Genome-wide characterization of MADS-box genes and their roles in axillary bud development in tobacco

MADS-box transcription factors are core regulators of plant development, but their functions in axillary bud development in Nicotiana tabacum L. have not been systematically elucidated. In this study, 118 NtMADS-box genes were identified from the tobacco genome. Phylogenetic analysis classified them into Type I (comprising the Mα and Mγ subfamilies) and Type II (comprising the MIKC* and MIKCC clades). Promoter analysis revealed that cis-acting elements were predominantly associated with light and hormone responses. RNA-seq analysis of axillary buds after topping identified 60 differentially expressed NtMADS-box genes, from which 12 candidate genes with significant expression changes were selected. Tissue-specific qRT-PCR revealed that seven of these genes were preferentially expressed in axillary buds, among which members of the SOC1 and SVP subfamilies accounted for the majority. Exogenous application of abscisic acid and the strigolactone analog GR24 significantly suppressed the expression of most candidate genes, including NtMADS91. Functional analysis demonstrated that overexpression of NtMADS91 significantly promoted axillary bud growth, increasing both the number and length of axillary buds. This study provides a theoretical basis for elucidating the regulatory mechanism of the NtMADS-box gene family in axillary bud development and also offers important candidate genes for research related to tobacco axillary bud development.