ZmTB1be1 Modulates Ear Branching via Releasing the Repression to ZmWOX3a in Maize

Abstract

The natural mutation of ZmTB1WT to ZmTB1be1 was documented as the fundamental cause of ear branching in maize, while the molecular mechanism remains undiscovered. In the present study, we characterized both ZmTB1WT and ZmTB1be1, 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 ZmTB1WT to the documented downstream target genes. Further DAP-qPCR identified significant enrichment of ZmTB1be1 within the promoter of ZmWOX3a (pZmWOX3a), and the results of EMSA and Y1H indicated that ZmTB1be1 could directly bind to pZmWOX3a. D-LUC assays showed that ZmTB1WT significantly suppressed the activity of pZmWOX3a, while this suppression effect was completely released by the mutation of ZmTB1be1. Furthermore, ZmTB1WT 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 ZmTB1be1 under be1 background and ZmTB1CR under ZmTB1WT-edited backgrounds. The summary results of the present study hypothesize a novel cascade of ZmTB1be1-ZmWOX3a in regulating ear branching, shedding a new light in understanding the female inflorescence development in maize.