**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** POTATO IS THE THIRD HIGHEST CONSUMED STAPLE CROP IN THE WORLD. ONE OF THE SIGNIFICANT THREATS TO POTATO CROP PRODUCTION IS MICROORGANISMS THAT CAUSE PLANT DISEASES. SUCH ORGANISMS ARE GENERALLY NAMED PLANT PATHOGENS. THERE ARE AROUND 75 POTATO PATHOGENS THAT HAVE BEEN RECOGNIZED IN THE US. THE PROPOSED RESEARCH FOCUSES ON TWO POTATO PATHOGENS, SPONGOSPORA SUBTERRANEA F. SP. SUBTERRANEA (SSS) AND POTATO MOP-TOP VIRUS (PMTV). THESE PATHOGENS CAUSE POWDERY SCAB AND POTATO MOP-TOP DISEASES, RESPECTIVELY. SSS CAUSES SCABBY LESIONS ON POTATO TUBER SKIN AND GALLING ON POTATO ROOTS. SEVERE ROOT GALL FORMATION CAN REDUCE THE PLANT UPTAKE OF NUTRIENTS AND WATER LEADING TO STUNTED GROWTH. SSS ALSO TRANSMITS PMTV, FACILITATING ITS SURVIVAL IN THE SOIL AND ENTRY INTO THE PLANT. THE SURVIVAL SPORES (CYSTOSORI) PRODUCED BY SSS CAN SURVIVE IN THE SOIL FOR OVER TEN YEARS AND CARRY PMTV. PMTV INFECTION CAN ALSO DAMAGE THE POTATO TUBER, CAUSING NECROSIS IN THE TUBER FLESH. THE TUBER DAMAGE CAUSED BY SSS AND PMTV MAKES THE TUBER UNSUITABLE FOR FRESH MARKET AND PROCESSING. UNFORTUNATELY, THERE ARE NO SUCCESSFUL CHEMICAL CONTROL METHODS AVAILABLE FOR SSS OR PMTV. THEREFORE, DISEASE MANAGEMENT IS MAINLY PREVENTATIVE VIA PATHOGEN-FREE SEED TUBERS AND NON-CONTAMINATED FIELDS. ALTERNATIVELY, POTATO CULTIVARS WITH PARTIAL AND SPORADIC RESISTANCE COULD BE USED TO MINIMIZE DISEASE IMPACT. WHILE THE MECHANISM OF POTATO DISEASE RESISTANCE TO SSS AND PMTV IS UNKNOWN, VARYING RESISTANCE AMONG DIFFERENT POTATO CULTIVARS HAS BEEN OBSERVED. HOWEVER, THE LACK OF COMPLETE RESISTANCE IN COMMERCIALLY FAVORABLE CULTIVARS CAN MAKE SUPPRESSING POWDERY SCAB AND MOP-TOP DISEASES USING RESISTANT CULTIVARS CHALLENGING.IN EVERY LIVING ORGANISM, INCLUDING PLANTS, GENES DETERMINE THE INHERENT TRAITS. WHILE SOME GENES IN AN ORGANISM ARE EXPRESSED AT ALL TIMES, OTHER GENES ARE EXPRESSED AS RESPONSES TO EXTERNAL STIMULI. PLANT PATHOGEN INFECTION IS ONE SUCH STIMULUS THAT AFFECTS GENE EXPRESSION IN PLANTS. SOME GENES EXPRESSED AFTER A PATHOGEN INFECTION ARE DIRECTLY ASSOCIATED WITH RESISTANCE OR SUSCEPTIBILITY OF THE PLANT TO THE RESPECTIVE PATHOGEN. BOTH PRIOR STUDIES AND OUR DATA HAVE SHOWN THAT THE DIFFERENT POTATO CULTIVARS WITH DIFFERENT SSS RESISTANCES SHOW DIFFERING EXPRESSION OF GENES WHEN CHALLENGED WITH SSS.THUS, THE MAIN GOAL OF THE PROPOSED PROJECT IS TO IDENTIFY AND CHARACTERIZE THE FUNCTION OF GENES INVOLVED IN THE INTERACTION AMONG POTATO, SSS, AND PMTV. WE HYPOTHESIZE THAT BY IDENTIFYING THE DIFFERENTIALLY EXPRESSED GENES IN CULTIVARS WITH DIFFERENT RESISTANCES, WE CAN IDENTIFY POTATO GENES THAT ORIGINATE RESISTANCE AGAINST SSS AND PMTV. ALSO, COMPARING GENE EXPRESSIONS IN SSS BEFORE AND DURING INTERACTION CAN REVEAL THE GENES INVOLVED IN THE INTERACTION BETWEEN SSS AND PMTV.TO ACHIEVE THIS GOAL, WE PROPOSE THE FOLLOWING METHODS. FIRST, THREE SELECTED POTATO CULTIVARS WITH VARYING RESISTANCE TO SSS/PMTV WILL BE INOCULATED WITH SSS WITH AND WITHOUT PMTV. NEXT, THE GENE EXPRESSION OF E,ACH SAMPLE WILL BE READ USING ESTABLISHED SEQUENCING TECHNOLOGIES. THEN, USING MULTIPLE BIOINFORMATICS TOOLS, THE GENE EXPRESSION OF EACH CULTIVAR UNDER EACH INFECTION CONDITION WITH COMPARED WITH ONE ANOTHER TO IDENTIFY GENES THAT ARE UNIQUE TO EACH HOST-PATHOGEN INTERACTION. FINALLY, WE WOULD CONFIRM THE EFFECT OF CANDIDATE GENES IDENTIFIED THROUGH THE ABOVE PROCESS USING GENETIC ENGINEERING METHODS. ALL WORK WILL BE DONE IN LABORATORY AND GREENHOUSE SETTINGS, AND GENETICALLY MODIFIED MATERIALS WILL NOT BE RELEASED INTO THE EXTERNAL ENVIRONMENT.THE RESISTANCE AND PATHOGENICITY GENES DISCOVERED FROM THIS STUDY CAN BE USED DIRECTLY TO CONTROL SSS AND PMTV IN MULTIPLE WAYS. PHENOTYPE-BASED SCREENING FOR RESISTANCE IN CONVENTIONAL BREEDING PROGRAMS COULD BE TIME-CONSUMING AND MISLEADING, AS DISEASE SYMPTOM EXPRESSION DEPENDS HEAVILY ON POTATO CULTIVARS AND THE ENVIRONMENT. THIS PROJECT WILL BOOST THE EFFICIENCY OF BREEDING PROGRAMS BY IDENTIFYING GENES THAT CAN BE USED AS SELECTION MARKERS FOR RESISTANCE CULTIVAR SCREENING. ALSO, RESISTANCE GENES IDENTIFIED IN THE PROPOSED WORK CAN BE USED AS A TARGET FOR GENETIC MODIFICATION IN BREEDING PROGRAMS IN THE FUTURE, ACCORDING TO PROPER STATE AND FEDERAL REGULATIONS AND GUIDELINES. INFORMATION GATHERED ON PATHOGEN VIRULENCE GENES COULD CONTRIBUTE TO DISEASE CONTROL VIA HOST GENOME MODIFICATION-BASED PATHOGEN CONTROL METHODS. OVERALL, THE PROPOSED WORK WILL LEAD TO THE DEVELOPMENT OF PLANT RESISTANCE AGAINST POWDERY SCAB AND POTATO MOP-TOP DISEASES, REDUCING ECONOMIC LOSSES AND CONTRIBUTING TO FOOD SECURITY. BOOSTING PLANT RESISTANCE WILL REDUCE THE USE OF PARTIALLY EFFECTIVE FUNGICIDES, EASING DETRIMENTAL EFFECTS ON THE ENVIRONMENT AND HUMAN HEALTH.GENETIC MECHANISMS OF PLANT VIRUS TRANSMISSION BY PROTISTS REMAIN LARGELY UNKNOWN. THE PROPOSED STUDY WILL GENERATE NOVEL KNOWLEDGE ON THE GENOMIC BASIS OF SUCH TRIPARTITE INTERACTIONS AND CONTRIBUTE TO BUILDING A PATHOGENESIS MODEL OF PLANT-PROTIST INTERACTIONS. SUCH A MODEL CAN HELP UNDERSTAND AND CONTROL SIMILAR HOST-PROTIST INTERACTIONS. THEREFORE, THE PROPOSED WORK SIGNIFICANTLY ADVANCES THE SCIENTIFIC UNDERSTANDING OF PLANT HOST-PATHOGEN INTERACTIONS.