Significance Maize was domesticated from teosinte in Southern Mexico roughly 9,000 years ago. Maize originally was sensitive to photoperiod and required short-day conditions to flower. Thus, the reduced sensitivity to photoperiod is prerequisite for maize spread to long-day temperate regions. A gene encoding a CCT domain-containing protein, ZmCCT , was found by many researchers to modulate photoperiod sensitivity. The current study shows that insertion of a CACTA-like transposon into the ZmCCT promoter can suppress the ZmCCT expression remarkably and thus attenuates maize sensitivity under long-day conditions. The transposable element (TE) insertion event occurred in a tropical maize plant and has been selected for and accumulated as maize adapted to vast long-day environments. This selection leaves behind a TE-related linkage disequilibrium block with the very-low-nucleotide variations.