Vernalization

History of vernalization research

In the history of agriculture, farmers observed a traditional distinction between "winter cereals", whose seeds require chilling (to trigger their subsequent emergence and growth), and "spring cereals", whose seeds can be sown in spring, and germinate, and then flower soon thereafter. Scientists in the early 19th century had discussed how some plants needed cold temperatures to flower. In 1857 an American agriculturist John Hancock Klippart, Secretary of the Ohio Board of Agriculture, reported the importance and effect of winter temperature on the germination of wheat. One of the most significant works was by a German plant physiologist Gustav Gassner who made a detailed discussion in his 1918 paper. Gassner was the first to systematically differentiate the specific requirements of winter plants from those of summer plants, and also that early swollen germinating seeds of winter cereals are sensitive to cold.

In 1928, the Soviet agronomist Trofim Lysenko published his works on the effects of cold on cereal seeds, and coined the term "яровизация" (yarovizatsiya : "jarovization") to describe a chilling process he used to make the seeds of winter cereals behave like spring cereals (from яровой : yarvoy, Tatar root ярый : yaryiy meaning ardent, fiery, associated with the god of spring). Lysenko himself translated the term into "vernalization" (from the Latin vernum meaning Spring). After Lysenko the term was used to explain the ability of flowering in some plants after a period of chilling due to physiological changes and external factors. The formal definition was given in 1960 by a French botanist P. Chouard, as "the acquisition or acceleration of the ability to flower by a chilling treatment."

Lysenko's 1928 paper on vernalization and plant physiology drew wide attention due to its practical consequences for Russian agriculture. Severe cold and lack of winter snow had destroyed many early winter wheat seedlings. By treating wheat seeds with moisture as well as cold, Lysenko induced them to bear a crop when planted in spring. Later however, according to Richard Amasino, Lysenko inaccurately asserted that the vernalized state could be inherited, i.e. the offspring of a vernalized plant would behave as if they themselves had also been vernalized and would not require vernalization in order to flower quickly. Opposing this view and supporting Lysenko's claim, Xiuju Li and Yongsheng Liu have detailed experimental evidence from the USSR, Hungary, Bulgaria and China that shows the conversion between spring wheat and winter wheat, positing that "it is not unreasonable to postulate epigenetic mechanisms that could plausibly result in the conversion of spring to winter wheat or vice versa."

Early research on vernalization focused on plant physiology; the increasing availability of molecular biology has made it possible to unravel its underlying mechanisms. For example, a lengthening daylight period (longer days), as well as cold temperatures are required for winter wheat plants to go from the vegetative to the reproductive state; the three interacting genes are called VRN1, VRN2, and FT (VRN3).

In ''Arabidopsis thaliana''

Arabidopsis thaliana ("thale cress") is a much-studied model for vernalization. Some ecotypes (varieties), called "winter annuals", have delayed flowering without vernalization; others ("summer annuals") do not.{{cite web |url= http://www.plant-biology.com/vernalisation-response.php |access-date=2011-01-26

The reproductive phase change of A. thaliana occurs by a sequence of two related events: first, the bolting transition (flower stalk elongates), then the floral transition (first flower appears). Bolting is a robust predictor of flower formation, and hence a good indicator for vernalization research.

In winter annual Arabidopsis, vernalization of the meristem appears to confer competence to respond to floral inductive signals. A vernalized meristem retains competence for as long as 300 days in the absence of an inductive signal.

At the molecular level, flowering is repressed by the protein Flowering Locus C (FLC), which binds to and represses genes that promote flowering, thus blocking flowering. Winter annual ecotypes of Arabidopsis have an active copy of the gene FRIGIDA (FRI), which promotes FLC expression, thus repression of flowering. Prolonged exposure to cold (vernalization) induces expression of VERNALIZATION INSENSTIVE3, which interacts with the VERNALIZATION2 (VRN2) polycomb-like complex to reduce FLC expression through chromatin remodeling.{{cite journal

Since vernalization also occurs in flc mutants (lacking FLC), vernalization must also activate a non-FLC pathway.{{cite web |url= http://www.plant-biology.com/vernalisation-pathway-Arabidopsis.php |access-date=2011-01-26

Devernalization

It is possible to devernalize a plant by exposure to sometimes low and high temperatures subsequent to vernalization. For example, commercial onion growers store sets at low temperatures, but devernalize them before planting, because they want the plant's energy to go into enlarging its bulb (underground stem), not making flowers. cite encyclopedia | access-date = 2023-09-03

References

References

1. (1997). "Axenic seed culture and micropropagation of ''Cypripedium reginae''". Selbyana.
2. (2006). "Epigenetic maintenance of the vernalized state in Arabidopsis thaliana requires LIKE HETEROCHROMATIN PROTEIN 1". Nature Genetics.
3. (2015). "Plant Physiology and Development". Sinauer Associates.
4. (2003). "Attenuation of FLOWERING LOCUS C activity as a mechanism for the evolution of summer-annual flowering behavior in Arabidopsis". Proceedings of the National Academy of Sciences.
5. (1960). "Vernalization and its Relations to Dormancy". Annual Review of Plant Physiology.
6. (2015). "Applied Plant Genomics and Biotechnology". Woodhead Publishing.
7. (1985). "A new perspective on Lysenko?". Taylor & Francis.
8. (2004). "Vernalization, Competence, and the Epigenetic Memory of Winter". The Plant Cell.
9. (2010-05-06). "The conversion of spring wheat into winter wheat and vice versa: false claim or Lamarckian inheritance?". Journal of Biosciences.
10. (August 2007). "The molecular basis of vernalization-induced flowering in cereals". Elsevier.
11. (2009). "The significance of bolting and floral transitions as indicators of reproductive phase change in ''Arabidopsis''". Journal of Experimental Botany.
12. (2010). "Seasonal and developmental timing of flowering". The Plant Journal.
13. (2011). "The FRIGIDA Complex Activates Transcription ofFLC, a Strong Flowering Repressor in Arabidopsis, by Recruiting Chromatin Modification Factors". The Plant Cell.
14. (21 December 2018). "Oxygen-dependent proteolysis regulates the stability of angiosperm polycomb repressive complex 2 subunit VERNALIZATION 2.". Nature Communications.
15. (26 March 2025). "VRN2-PRC2 facilitates light-triggered repression of PIF signaling to coordinate growth in Arabidopsis". Developmental Cell.
16. http://www.jic.ac.uk/news/2014/10/plants-require-coolair-flower-spring {{Webarchive. link. (23 April 2015 {{full citation needed). (March 2016)
17. (2014). "Antisense COOLAIR mediates the coordinated switching of chromatin states atFLCduring vernalization". Proceedings of the National Academy of Sciences.
18. (2011). "Vernalization-Mediated Epigenetic Silencing by a Long Intronic Noncoding RNA". Science.
19. (2011). "A Polycomb-based switch underlying quantitative epigenetic memory". Nature.
20. (2014). "Epigenetic reprogramming that prevents trans-generational inheritance of the vernalized state". Nature.