Mycorrhiza l tomato plants fine tunes the growth‐defencebalance upon N depleted root environments

Abstract

In low nutritive environments, the uptake of N by arbuscular mycorrhizal (AM) fungi may confercompetitive advantages for the host. The present study aims to understand how mycorrhizaltomato plants perceive and then prepare for an N depletion in the root environment. Plantscolonized by Rhizophagus irregularis displayed improved responses to a lack of N thannonmycorrhizal (NM) plants. These responses were accomplished by a complex metabolic andtranscriptional rearrangement that mostly affected the gibberellic acid and jasmonic acid path-ways involving DELLA and JAZ1 genes, which were responsive to changes in the C/N imbalanceof the plant. N starved mycorrhizal plants showed lower C/N equilibrium in the shoots thanstarved NM plants and concomitantly a downregulation of the JAZ1 repressor and the increasedexpression of the DELLA gene, which translated into a more active oxylipin pathway in mycorrhi-zal plants. In addition, the results support a priorization in AM plants of stress responses overgrowth. Therefore, these plants were better prepared for an expected stress. Furthermore, mostmetabolites that were severely reduced in NM plants following the N depletion remained unal-tered in starved AM plants compared with those normally fertilized, suggesting that the symbiosisbuffered the stress, improving plant development in a stressed environment.