Early events of the innate immunity activation by the fungal elicitor AsES in strawberry

GUSTAVO GABRIEL MARTOS; MARÍA DEL MILAGRO TERÁN; JUAN CARLOS DIAZ RICCI

Congreso; IPMB - 11th International Congress of Plant Molecular Biology; 2015

Throughout the evolution of plants they have developed an elaborate system of control of their metabolism that allows them to respond and adapt to their environment. This control system comprises a complex signaling network that is unparalleled in other living organisms and involves the participation of specialized receptors, hormones and a variety of metabolites that act in an integrated manner in cells reprogramming cells the gene expression and activating metabolic pathways strategically in response to various stimuli that the plant receives. In a plant / pathogen interaction, plant cells are capable of recognizing certain molecules produced by inducing pathogens and activating a cascade of reactions leading to a defense response. Previous studies conducted in our laboratory let identify a new inducing plant defense called AsES, which is produced by the fungus Acremonium strictum, and is capable of inducing a strong defense response that protects strawberry plants against the virulent pathogen Collecotrichum acutatum, responsible for anthracnose. Later, it was also proved the activity of AsES on Arabidopsis thaliana plants, which gave them a resistance against the necrotrophic pathogen Botrytis cinerea. It is known that each inductor of the defense may have a particular and distinctive way to activate the immune response of plants. This work describes some of the most important cellular events associated with the activation of the immune response induced AsES. The results showed that aces does not require the integrity of the apoplast, or the interaction with a target soluble effector in the apoplast, to activate the defense response in strawberry plants. It was observed that AsES produces a rapid and transient depolarization of the plasmatic membrane and the leakage of ions, followed by a signal of Ca2 + which precedes and modulates the early accumulation of nitric oxide (NO). Besides, AsES causes the alkalinization of the extracellular space and induces a simultaneous increase of the extracellular H2O2 and a decrease of the intracellular H2O2, during the first post induction hour. Experiments with transformed tobacco Fld plants, indicated that possibly the intracellular H2O2 which initially decreases after induction with AsEs is of chloroplast origin. It was observed that AsES generates a three-phase oxidative burst in strawberry cells, with a first stage of gradual and sustained increase in the extracellular H2O2 during the first hour, followed by a biphasic intracellular accumulation with peaks at the 2 and 7 hours post treatment. It was also possible to observe the real-time production of nitric oxide in the chloroplasts of strawberry cells and cells of Vicia faba guard, yielding the maximum accumulation at 10 minutes after treatment with AsES. It was also shown that AsES acts similarly as ABA promoting the closure and the inhibition of the opening of Vicia faba stomata. Both events indicate that AsES active physiological mechanisms related to defense, depending of Ca2 +, ON and H2O2.