A previously overlooked genetic network may help explain why tobacco plants rapidly produce side shoots after their main growing tip is removed. New research has identified 118 MADS-box genes across the tobacco genome and linked several of them to axillary bud development, the process that determines whether dormant buds at the junction between leaves and stems remain suppressed or grow into branches. The study, published in Plant Cell Reports, highlights one gene in particular, NtMADS91, which preliminary experiments suggest can stimulate the growth of these buds, increasing both their number and their length. The finding could provide a new molecular target for controlling tobacco plant architecture, yield, and the labor-intensive management of axillary shoots.
Axillary buds are among the most strategically controlled structures in a plant. They form in leaf axils, where leaves meet the stem, and can remain dormant while the main shoot dominates growth. When the shoot tip is removed, a practice known as topping, the balance of hormones and mobile signals changes almost immediately. In tobacco, topping is widely used to redirect resources toward leaves, but it also releases axillary buds from apical control. These buds may then develop into unwanted shoots, competing for nutrients and altering leaf quality. Although hormones such as auxin, cytokinin, abscisic acid, and strigolactone are known to influence this process, the transcription factors that translate these signals into developmental decisions have remained insufficiently understood in tobacco.
The new study focuses on MADS-box proteins, a large family of DNA-binding transcription factors that act as molecular regulators of plant development. These proteins typically recognize specific DNA sequences in gene promoters and recruit other regulatory proteins, allowing them to switch developmental programs on or off. MADS-box factors are best known for their roles in floral organ identity, flowering time, fruit development, and meristem maintenance, but evidence from other species has increasingly connected them with branching, bud dormancy, and plant architecture. Their influence comes partly from their ability to form protein complexes, meaning that a single MADS-box protein may produce different effects depending on which partners are present in a particular tissue.
By searching the tobacco genome, the researchers catalogued 118 genes carrying MADS-box domains. Phylogenetic analysis divided them into two broad evolutionary groups: type I genes, including the Mα and Mγ subfamilies, and type II genes, including the MIKC* and MIKCᶜ clades. The distinction is important because the two groups differ in their evolutionary history, protein structure, and biological specialization. Type II MADS-box proteins generally contain the characteristic MIKC architecture, with regions involved in DNA binding, protein interaction, and transcriptional regulation. The tobacco gene family is comparatively large, reflecting the complex evolutionary history of the tobacco genome and its hybrid origin, while also raising the possibility that duplicated genes have acquired specialized roles in different tissues.
The researchers next examined the regulatory landscapes surrounding these genes. Promoter analysis revealed numerous cis-acting elements associated with light responses and plant hormones. Such elements are short DNA sequences that can be recognized by upstream regulatory proteins, enabling environmental or physiological signals to influence gene activity. Their abundance does not prove that a gene directly responds to a particular hormone, but it provides a molecular explanation for why MADS-box genes might participate in the dynamic response of axillary buds after topping. Light availability, auxin distribution, cytokinin activity, abscisic acid accumulation, and strigolactone signaling can all alter bud behavior, and the promoter architecture suggests that MADS-box genes may function where these pathways converge.
To identify genes associated with bud activation, the team analyzed RNA sequencing data from tobacco axillary buds collected after topping. The comparison revealed 60 NtMADS-box genes whose expression changed significantly. From this group, 12 candidates showing particularly notable expression shifts were selected for additional investigation. Quantitative reverse-transcription PCR, a technique that measures messenger RNA abundance, was then used to examine their activity in different tissues. Seven genes displayed preferential expression in axillary buds, indicating that their activity was not simply a general consequence of wounding or shoot removal. Members of the SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1, or SOC1, and SHORT VEGETATIVE PHASE, or SVP, subfamilies represented a substantial proportion of these bud-associated candidates.
SOC1 and SVP are traditionally associated with flowering and seasonal development, making their apparent involvement in axillary bud growth especially intriguing. In model plants, SOC1 integrates signals from several flowering pathways, while SVP helps regulate developmental transitions and can interact with other MADS-box proteins. The tobacco results suggest that related factors may be redeployed in axillary buds, where they could help coordinate developmental timing with hormonal status. This does not mean that flowering and branching are controlled by identical mechanisms. Rather, plants may reuse versatile transcriptional regulators in different tissues, connecting the decision to grow a branch with broader programs governing meristem identity, cell division, and developmental phase.
Hormone treatments provided another clue. Applying abscisic acid, commonly abbreviated ABA, and GR24, a synthetic analog used to mimic strigolactone activity, significantly reduced the expression of most candidate genes, including NtMADS91. ABA is widely associated with the maintenance of bud dormancy and stress-responsive growth restraint, while strigolactones are major suppressors of shoot branching. The response of NtMADS91 and related genes to both compounds places them downstream of, or closely connected to, hormonal pathways that normally restrict axillary bud development. However, expression changes alone cannot establish the exact direction of the regulatory relationship. The genes might be direct targets of hormone-responsive factors, or their activity could be altered indirectly through changes in bud metabolism and growth.
The most provocative result came from preliminary overexpression experiments involving NtMADS91. Tobacco plants engineered to produce higher levels of this gene developed axillary buds that were more numerous and longer than those of control plants. This pattern is consistent with the possibility that NtMADS91 promotes bud initiation or outgrowth, potentially counteracting the suppressive effects of ABA and strigolactone signaling. Yet the authors describe the evidence as preliminary, and several questions remain unanswered. It is not yet clear whether the gene acts directly on cell-cycle regulators, hormone metabolism, meristem identity genes, or transport processes that determine nutrient and signal flow into the bud. It is also unknown whether the observed phenotype depends on developmental stage, plant genotype, environmental conditions, or the precise level and location of gene expression.
The discovery arrives as researchers seek more precise ways to manage plant architecture without relying exclusively on manual removal, chemical treatments, or broad changes in cultivation practices. In tobacco production, axillary shoots can influence leaf biomass, quality, and the distribution of plant resources, making their control an important agronomic objective. A deeper understanding of NtMADS-box genes could eventually support breeding strategies that produce varieties with predictable branching behavior or enable targeted genetic interventions. Such applications remain distant: candidate genes must first be validated through loss-of-function experiments, complementation tests, protein-interaction studies, and direct identification of their DNA targets. The researchers’ dataset, including the RNA-sequencing results deposited in ScienceDB, provides a foundation for those investigations. For now, NtMADS91 stands as a compelling lead in a broader genetic network that may reveal how tobacco plants convert hormonal signals into the visible architecture of their shoots.
Subject of Research: MADS-box transcription factors and axillary bud development in tobacco
Article Title: Genome-wide characterization of MADS-box genes and their roles in axillary bud development in tobacco
Article References: Ren, Y., Wang, R., Deng, M. et al. “Genome-wide characterization of MADS-box genes and their roles in axillary bud development in tobacco.” Plant Cell Reports 45, 266 (2026).
Image Credits: AI Generated
DOI: https://doi.org/10.1007/s00299-026-03946-y
Keywords: MADS-box transcription factor, axillary bud development, tobacco, Nicotiana tabacum, NtMADS91, abscisic acid, strigolactone, GR24, SOC1, SVP, shoot branching
Tags: axillary bud development in tobaccogene regulation of side shoot growthgenetic mechanisms of axillary shoot emergenceMADS-box gene family in plantsmolecular targets for crop yield improvementNtMADS91 gene functionplant architecture controlplant developmental biologyplant hormone signaling in bud dormancytobacco cultivation practicesTobacco plant geneticstobacco plant management strategies
