Mycorrhizal Fungi Enhance Resistance to Herbivores in Tomato Plants with Reduced Jasmonic Acid Production

Ludovico Formenti,Sergio Rasmann

doi:10.3390/agronomy9030131

Abstract

Arbuscular mycorrhizal (AM) fungi favor plant growth by improving nutrient acquisition, but also by increasing their resistance against abiotic and biotic stressors, including herbivory. Mechanisms of AM fungal mediated increased resistance include a direct effect of AM fungi on plant vigor, but also a manipulation of the hormonal cascades, such as the systemic activation of jasmonic acid (JA) dependent defenses. However, how AM fungal inoculation and variation in the endogenous JA production interact to produce increased resistance against insect herbivores remains to be further elucidated. To address this question, three genotypes of Solanum lycopersicum L., a JA-biosynthesis deficient mutant, a JA over-accumulating mutant, and their wild-type were either inoculated with AM fungi or left un-inoculated. Plant growth-related traits and resistance against Spodoptera littoralis (Boisduval) caterpillars, a major crop pest, were measured. Overall, we found that deficiency in JA production reduced plant development and were the least resistant against S. littoralis. Moreover, AM fungi increased plant resistance against S. littoralis, but such beneficial effect was more pronounced in JA-deficient plant than on JA over-accumulating plants. These results highlight that AM fungi-driven increased plant resistance is negatively affected by the ability of plants to produce JA and that AM fungi complement JA-mediated endogenous plant defenses in this system.

Highlights

Plants are the primary source of energy on Earth and are constantly under attack by higher trophic-level organisms such as herbivores and pathogens [1]
We found that deficiency in jasmonic acid (JA) production reduced plant development and were the least resistant against
We addressed the interactive effects of JA production and Arbuscular mycorrhizal (AM) fungi on plant growth and resistance against herbivores

Summary

Introduction

Plants are the primary source of energy on Earth and are constantly under attack by higher trophic-level organisms such as herbivores and pathogens [1]. The coordination of the plant defense responses to biotic attack is mediated by plant hormones [5], of which jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) are the most crucial. Other phytohormones, such as abscissic acid (ABA), gibberellins, auxins, and cytokinins, are emerging as important defense regulators as well [6,7]. Plants’ responses to leaf chewing herbivores are mainly mediated by JA and a related compound [8,9], which when activated, modify plants’ physical and chemical phenotypes, in general resulting in increased resistance against the attacker. Upon damage, a plant may enter in a state of priming for more rapid and intense response to a subsequent stress [10]

Methods

Results

Conclusion