About this Research Topic
In 1999, two back-to-back papers appeared in The Plant Cell, reporting the cloning of FLOWERING LOCUS C (FLC) in the model plant Arabidopsis thaliana. The FLC locus encodes a MADS box transcription factor that blocks the transition to flowering until after winter. Vernalization, a prolonged period of exposure to cold, is a requirement for several temperate plant species (with natural variation therein) in order to promote flowering in spring time. Discovery of FLC in Arabidopsis opened the door for understanding how vernalization is controlled at the molecular level. Vernalization down-regulates FLC expression, rendering Arabidopsis competent to flower. FLC acts by directly repressing expression of key flowering-promoting genes, including FLOWERING LOCUS T (FT). Photoperiod lengthening in spring time triggers flowering via the long day floral promotion pathway. In the Brassicaceae, how FLC expression is regulated to control flowering, and reset during meiosis, has received considerable attention, owing to the numerous modes of gene regulation that act in concert on the one locus. Recent evidence in Arabidopsis suggests plants can separate different thermosensory inputs (including high temperature spikes and prolonged cold) across different time scales (hourly through to seasonal) to promote vernalization.
Progress has also been made in various legumes, cereals, beets, onions, and perennials, on how vernalization acts to promote flowering and bud dormancy break, primarily via activation of FT genes. In cereals, vernalization regulates the floral activator and repressor, VERNALIZATION 1 and 2 (VRN1, 2) respectively, to activate FT. VRN2 in cereals acts in an ‘FLC-like’ manner to repress flowering. In the annual legume, Medicago truncatula, certain loci have been characterized that are responsive to vernalization and act genetically upstream of FT genes. In response to seasonal cues, including vernalization, FT family members act antagonistically to control different aspects of plant development in onion and beets. What has become clear is that preventing ectopic expression of FT is important. However, in plants that have evolved a vernalization requirement, the immediate targets of vernalization and the molecular mechanisms to promote spring flowering, still remain to be unraveled for several species.
In light of recognizing the 20th anniversary of the landmark papers first identifying FLC as the principal target of vernalization to promote flowering in Arabidopsis, this Research Topic seeks submissions of various types (including original research, reviews, hypotheses, and perspectives) studying aspects of the vernalization pathway across various plant families. With the onset of climate change, and the imminent need to increase the food supply (and the quality thereof), advances in the underlying mechanisms behind the vernalization pathway in plants are paramount, for inclusion in plant breeding strategies for the future.
Keywords: Vernalization, Flowering time, FLC, FT
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