** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** APHIDS ARE LIKE THE VAMPIRES OF THE PLANT, USING A SPECIALIZED PIERCING-SUCKING MOUTHPART TO FEED ON THE PHLOEM FOR LONG PERIODS OF TIME (8+ HOURS). DURING THIS PROCESS, THE PLANT AND APHID ARE EACH MOUNTING DEFENSES AGAINST THE OTHER, WITH THE PLANT TRYING TO STOP THE APHID FROM FEEDING AND THE APHID TRYING TO STOP THE PLANT FROM DEFENDING ITSELF. FROM THE PLANT SIDE, IT WILL PRODUCE REACTIVE OXYGEN SPECIES (ROS) AND CALCIUM (CA2+) THAT SEND SIGNALS TO THE REST OF THE PLANT TO DEFEND ITSELF, AS WELL AS STOP THE FLOW OF PHLOEM TO THE APHID. THE APHID IN TURN IS SPITTING INTO THE PLANT A COMPLEX MIXTURE OF SALIVA THAT CAN STOP THESE DEFENSES, EITHER BY REDUCING THE ROS OR BINDING UP THE CA2+, AMONGST OTHER STRATEGIES. CURRENTLY, WHAT IS KNOWN ABOUT APHID SALIVA IS THAT IS CONTAINS A DIVERSE MIXTURE OF PROTEINS, EACH WITH A UNIQUE FUNCTION TO AID THE APHID IN FEEDING. HOWEVER, RECENTLY I HAVE DISCOVERED ANOTHER COMPONENT OF THE SALIVA THAT MAY HAVE AN IMPORTANT ROLE IN APHID MANIPULATION OF THE PLANT CALLED SMALL MOLECULES. SMALL MOLECULES, INCLUDING COMPOUNDS KNOWN AS METABOLITES, CAN INTERACT WITH PLANT PROTEINS OR DEFENSE COMPOUNDS TO MANIPULATE PLANT PHYSIOLOGY. ONE OF THE MOST ABUNDANT METABOLITES I FOUND IN APHID SALIVA WAS CITRIC ACID (CA) AND MALIC ACID (MA). THESE TWO METABOLITES ARE ESSENTIAL COMPONENTS OF METABOLISM IN MANY ORGANISMS, INCLUDING THE PLANT. THEY SERVE TO PRODUCE ENERGY FOR THE PLANT, AS WELL AS PRECURSORS OF OTHER IMPORTANT COMPOUNDS IN THE PLANT LIKE AMINO ACIDS AND ANTIOXIDANTS, MOLECULES THAT SCAVENGE ROS. I ALSO FOUND A DIVERSITY OF DIPEPTIDES (DPS) IN APHID SALIVA, AN EMERGING CLASS OF COMPOUNDS THAT CAN SERVE AS ANTIOXIDANTS AND/OR REGULATE CELLULAR METABOLISM. INTRIGUINGLY, NONE OF THE DPS I HAVE DISCOVERED IN APHID SALIVA HAVE A KNOWN FUNCTION. OVERALL, MY PRELIMINARY FINDINGS SUGGEST THAT APHID SALIVARY METABOLITES ARE A PROMISING NEW AVENUE OF RESEARCH IN PLANT-APHID INTERACTIONS FOR THEIR POTENTIAL TO MITIGATE THE PLANT DEFENSE RESPONSE. THIS RESEARCH AREA IS IMPORTANT AS IT HAS RELEVANCE TO BASIC RESEARCH, INVESTIGATING HOW PLANT PHYSIOLOGY IS REGULATED BY APHID SALIVA, AS WELL AS APPLIED RESEARCH IN DISCOVERING NEW NOVEL COMPOUNDS, SUCH AS DPS, THAT ARE INVOVLED PLANT ADAPTATION OR SUSCEPTIBILITYTO APHIDS.IN ORDER TO INVESTIGATE THE ROLE OF APHID SALIVARY METABOLITES IN THE PLANT-APHID INTERACTION, I WILL EMPLOY A VARIETY OF TECHNIQUES TO CHARACTERIZE FIRST (1) HOW APHID FITNESS IS IMPACTED ON PLANTS WITH INCREASED CA, MA, AND DPS IN THE PLANT AND (2) HOW THE PLANT FITNESS CHANGES IN RESPONSE TO THESE COMPOUNDS. FOR OBJECTIVE 1, I WILL USE APHID BIOASSAYS THAT MEASURE THE GROWTH AND SURVIVAL OF APHIDS ON PLANTS WITH INCREASED CA, MA, AND/OR DPS. I WILL ALSO USE A POWERFUL TOOL CALLED ELECTRICAL PENETRATION GRAPH (EGP) TO MEASURE APHID FEEDING, WHICH INDICATES APHID SUCCESS ON THE HOST PLANT. FOR OBJECTIVE 2, I WILL INVESTIGATE HOW THE CA, MA, AND DPS ARE IMPACTING PLANT PHYSIOLOGY AND DEFENSE RESPONSES TO APHI,DS. CA AND MA ARE BOTH CENTRAL CARBON METABOLITES, WHICH CAN BE INCORPORATED INTO PLANT METABOLISM. USING STABLE-ISOTOPE CARBON, I CAN TRACE APHID-SALIVARY METABOLITES IN THE METABOLIC FLUX OF THE PLANT AND IDENTIFY WHICH COMPOUNDS, SPECIFICALLY ANTIOXIDANTS, ARE MADE IN THE PLANT FROM APHID SALIVA. ADDITIONALLY, CA, MA, AND DPS ARE FOUND TO DAMPEN THE ROS AND CA2+ RESPONSE OF THE PLANTS, AND THEREBY PLANT DEFENSES. TO INVESTIGATE THIS POTENTIAL ROLE OF SALIVARY METABOLITES, I WILL USE FLUORESCENT REPORTER LINES OF ARABIDOPSIS TO VISUALIZE ROS AND CA2+ SIGNALING INTENSITY AND DURATION IN PLANTS WITH AND WITHOUT INCREASED CA, MA, AND DPS AFTER APHID INFESTATION. IF THESE METABOLITES ARE FOUND TO DECREASE THE ROS AND CA2+ RESPONSE, I WILL FURTHER VALIDATE THEIR FUNCTION IN A RECIPROCAL APPROACH USING ROS AND CA2+ SIGNALING MUTANTS. TOGETHER, THESE RESULTS WILL BEGIN TO UNCOVER THE ROLE OF SALIVARY METABOLITES IN THE PLANT-APHID INTERACTION AND PROVIDE METHODOLOGY FOR STUDYING THE SALIVARY METABOLITES OF OTHER APHID SPECIES IN AGRONOMICALLY IMPORTANT CROPS.