** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** COTTON (GOSSYPIUM SPP.) IS A MAJOR CASH CROP AND THE LARGEST SOURCE OF NATURAL FIBER IN THE WORLD. THE MOST IMPORTANT CULTIVATED ALLOTETRAPLOID COTTON SPECIES ARE GOSSYPIUM HIRSUTUM (UPLAND COTTON) AND GOSSYPIUM BARBADENSE (PIMA COTTON), AMONG WHICH UPLAND CONTRIBUTES 90% OF THE WORLD&ACUTE;S COTTON FIBER PRODUCTION. ALTHOUGH CULTIVATED ONLY IN FEW REGIONS OF THE WORLD, G. BARBADENSE IS HIGHLY REGARDED FOR ITS SUPERIOR FIBER LENGTH, STRENGTH, AND FINENESS. ALTHOUGH COTTON IS A DROUGHT-TOLERANT PLANT, IT IS ALSO NEGATIVELY IMPACTED BY WATER-DEFICIT. WATER AND HEAT STRESS AFFECT SEVERAL GROWTH AND PHYSIOLOGICAL PROCESSES IN COTTON, ULTIMATELY AFFECTING COTTON FIBER YIELD AND QUALITY.THE COTTON FIBER IS A MULTILAYERED STRUCTURE THAT HAS BEEN STUDIED FOR MANY DECADES. IT CONSISTS OF A FIBRILLAR STRUCTURE COMPOSED OF A CUTICLE, A PRIMARY WALL, A SECONDARY WALL, AND A LUMEN. AT HIGH MAGNIFICATION, A COTTON FIBER LOOKS LIKE A TWISTED RIBBON OR A COLLAPSED AND TWISTED TUBE. THERE IS AN AVERAGE OF 60 OF THESE TWISTS OR CONVOLUTIONS PER CENTIMETER OF FIBER LENGTH. THE CONVOLUTIONS GIVE COTTON AN UNEVEN FIBER SURFACE THAT INCREASES INTER-FIBER FRICTION ENABLING THE FORMATION OF FINE COTTON YARNS OF ADEQUATE STRENGTH TO BE SPUN. THE PROPERTIES THAT DEFINE FIBER QUALITY ARE THE BASIS FOR MARKETING AND SALE OF COTTON WORLDWIDE. FIBER QUALITY IS DEFINED BROADLY BY LINEAR DENSITY, LENGTH, AND TENSILE PROPERTIES INFLUENCING YARN AND TEXTILE MANUFACTURING. THE GLOBAL COMPETITION IN THE PRODUCTION AND CONSUMPTION OF COTTON FIBER COMBINED WITH TECHNOLOGICAL PROGRESS IN YARN MANUFACTURING HAS TRIGGERED WORLDWIDE EFFORTS TO ENHANCE COTTON FIBER QUALITY. AS FIBER YIELD AND QUALITY ARE THE TWO MOST IMPORTANT TRAITS FOR COTTON PRODUCTION, SIGNIFICANT EFFORTS HAVE BEEN MADE TO UNDERSTAND THE BIOLOGICAL BASIS AND THE MOLECULAR MECHANISMS CONTROLLING COTTON FIBER DEVELOPMENT. A DETAILED KNOWLEDGE OF HOW THESE PROCESSES ARE REGULATED AT THE MOLECULAR AND CELLULAR LEVELS, AND HOW ENVIRONMENTAL CONDITIONS INFLUENCE THESE DETERMINANTS ARE FUNDAMENTAL TO DEVELOP NEW AND MORE EFFECTIVE STRATEGIES FOR COTTON FIBER PRODUCTION. FIBER DEVELOPMENT MUST BE REGULATED BY A GENETIC CIRCUIT THAT CONTROLS THE EXPRESSION OF GENES INVOLVED IN FIBER PRODUCTION AND ITS QUALITY CHARACTERISTICS. THEREFORE, IDENTIFYING THE GENES AND OR ALLELES THAT PLAY CENTRAL ROLES IN THE GENETIC CIRCUIT DETERMINING FIBER LENGTH AND QUALITY SHOULD PROVIDE INVALUABLE INFORMATION TO DESIGN BREEDING PROGRAMS FOR COTTON FIBER IMPROVEMENT.HOW CAN WE IDENTIFY GENES THAT PLAY IMPORTANT ROLES IN FIBER YIELD AND QUALITY? IT IS KNOWN THAT PIMA COTTON PRODUCES LONGER AND HIGHER QUALITY FIBERS THAN UPLAND COTTON BUT ALSO THAT HEAT AND DROUGHT STRESS REDUCE COTTON FIBER LENGTH AND QUALITY. THIS PROJECT AIMS AT DEVELOPING A DETAILED STUDY OF THE MOLECULAR BASIS OF THE DIFFERENCES BETWEEN PIMA AND UPLAND FIBER COTTON FORMATION AT THE CELL LEVEL, AND HOW ENVIRONMENTAL STRESSES AFFECT FIBER PRODUCTION. WE WILL TAKE ADVANTAGE OF,SINGLE-CELL TRANSCRIPTOMICS AND BIOINFORMATIC TOOLS TO IDENTIFY GENES PLAYING A KEY ROLE IN DETERMINING FIBER LENGTH AND QUALITY, AND GENES THAT ORCHESTRATE THESE COMPLEX PROCESSES. THE RESULTS OF THIS PROJECT WILL SIGNIFICANTLY CONTRIBUTE TO DEVELOPING BREEDING PROGRAMS WITH THE POTENTIAL TO PRODUCE COTTON VARIETIES WITH FIBER PROPERTIES THAT CAN BE ADAPTED TO THE FASTER AND MORE EFFICIENT SPINNING PLATFORMS CURRENTLY USED FOR SYNTHETIC FIBERS.