome multiple stresses, but their impact on plant interactions with herbivorous insects is controversial. Here we show higher mortality of the leaf-chewer Spodoptera exigua when fed on tomato plants colonized by the AMF Funneliformis mosseae, evidencing mycorrhiza-induced resistance. In search of the underlying mechanisms, an untargeted metabolomic analysis through ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS) was performed. The results showed that mycorrhizal symbiosis had a very limited impact on the leaf metabolome in the absence of stress, but significantly modulated the response to herbivory in the damaged area. A cluster of over accumulated metabolites was identified in those leaflets damaged by S. exigua feeding in mycorrhizal plants, while unwounded distal leaflets responded similar to those from non-mycorrhizal plants. These primed-compounds were mostly related to alkaloids, fatty acid derivatives and phenylpropanoid-polyamine conjugates. The deleterious effect on larval survival of some of these compounds, including the alkaloid physostigmine, the fatty acid derivatives 4-oxododecanedioic acid and azelaic acid, was confirmed. Thus, our results evidence the impact of AMF on metabolic reprograming upon herbivory that leads to a primed accumulation of defensive compounds.
Highlights
Plants are highly dynamic systems that are able to react to, 2020; Pozo et al, 2020)
In order to determine whether root colonization by F. mosseae affects S. exigua performance, tomato plants displaying a well-established mycorrhizal symbiosis were challenged with S. exigua larvae
Larvae fed on F. mosseae-colonized tomato plants (Fm) showed a higher mortality than those feeding in nonmycorrhizal plants (Nm; Fig. 2)
Summary
Plants are highly dynamic systems that are able to react to, 2020; Pozo et al, 2020). The association of plants with AMF and other beneficial microbes can stimulate the plant’s immune system, rendering the plant more resistant to the attack by different aggressors. This ‘alert’ state is known as induced systemic resistance (ISR; Choudhary et al, 2007; Pieterse et al, 2014). Priming is a low-cost defensive strategy since plant defences are not (or only slightly) activated in the absence of stress, but they are strongly triggered in response to a challenge (Mauch-Mani et al, 2017)
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