Vernalization reveals distinct roles of FLOWERING LOCUS T homologs in floral transition of perennial Taraxacum koksaghyz

Flowering is a key trait in most crops and may depend on cold exposure, a process known as vernalization, but the underlying regulatory mechanisms are poorly understood. Taraxacum koksaghyz is a rubber-producing dandelion of the family Asteraceae, which also includes other economically important crops such as chicory and lettuce. Most T. koksaghyz plants require cold exposure to induce flowering, whereas vernalization-independent plants are more suitable for breeding. To elucidate the molecular mechanisms underlying vernalization dependency, we identified three FLOWERING LOCUS T (FT) homologs (TkFT1-3) with distinct expression patterns in response to environmental cues. At ambient temperatures, TkFT1 and TkFT2 are expressed in leaves under long-day conditions, whereas only TkFT1 is weakly expressed under short-day conditions. During cold exposure, TkFT1 expression in the leaves is abolished, but intriguingly, TkFT3 expression is induced exclusively during cold - a phenomenon not previously reported in herbaceous plants. Overexpression experiments revealed that TkFT1-3 bypass the vernalization requirement in T. koksaghyz and promote early flowering in vernalization-independent T. brevicorniculatum, probably by inducing the FRUITFULL homologs TkFUL1 and TkFUL2, which we identified as downstream targets. Our findings highlight a previously unrecognized role of an FT homolog in cold-induced flowering and suggest that TkFT1 promotes vernalization-independent flowering, whereas TkFT3 expression during cold exposure is required for vernalization-dependent flowering. This study demonstrates the function and regulation of FT genes controlling flowering time in T. koksaghyz, contributing to a broader understanding of vernalization-dependent flowering and providing knowledge that can be used in the future to facilitate breeding.