MADS-box genes play a pivotal role in various processes, including floral and seed development, controlling flowering time, regulation of fruits ripening, and respond to abiotic and biotic stressors in planta. Tobacco (Nicotiana tabacum) has been widely used as a model plant for analyzing the gene function, however, there has been less information on the regulation of flowering, and the associated genes. In the present study, a total of 168 NtMADS-box genes were identified from tobacco, and their phylogenetic relationship, chromosome locations, and gene structures were further analyzed. NtMADS-box genes can be clustered into four sub-families of Mα, Mγ, MIKC*, and MIKC^C. A total of 111 NtMADS-box genes were distributed on 20 chromosomes, and 57 NtMADS-box genes were located on the unanchored scaffolds due to the complex and incomplete assembly of the tobacco genome. Expression profiles of NtMADS-box genes by microarray from 23 different tissues indicated that members in different NtMADS-box gene subfamilies might play specific roles in the growth and flower development, and the transcript levels of 24 NtMADS-box genes were confirmed by quantitative real-time PCR. Importantly, overexpressed NtSOC1/NtMADS133 could promote early flowering and dwarfism in transgenic tobacco plants. Therefore, our findings provide insights on the characterization of NtMADS-box genes to further study their functions in plant development.

In tobacco, the basic helix-loop-helix (bHLH) transcription factor MYC2 contributes significantly to the biosynthesis and transport of nicotine, and also participates in the regulation of pollen development. However, their biological functions in seed germination remain largely unknown. Here, we examined the regulatory roles of NtMYC2a and NtMYC2b in abscisic acid (ABA) mediated seed germination. The expression of both NtMYC2a and NtMYC2b was repressed by ABA at both mRNA and protein levels. Simultaneous knock out of NtMYC2a and NtMYC2b reduced ABA signaling to promote seed germination, while overexpression of NtMYC2a or NtMYC2b resulted in the germinated seeds being more ABA-sensitive. Gene expression analysis showed that the expression of both NtABI3 and NtABI5 was reduced in Ntmyc2a/2b double mutants, but enhanced in transgenic plants overexpressing NtMYC2a or NtMYC2b. Both electrophoretic mobility shift assays (EMSA) and transient dual-luciferase reporter assays, revealed that both NtMYC2a and NtMYC2b could bind to the promoter of NtABI5 to activate its expression. Furthermore, NtMYC2a and NtMYC2b could interact with each other to form a heterodimer and function synergistically to activate the expression of NtABI5. Thus, these results provide evidence that the NtMYC2-NtABI5 module may function as a novel component in ABA signaling to positively modulate ABA-mediated seed germination in tobacco.