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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.

Approximately 29% of all vascular plant species are unable to establish an arbuscular mycorrhizal (AM) symbiosis. Despite this, AM fungi (Rhizophagus spp.) are enriched in the root microbiome of the nonhost Arabidopsis thaliana, and Arabidopsis roots become colonized when AM networks nurtured by host plants are available. Here, we investigated the nonhost–AM fungus interaction by analyzing transcriptional changes in Rhizophagus, Arabidopsis and the host plant Medicago truncatula while growing in the same mycorrhizal network. In early interaction stages, Rhizophagus activated the Arabidopsis strigolactone biosynthesis genes CCD7 and CCD8, suggesting that detection of AM fungi is not completely impaired. However, in colonized Arabidopsis roots, fungal nutrient transporter genes GintPT, GintAMT2, GintMST2 and GintMST4, essential for AM symbiosis, were not activated. RNA-seq transcriptome analysis pointed to activation of costly defenses in colonized Arabidopsis roots. Moreover, Rhizophagus colonization caused a 50% reduction in shoot biomass, but also led to enhanced systemic immunity against Botrytis cinerea. This suggests that early signaling between AM fungi and Arabidopsis is not completely impaired and that incompatibility appears at later interaction stages. Moreover, Rhizophagus-mediated defenses coincide with reduced Arabidopsis growth, but also with systemic disease resistance, highlighting the multifunctional role of AM fungi in host and nonhost interactions., This work was supported by the grant Marie Skłodowska-Curie Individual Fellowship ‘AraMyco’ H2020-MSCA-IF-2014 (to IF), grant no. 823.02.019 of the Netherlands Organization of Scientific Research (NWO), VIDI grant no. 11281 of the Dutch Technology Foundation STW (to SCMVW), and ERC Advanced Investigator grant no. 269072 of the European Research Council (to CMJP).

Defense priming conditions diverse\ud plant species for the superinduction\ud of defense, often resulting in\ud enhanced pest and disease resistance\ud and abiotic stress tolerance.\ud Here, we propose a guideline that\ud might assist the plant research\ud community in a consistent assessment\ud of defense priming in plants.

Evolution has provided plants with sophisticated defensive strategies to "perceive" attack by pathogens and insects, and to translate that "perception" into an appropriate adaptive response. Plant innate immunity is based on a surprisingly complex response that is highly flexible in its capacity to recognize and respond to the invader encountered. In the past years, we explored Arabidopsis as a model to study the molecular basis of rhizobacteria-induced systemic resistance (ISR). We discovered novel components of the ISR signaling pathway and revealed that priming for augmented expression of pathogenresponsive genes plays an important role in this type of induced resistance. Currently our research is also focused on the question: how are plants capable of integrating microbial- and insect-induced signals into defense responses that are specifically directed against the attacker? The alarm signals salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) are major regulators of plant defense. Their signaling pathways cross-communicate, providing the plant with a regulatory potential to fine-tune its defense reaction. We discovered that the regulatory protein NPR1 functions as a modulator in cross-talk between SA and JA, thereby helping the plant to "decide" which defensive strategy to follow, depending on the type of attacker encountered, and that this function of NPR1 is conserved among Arabidopsis accessions all over the world, suggesting an importany role for plant survival.

Durante o processo evolucionário, as plantas adquiriram uma sofisticada estratégia defensiva para ´perceber´ os ataques de patógenos e insetos, traduzindo essa percepção em uma resposta apropriada e de forma adaptativa. A imunidade inata da planta é baseada surpreendemente na resposta complexa que é altamente flexível nas suas capacidades de reconhecer e responder aos mais diversos invasores. Já faz muito tempo que a planta Arabidopsis tem sido utilizada como modelo para estudos moleculares de resistência sistêmica induzida por rizobactérias (RSI). Atualmente, nossa pesquisa é focada em uma questão: Como as plantas são capazes de integrar sinais induzidos por insetos e microorganismos em respostas específicas contra esses invasores? Os sinais de alarmes de ataque, ácido salicílico, jasmônico e etileno são os principais reguladores da defesa das plantas. As rotas de sinalização se intercalam, fornecendo as plantas um grande potencial de regulação para uma defesa refinada. Recentemente, nós descobrimos que a proteína NPR1 funciona com um modulador da comunicação entre as rotas de sinalização do ácido salicílico e do ácido jasmônico, e desse modo, ajuda a planta a ´decidir´ qual estratégia de defesa tomar, dependendo do tipo de invasor encontrado. Aqui, nós apresentamos uma revisão de nossa pesquisa nos últimos anos.

Plants in their environment face potential deleterious organisms such as fungi, bacteria, viruses, nematodes, etc. Many of them are able to cause plant diseases, responsible of important losses in crop production worldwide. But often the outcome of these interactions is not disease, since plants have developed multiple mechanisms to protect themselves against pathogens attack. Moreover, beneficial microorganisms are common in the soil, improving plant growth and reducing the effects of deleterious organisms. While chemical control of plant diseases is usually expensive and may have a negative impact on the environment and on public health, the use of microorganisms to control plant pathogens, known as biological control, is accepted as a durable and environmentally friendly alternative in plant disease management.