THE BASELINE OF THE PROJECT IS THE STUDY OF THE MYCORRHIZA-INDUCED RESISTANCE (MIR) AGAINST PATHOGENS AND ARTHROPODS. DIFFERENT AND PROMISING RESULTS FROM PREVIOUS PROJECTS, PROMPTED US TO GO IN DEPTH IN SEVERAL MECHANISMS OF MIR, AS WELL AS TO EXPLORE NEW ASPECTS OF THE PEST MANAGEMENT USING MYCORRHIZAL FUNGI. ONE OF THE FOCUS OF OUR PREVIOUS PROJECT WAS TO TEST WHETHER MIR IS LINKED TO THE PEPTIDE SYSTEMIN (SYS). RECENT PUBLICATIONS HAVE DESCRIBED THE ELUSIVE RECEPTOR OF THE PEPTIDE (SYR1 AND SYR2) AND THE POSTTRANSLATIONAL CLEAVAGE OF THE PROTOPEPTIDE PROSYSTEMIN TO RELEASE THE ACTIVE FORM OF THE PEPTIDE SYS (BY TWO PHYTASPASES AND A LEUCINE AMINOPEPTIDASE). WITH THESE NOVEL MOLECULAR/MECHANISTIC TOOLS WE AIM TO STUDY THE REGULATORY ROLE OF SYS IN DEFENSE PRIMING DURING MIR BY MONITORING THE PROCESSING OF THE PROSYSTEMIN, SYS PERCEPTION AND THE SIGNAL TRANSDUCTION DURING MIR, UPON BOTRYTIS CINEREA INFECTION. WE WILL FOCUS ON WHETHER MIR CAN PRIME OR STIMULATE THIS PROCESS CONTRIBUTING TO A MORE EFFICIENT RESPONSE AGAINST THE PATHOGEN. INTERESTINGLY, ALONG THE STUDIES OF THE PREVIOUS AGL PROJECT (RESYSTEMIC), WE FOUND THAT MIR SHARES WITH SYS-INDUCED RESISTANCE SEVERAL METABOLIC RESPONSES AND BOTH SEEM TO BE MEDIATED BY CALLOSE ACCUMULATION. THEREFORE, WE PROPOSE TO DECIPHER THE PRIMING-CALLOSE PATHWAY IN MIR BY STUDYING THE CONTRIBUTION OF SUGAR MOBILIZATION AND THE INTERPLAY BETWEEN CALLOSE, REACTIVE OXYGEN SPECIES (ROS) AND ABA. IN OTHER PLANT SPECIES WE DEMONSTRATED THAT CALLOSE ACCUMULATION IN RESPONSE TO PAMPS IS PRECEDED BY A PEAK OF ROS THAT REQUIRES INTACT ABA SIGNALING, BOTH CALLOSE ACCUMULATION AND ROS ARE ENHANCED IN PRIMING. REGARDING CALLOSE ACCUMULATION IN MIR THERE IS STILL A GAP IN THE KNOWLEDGE ABOUT THE LINK BETWEEN SUGAR AVAILABILITY, AND SUGARS TRANSPORT FROM THE CYTOPLASM TO THE CELL WALL. TAKING ALL TOGETHER, WE WILL ANALYZE WHETHER THE MIR OR SYS PERCEPTION MAY ALTER THE ROS STATUS IN PLANTS MYCORRHIZED AND TREATED, RESPECTIVELY. WE ALSO AIM TO FOLLOW THE EVENTS AFTER (OR SIMULTANEOUSLY) TO ROS IMBALANCE. BECAUSE THE OXIDATION PROCESS PRECEDES THE REINFORCEMENT OF CELL WALL, WE EXPECT STARCH MOBILIZATION BY MEANS OF A BETA AMYLASE ACTIVATION. BETA AMYLASES ARE RESPONSIBLE TO CONVERT STARCH INTO SUGARS, THUS WE WILL INVESTIGATE WHETHER THE SUGARS RELEASED AFTER STARCH DEGRADATION ARE TRANSPORTED THROUGH THE VESICULAR TRAFFICKING, WHICH INVOLVES THE ABC TRANSPORTER SYP121, CONTRIBUTING TO THE PRIMING OF CALLOSE DURING MIR. DUE TO THE GOOD RESULTS OBTAINED IN MIR AGAINST B. CINEREA, IT IS PROPOSED ALSO AN EXPLORATORY SEARCH TO GAIN KNOWLEDGE IN THE PEST MANAGEMENT USING MYCORRHIZA AS A MEAN OF SUSTAINABILITY. IN THIS REGARD WE ATTEMPT TO STUDY THE EFFECTIVENESS OF MIR IN TWO DIFFERENT CROPS OF HIGH ECONOMICAL INTEREST IN OUR AREA: TOMATO AND CITRUS. FOR SUCH PURPOSE, A TRIPARTITE APPROACH WILL BE USED BY USING NATURAL PREDATORS OF THE TWO SPOTTED SPIDER MITE TETRANYCHUS URTICAE. TO THIS END, TAKEN INTO ACCOUNT THE LINE OF COLLABORATION BETWEEN DR. FLORS AND DR. JAQUES (THE LAST ONE, RECENTLY INCORPORATED TO THE CONSORTIUM), WE WILL EXPLORE THE INTERPLAY BETWEEN HERBIVORE-INDUCED RESISTANCE AND MIR THROUGH THE USE OF TWO ZOOPHYTOPHAGOUS MITES THAT LIKELY TRIGGER DEFENSE RESPONSES IN THE AM PLANTS WHAT MAY ALTER THE DEFENSIVE STATUS OF THE PLANT.