ZmTB1^be1 Modulates Ear Branching via Releasing the Repression to ZmWOX3a in Maize

The natural mutation of ZmTB1^WT to ZmTB1^be1 was documented as the fundamental cause of ear branching in maize, while the molecular mechanism remains undiscovered. In the present study, we characterized both ZmTB1^WT and ZmTB1^be1, and found that the structure of conserved domains, activation features, and subcellular localization of both proteins remained unchanged, whereas the mutation significantly decreased the transactivating power of ZmTB1^WT to the documented downstream target genes. Further DAP-qPCR identified significant enrichment of ZmTB1^be1 within the promoter of ZmWOX3a (pZmWOX3a), and the results of EMSA and Y1H indicated that ZmTB1^be1 could directly bind to pZmWOX3a. D-LUC assays showed that ZmTB1^WT significantly suppressed the activity of pZmWOX3a, while this suppression effect was completely released by the mutation of ZmTB1^be1. Furthermore, ZmTB1^WT exhibited statistically higher expression levels than ZmWOX3a within the tissues of immature ear and axillary buds at V7 under WT background, while ZmWOX3a possessed significantly stronger expression signals than ZmTB1^be1 under be1 background and ZmTB1^CR under ZmTB1^WT-edited backgrounds. The summary results of the present study hypothesize a novel cascade of ZmTB1^be1-ZmWOX3a in regulating ear branching, shedding a new light in understanding the female inflorescence development in maize.