Duplication and functional divergence of TCP4 genes in turnip

Gene duplication is widely recognized as a significant catalyst for plant adaptive evolution. The retained duplicated genes usually undergo functional divergence to govern plant growth and stress resistance. Turnip (Brassica rapa var. rapa) shows a broad capacity for environmental adaptation. Here, we investigate how duplicated TCP4 genes modulate turnip growth and development. We identify three TCP4 paralogs, BrrTCP4, BrrTCP4a and BrrTCP4b in turnip, characterize their expression patterns and analyze sequence variation in their conserved domains. We further model their three-dimensional structures and compare their protein-protein interactions and downstream regulatory networks. We show that BrrTCP4, BrrTCP4a and BrrTCP4b exhibit distinct expression profiles. A single mutation within the conserved TCP domain leads to differences in protein-protein interactions among BrrTCP4, BrrTCP4a and BrrTCP4b. Combined with DAP-Seq, ChIP-qPCR and luciferase assays, our results demonstrate that BrrTCP4 and BrrTCP4a activate BrrCOs and BrrFTs to regulate turnip flowering, while BrrTCP4b preferentially participates in the trehalose synthesis pathway by targeting TPP and TPS genes. Our research findings indicate the functional divergence of BrrTCP4, BrrTCP4a and BrrTCP4b to balance growth and stress responses in turnip, thereby advancing our understanding of how gene duplication drives functional specialization and contributes to plant evolutionary adaptation.