**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** CROP PLANTS WITH TROPICAL OR SUBTROPICAL ORIGINS ARE SUSCEPTIBLE TO CHILLING STRESSES WHICH IS OCCURRING MORE FREQUENTLY WITH GLOBAL CLIMATE CHANGE. BREEDING CHILLING TOLERANT PLANTS IS LIMITED BY A LACK OF UNDERSTANDING OF TOLERANCE MECHANISMS AND A SCARITY OF GENES AND GENE VARIANTS THAT CAN BE USED IN BREEDING. IN ORDER TO IDENTIFY IMPORTANT GENES AND VARIANTS FOR CHILLING TOLERANCE, WE HAVE CONDUCTED GENOME WIDE ASSOCIATION STUDIES AND HAVE ISOLATED A RICE CASEIN KINASE GENE CTK1 AS A MAJOR FACTOR FOR NATURAL VARIATIONS OF CHILLING TOLERANCE IN RICE. WE HAVE FURTHER IDENTIFIED THE RIBOSOME PROTEIN RPS6 AS ITS POTENTIAL PHOSPHORYLATION TARGET UNDER CHILLING.THE GOAL OF THIS STUDY IS TO GAIN A FURTHER UNDERSTANDING OF CHILLING TOLERANCE MECHANISMS THROUGH THE STUDY OF CTK1 AND ITS NATURAL VARIANTS IN BOTH RICE AND MAIZE. WE WILL TEST TWO HYPOTHESES IN CHILLING TOLERANCE MECHANISMS. 1) CTK1 MODULATES CHILLING TOLERANCE THROUGH ITS PHOSPHORYLATION OF RPS6 AND ITS MODULATION OF RIBOSOME ACTIVITIES; 2) NATURAL VARIATIONS OF CTK1 CAN BE EXPLORED FOR IMPROVING CHILLING TOLERANCE IN RICE AND MAIZE. THIS WILL BE ACHIEVED THROUGH FIVE SPECIFIC OBJECTIVES. 1) THE EFFECTS OF CTK1 ON RPS6 UNDER CHILLING WILL BE EXAMINED. 2) THE DIRECT PHOSPHORYLATION OF RPS6 BY CTK1 WILL BE TESTED. 3) THE EFFECT OF CTK1 ON GLOBAL TRANSLATION ACTIVITY DURING CHILLING WILL BE EXAMINED. 4) THE EFFECT OF PHOSPHORYLATION STATUS OF RPS6 ON CHILLING TOLERANCE WILL BE INVESTIGATED. 5) ELITE CTK1 ALLELES FOR CHILLING TOLERANCE PROMOTION WILL BE IDENTIFIED.THIS RESEARCH WILL GENERATE NOVEL KNOWLEDGE ON CHILLING TOLERANCE MECHANISMS ESPECIALLY ON THE ROLE OF TRANSLATION MODULATION IN CHILLING RESPONSE. IT WILL ALSO PROVIDE GENES AND GENETIC VARIANTS FOR IMPROVING CHILLING TOLERANCE AND TO MITIGATE THE ADVERSE EFFECTS OF CLIMATE CHANGES ON CROP PRODUCTIVITY.