Mycorrhiza-induced resistance as a hub for plant immunity against pathogens and pests

• Autores: Dulcenombre de María Manresa Grao
• Directores de la Tesis: Víctor Flors (dir. tes.), Mª Victoria Pastor Fuentes (dir. tes.)
• Lectura: En la Universitat Jaume I ( España ) en 2024
• Idioma: inglés
• Número de páginas: 222
• Tribunal Calificador de la Tesis: M. Jose Pozo Jiménez (presid.), Antoni Garcia Molina (secret.), Rosa Sánchez Lucas (voc.)
• Programa de doctorado: Programa de Doctorado en Ciencias por la Universidad Jaume I de Castellón
• Materias:
  • Ciencias agrarias
• Enlaces
  • Tesis en acceso abierto en: TDX
• Resumen

  • Plants are in continuous contact with their environment. The interaction with biotic and abiotic elements makes the plant to adjust continuously its metabolism. Some of these interactions can be deleterious for the plant, thus to cope with these stressors, like pathogen and insect herbivores, plants have developed a sophisticated immune system that can recognize the attacker and activate specific immune responses. In addition, the plant immune system could be activated upon appropriate stimuli. This process is known as Induced Resistance (IR) and is activated through either a xenobiotic and a biotic or abiotic agent. When the stimulus used is an Arbuscular Mycorrhizal Fungi, the interaction is known as Mycorrhiza Induced Resistance (MIR). MIR confers resistance against a wide range of pathogens and pests through Jasmonic Acid (JA)-dependent responses. Our group has demonstrated previously that MIR activates faster defensive responses when the plant is infected by Botrytis cinerea. However, the main mechanisms responsible for the perception of this necrotrophic fungus are still unclear. On the other hand, most studies about plant-herbivore interactions are focused on chewing insects while the effectiveness of MIR against spider mites has received a less attention.

    Due the abovementioned issues, the general aim of this PhD thesis is to achieve an advanced characterization of the mechanisms of MIR that confers resistance in two different pathosystems in which immune responses are regulated by the JA-signalling pathway: (a) tomato plants against the necrotroph B. cinerea and (b) two citrus genotypes with different levels of basal resistance against the polyphagous spider mite Tetranychus urticae.

    Regarding the former, our results show that a priming of the peptide hormone systemin perception and early signalling kinase cascade mediate MIR response in tomato against B. Cinerea. Using Virus-gene silencing (VIGs) we have demonstrated that SYR1/2, PORK1, involved in systemin perception, and the early signalling kinase cascade (MPK3, MPK2 and MPK1) are key elements of MIR through pathogen perception. Moreover, a multi-omic study of mychorrizal tomato plants upon the same pathogen demonstrates that symbiosis produces a huge molecular reprograming in the plant, initiating the transcriptional and translational machinery of the plant preparing it to have a specific response upon a following attack. Regarding the spider mite-citrus interactions, a faster activation of JA-dependent responses (LOX2, PR3, OPDA, JA-Ile) was observed in both mycorrhizal genotypes at locally infested tissue confirming that JA is a key regulator of citrus defense against spider mites. In addition, through a metabolomic studies, pharmacological assays and chemical inhibition of the phenylpropanoids pathway, we determined that the biosynthesis of flavonoids is a key factor in the defense of mycorrhizal citrus plants against the mite. Furthermore, we propose that Abscisic Acid (ABA) is an important player in the resistance of mycorrhizal citrus plants (C. reshni) against this pest. Finally, despite antibiosis was reinforced by MIR in both genotypes, we only observed an enhancement of antixenosis, systemic and indirect defense against T. urticae in the susceptible genotype. Hence, we have demonstrated that MIR is genotype-dependent and inversely correlated to the basal resistance of the citrus against the insect.

    Finally, thanks to the aforementioned results, it has been shown that MIR is a multi-faceted process which offers a tailored response against different biotic stresses, giving rise to a wide range of possible agronomical applications for this plant beneficial microorganism.