A B3 Domain Transcription Factor NtMAB1 Regulates the Release and Outgrowth of Axillary Buds in Tobacco

The release and outgrowth of axillary buds are essential parts of the process of shoot branching in plants, but knowledge of the underlying regulatory mechanisms remains limited. Analysis of mab1-D, a tobacco mutant with a greater number of axillary branches, showed that the mutant phenotype resulted from positive modulation of axillary buds release and outgrowth. TAIL-PCR and co-separation analyses suggested that NtMAB1-S1, a member of the Related to ABI3/VP1 (RAV) subfamily that was highly expressed in the base of axillary buds, was associated with the mutant phenotype. Phenotypic analyses of mab1-D overexpression, knockdown, knockout and complementation lines demonstrated that NtMAB1-S1 was a positive regulator of axillary buds release and outgrowth. NtMAB1-S1 accelerated these processes through transcriptional repression via the B3 repression domain. RNA-sequencing analysis revealed that NtMAB1-S1 was involved in the trehalose-6-phosphate and gibberellin metabolism pathways. Moreover, NtMAB1-S1 enhanced the release and outgrowth of axillary buds by directly repressing transcription of NtTPPF, a trehalose-6-phosphate phosphatase, and NtGA2ox8, a gibberellin oxidase. NtMAB1-S1 thus plays a pivotal role in regulating the release and outgrowth of axillary buds and is a potential target for genetic interventions aimed at shaping ideal plant architecture.