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WRINKLED1 (WRI1), an <i>APETALA2</i> (AP2) transcription factor (TF), critically regulates the processes related to fatty acid synthesis, storage oil accumulation, and seed development in plants. However, the <i>WRI1</i> genes remain unknown in allohexaploid bread wheat (<i>Triticum aestivum</i> L.). In this study, based on the sequence of Arabidopsis <i>AtWRI1</i>, two <i>TaWRI1Ls</i> genes of bread wheat, <i>TaWRI1L1</i> and <i>TaWRI1L2</i>, were cloned. <i>TaWRI1L2</i> was closely related to monocotyledons and clustered in one subgroup with <i>AtWRI1</i>, while <i>TaWRI1L1</i> was clustered in another subgroup with <i>AtWRI3</i> and <i>AtWRI4</i>. Both were expressed highly in the developmental grain, subcellular localized in the nucleus, and showed transcriptional activation activity. <i>TaWRI1L2</i>, rather than <i>TaWRI1L1</i>, promoted oil body accumulation and significantly increased triglyceride (TAG) content in tobacco leaves. Overexpression of <i>TaWRI1L2</i> compensated for the functional loss of <i>AtWRI1</i> in an Arabidopsis mutant and restored the wild-type phenotypes of seed shape, generation, and fatty acid synthesis and accumulation. Knockout of <i>TaWRI1L2</i> reduced grain size, 1000 grain weight, and grain fatty acid synthesis in bread wheat. Conclusively, <i>TaWRI1L2</i>, rather than <i>TaWRI1L1</i>, was the key transcriptional factor in the regulation of grain fatty acid synthesis in bread wheat. This study lays a foundation for gene regulation and genetic manipulation of fatty acid synthesis in wheat genetic breeding programs.