Münster, August 26, 2026: The “Maryland Mammoth” tobacco variety was first described as early as 1906: While it flowers under short-day conditions, it grows to an extraordinary height under long-day conditions and produces no flowers at all. This unique trait made the variety an important model for research into photoperiodism—that is, the regulation of flowering by day length. However, the molecular cause remained unclear for more than a century.

Researchers at Fraunhofer IME and the University of Münster have now deciphered the genetic mechanism behind this historic phenotype. In the gene for the long-day flowering activator NtFT5, they found a deletion of two base pairs near the C-terminus. This results in a truncated protein, NtFT5^MM.

Small mutation, big impact

The altered protein can still interact with the transcription factor FD. However, its ability to trigger flowering is significantly reduced. Under long-day conditions, the downstream flowering genes are therefore not sufficiently activated. The plants remain in vegetative growth longer and thus reach their characteristic, extraordinary height.

The researchers provided functional evidence by overexpressing the intact NtFT5 gene from the day-neutral tobacco variety Hicks: “Maryland Mammoth” once again flowered reliably even under long-day conditions.

Further investigations show that the truncation does not impair either the transport or the stability of the protein. However, AlphaFold modeling suggests that the mutation weakens the binding of the flowering-activating protein complex to its target DNA. This establishes a direct mechanistic link between the molecular change and the plants’ distinctive growth behavior.

Implications for Plant Research and Breeding

The study links an agricultural phenotype that is more than a century old to a clearly defined molecular cause. It demonstrates that even a small mutation in a Florigen protein can significantly influence the timing of flowering, plant architecture, and adaptation to varying day lengths.

Paper
Grundmann L, Zimmermann MM, Iordanidis C, Känel A, Schwarze A, Wiedmann DR, Muth J, Twyman RM, Prüfer D, Noll GA 
A mutant allele of the long-day floral activator NtFT5 is associated with the short-day-specific flowering of tobacco cultivar Maryland Mammoth. Commun Biol 9, 1144 (2026). Link