Fraunhofer Institute for Molecular Biology and Applied Ecology IMEFrom wild to crop plant: precisely controlling the flowering-time
T. koksaghyz is a diploid, perennial wild plant in the Asteraceae family. It produces high-quality natural rubber, as well as other valuable compounds, such as inulin and triterpenes. Since it grows in temperate regions and thrives in nutrient-poor soils, it is an environmentally friendly alternative to the tropical rubber tree (Hevea brasiliensis). However, the pronounced vernalization dependence of many genotypes poses a significant obstacle to breeding: the plants often require prolonged exposure to cold to develop synchronous and vigorous flowering, which is a prerequisite for efficient seed production. Therefore, a deeper understanding of the exogenous and endogenous factors that control the transition from the vegetative to the generative phase is essential. The researchers aim to develop vernalization-independent plants with shorter life cycles to enable more reliable seed production. This could significantly contribute to meeting the world’s growing demand for natural rubber.
Three FT genes as key flowering activators in dandelion
The genetic networks that govern flowering induction in the annual model plant Arabidopsis thaliana have been extensively studied. However, other species sometimes deviate significantly from this model. The FT protein appears to be a key regulatory hub across many species, though. It integrates various external and internal factors, such as temperature, day length, and age, and thus controls the timing of flowering.
In T. koksaghyz, three hierarchically interacting genetic loci control the cold-dependent flowering induction, indicating the complex architecture of the underlying genetic network. To unravel these relationships, researchers at Fraunhofer IME and the University of Münster are collaborating closely. This joint effort combines basic molecular research and applied plant biotechnology to develop new genotypes and breeding approaches.
As part of joint research activities, three FT genes (TkFT1–3) were identified in dandelions. Their key role in controlling flowering time was confirmed. Vernalization and day length interact in a "photothermal" synergy that significantly influences flower formation. Increasing the activity of the TkFT genes causes plants that are normally cold-dependent to flower without exposure to cold. In the closely related, cold-independent species T. brevicorniculatum, overexpressing these genes leads to premature flowering. These results clearly demonstrate that the three TkFT proteins are potent flowering activators.
However, their distinct expression patterns are particularly revealing. Under warm conditions, TkFT1 and TkFT2 are primarily activated during long days, which is a classic signal for the initiation of flowering in temperate latitudes. In this context, TkFT1 reacts strongly to temperature. During the cold phase, its expression is completely suppressed, rising again afterward only in vernalization-independent genotypes. TkFT3, on the other hand, follows a different regulatory logic. This gene is activated exclusively during cold exposure and turns off once it ends. A strictly winter-active FT signal has not been previously described in herbaceous plants. This limited activation suggests that TkFT3 does not directly trigger flower formation but rather establishes flowering competence first. Flowering competence is the ability of the shoot meristem to transition into generative development after winter under suitable conditions.
Flowering control is particularly complex in perennial plants because they must alternate between vegetative growth and reproductive phases year after year. Unlike annual species, they cannot permanently dedicate all meristems to reproduction; they must maintain some vegetatively in order to grow and flower again in subsequent years. The functional differentiation of the three FT genes suggests that T. koksaghyz developed a regulatory strategy for this that differs from the Arabidopsis model. TkFT3 mediates the cold-specific flowering competence signal in vernalization-dependent genotypes, and TkFT1 induces flowering in vernalization-independent genotypes under suitable temperature and day length conditions.
Relevance for breeding and seed production
The results of this collaborative project provide valuable insights into possible mechanisms of cold-dependent control of flowering time in perennial plants. At the same time, the results offer concrete starting points for breeding. Specifically modulating the activity of individual FT genes could identify or generate genotypes that are less dependent on a cold phase in the future. These developments would accelerate seed production, shorten breeding cycles, and significantly advance the establishment of T. koksaghyz as a sustainable crop, which is an important step toward diversifying the global supply of natural rubber.
