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Summary: Grain length is one of the most important factors in determining wheat yield. Here, a stable QTL for grain length was mapped on chromosome 1B in a F10 recombinant inbred lines (RIL) population, and the gene TaGL1‐B1 encoding carotenoid isomerase was identified in a secondary large population through multiple strategies. The genome‐wide association study (GWAS) in 243 wheat accessions revealed that the marker for TaGL1‐B1 was the most significant among all chromosomes. EMS mutants of TaGL1 possessed significantly reduced grain length, whereas TaGL1‐B1‐overexpressed lines possessed significantly increased grain length. Moreover, TaGL1‐B1 strongly interacted with TaPAP6. TaPAP6‐overexpressed lines had significantly increased grain length. Transcriptome analysis suggested that TaPAP6 was possibly involved in the accumulation of JA (jasmonic acid). Consistently, JA content was significantly increased in the TaGL1‐B1 and TaPAP6 overexpression lines. Additionally, the role of TaGL1‐B1 in regulating carotenoids was verified through QTL mapping, GWAS, EMS mutants and overexpression lines. Notably, overexpression of TaGL1‐B1 significantly increased wheat yield in multiple locations. Taken together, overexpression of TaGL1‐B1 enhanced grain length, probably through interaction with TaPAP6 to cause the accumulation of JA that improved carotenoid content and photosynthesis, thereby resulted in increased wheat yield. This study provided valuable genes controlling grain length to improve yield and a potential insight into the molecular mechanism of modulating JA‐mediated grain size in wheat. [ABSTRACT FROM AUTHOR]