Vernalization

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Many species of henbane require vernalization before flowering. Hyoscyamus niger Hullukaali Bolmort C IMG 7657.JPG
Many species of henbane require vernalization before flowering.

Vernalization (from Latin vernus  'of the spring ') is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower, but they may require additional seasonal cues or weeks of growth before they will actually do so. The term is sometimes used to refer to the need of herbal (non-woody) plants for a period of cold dormancy in order to produce new shoots and leaves, [1] but this usage is discouraged. [2]

Contents

Many plants grown in temperate climates require vernalization and must experience a period of low winter temperature to initiate or accelerate the flowering process. This ensures that reproductive development and seed production occurs in spring and winters, rather than in autumn. [3] The needed cold is often expressed in chill hours. Typical vernalization temperatures are between 1 and 7 degrees Celsius (34 and 45 degrees Fahrenheit). [4]

For many perennial plants, such as fruit tree species, a period of cold is needed first to induce dormancy and then later, after the requisite period of time, re-emerge from that dormancy prior to flowering. Many monocarpic winter annuals and biennials, including some ecotypes of Arabidopsis thaliana [5] and winter cereals such as wheat, must go through a prolonged period of cold before flowering occurs.

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. [6]

In 1928, the Soviet agronomist Trofim Lysenko published his works on the effects of cold on cereal seeds, and coined the term "яровизация" ("jarovization") to describe a chilling process he used to make the seeds of winter cereals behave like spring cereals (Jarovoe in Russian, originally from jar meaning fire or 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". [7]

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. [8] 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. [9] 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." [10]

Early research on vernalization focused on plant physiology; the increasing availability of molecular biology has made it possible to unravel its underlying mechanisms. [9] 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). [11]

In Arabidopsis thaliana

Arabidopsis thaliana rosette before vernalization, with no floral spike Arabidopsis thaliana rosette.png
Arabidopsis thaliana rosette before vernalization, with no floral spike

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. [12] [ self-published source? ] The genes that underlie this difference in plant physiology have been intensively studied. [9]

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). [13] Bolting is a robust predictor of flower formation, and hence a good indicator for vernalization research. [13]

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. [12]

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. [3] [14] Winter annual ecotypes of Arabidopsis have an active copy of the gene FRIGIDA (FRI), which promotes FLC expression, thus repression of flowering. [15] 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. [16] Levels of VRN2 protein increase during long-term cold exposure as a result of inhibition of VRN2 turnover via its N-degron. [17] The events of histone deacetylation at Lysine 9 and 14 followed by methylation at Lys 9 and 27 is associated with the vernalization response. The epigenetic silencing of FLC by chromatin remodeling is also thought to involve the cold-induced expression of antisense FLC COOLAIR [18] [19] or COLDAIR transcripts. [20] Vernalization is registered by the plant by the stable silencing of individual FLC loci. [21] The removal of silent chromatin marks at FLC during embryogenesis prevents the inheritance of the vernalized state. [22]

Since vernalization also occurs in flc mutants (lacking FLC), vernalization must also activate a non-FLC pathway. [23] [ self-published source? ] A day-length mechanism is also important. [11] Vernalization response works in concert with the photo-periodic genes CO, FT, PHYA, CRY2 to induce flowering.

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. [24]

See also

Related Research Articles

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<i>Arabidopsis thaliana</i> Model plant species in the family Brassicaceae

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<span class="mw-page-title-main">Trofim Lysenko</span> Soviet agronomist and pseudo-scientist (1898–1976)

Trofim Denisovich Lysenko was a Soviet agronomist and pseudoscientist. He was a strong proponent of Lamarckism, and rejected Mendelian genetics in favour of his own idiosyncratic, pseudoscientific ideas later termed Lysenkoism.

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<span class="mw-page-title-main">Antisense RNA</span>

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<span class="mw-page-title-main">Repressor</span> Sort of RNA-binding protein in molecular genetics

In molecular genetics, a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA. An RNA-binding repressor binds to the mRNA and prevents translation of the mRNA into protein. This blocking or reducing of expression is called repression.

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<span class="mw-page-title-main">Caroline Dean</span> British botanist

Dame Caroline Dean is a British plant scientist working at the John Innes Centre. She is focused on understanding the molecular controls used by plants to seasonally judge when to flower. She is specifically interested in vernalisation — the acceleration of flowering in plants by exposure to periods of prolonged cold. She has also been on the Life Sciences jury for the Infosys Prize from 2018.

<span class="mw-page-title-main">PRC2</span>

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Flowering Locus C (FLC) is a MADS-box gene that in late-flowering ecotypes of the plant Arabidopsis thaliana is responsible for vernalization. In a new seedling FLC is expressed, which prevents flowering. Upon exposure to cold, less FLC is expressed, and flowering becomes possible. FLC is extensively regulated through epigenetic modifications and transcriptional control.

Richard Arthur is a professor of biochemistry and genetics at the University of Wisconsin-Madison. He got his bachelor's degree in biology at Pennsylvania State University. He went on to receive his PhD in biochemistry at Indiana University in 1982 and did post doctoral research at the University of Washington. Amasino's research focuses on plants and how plants know when to flower. In 2006 he was elected to the National Academy of Sciences.

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Elizabeth Jean Finnegan FAA is an Australian botanist who researches plant flowering processes and epigenetic regulation in plants. She currently works at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) as a senior scientist, leading research on the "Control of Floral Initiation", part of the CSIRO Agriculture Flagship.

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Plants depend on epigenetic processes for proper function. Epigenetics is defined as "the study of changes in gene function that are mitotically and/or meiotically heritable and that do not entail a change in DNA sequence". The area of study examines protein interactions with DNA and its associated components, including histones and various other modifications such as methylation, which alter the rate or target of transcription. Epi-alleles and epi-mutants, much like their genetic counterparts, describe changes in phenotypes due to epigenetic mechanisms. Epigenetics in plants has attracted scientific enthusiasm because of its importance in agriculture.

Robert J. Schmitz is an American plant biologist and epigenomicist at the University of Georgia where he studies the generation and phenotypic consequences of plant epialleles as well as developing new techniques to identify and study cis-regulatory sequences. He is an associate professor in the department of genetics and the UGA Foundation Endowed Pant Sciences Professor.

<span class="mw-page-title-main">RNA-directed DNA methylation</span> RNA-based gene silencing process

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References

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  3. 1 2 Sung, Sibum; He, Yuehui; Eshoo, Tifani W; Tamada, Yosuke; Johnson, Lianna; Nakahigashi, Kenji; Goto, Koji; Jacobsen, Steve E; Amasino, Richard M (2006). "Epigenetic maintenance of the vernalized state in Arabidopsis thaliana requires LIKE HETEROCHROMATIN PROTEIN 1". Nature Genetics. 38 (6): 706–10. doi:10.1038/ng1795. PMID   16682972. S2CID   2855447.
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  10. ↑ Li, Xiuju; Liu, Yongsheng (6 May 2010). "The conversion of spring wheat into winter wheat and vice versa: false claim or Lamarckian inheritance?". Journal of Biosciences. 35 (2): 321–325. doi:10.1007/s12038-010-0035-1. ISSN   0250-5991. PMID   20689187. S2CID   10527354.
  11. 1 2 Trevaskis, Ben; Hemming, Megan N.; Dennis, Elizabeth S. (August 2007). "The molecular basis of vernalization-induced flowering in cereals". Trends in Plant Science. Elsevier. 12 (8): 352–357. doi:10.1016/j.tplants.2007.06.010. PMID   17629542.
  12. 1 2 "Vernalisation response". Plant Biology. Retrieved 26 January 2011.[ self-published source ]
  13. 1 2 Pouteau, Sylvie; Albertini, Catherine (2009). "The significance of bolting and floral transitions as indicators of reproductive phase change in Arabidopsis". Journal of Experimental Botany. 60 (12): 3367–77. doi: 10.1093/jxb/erp173 . PMID   19502535.
  14. ↑ Amasino, Richard (2010). "Seasonal and developmental timing of flowering". The Plant Journal. 61 (6): 1001–13. doi: 10.1111/j.1365-313X.2010.04148.x . PMID   20409274.
  15. ↑ Choi, Kyuha; Kim, Juhyun; Hwang, Hyun-Ju; Kim, Sanghee; Park, Chulmin; Kim, Sang Yeol; Lee, Ilha (2011). "The FRIGIDA Complex Activates Transcription ofFLC, a Strong Flowering Repressor in Arabidopsis, by Recruiting Chromatin Modification Factors". The Plant Cell. 23 (1): 289–303. doi:10.1105/tpc.110.075911. PMC   3051252 . PMID   21282526.
  16. ↑ Sung, Sibum; Amasino, Richard M. (2004). "Vernalization in Arabidopsis thaliana is mediated by the PHD finger protein VIN3". Nature. 427 (6970): 159–163. Bibcode:2004Natur.427..159S. doi:10.1038/nature02195. PMID   14712276. S2CID   4418494.
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  18. ↑ http://www.jic.ac.uk/news/2014/10/plants-require-coolair-flower-spring Archived 23 April 2015 at the Wayback Machine [ full citation needed ]
  19. ↑ Csorba, Tibor; Questa, Julia I.; Sun, Qianwen; Dean, Caroline (2014). "Antisense COOLAIR mediates the coordinated switching of chromatin states atFLCduring vernalization". Proceedings of the National Academy of Sciences. 111 (45): 16160–5. Bibcode:2014PNAS..11116160C. doi: 10.1073/pnas.1419030111 . PMC   4234544 . PMID   25349421.
  20. ↑ Heo, J. B.; Sung, S. (2011). "Vernalization-Mediated Epigenetic Silencing by a Long Intronic Noncoding RNA". Science. 331 (6013): 76–9. Bibcode:2011Sci...331...76H. doi:10.1126/science.1197349. PMID   21127216. S2CID   19127414.
  21. ↑ Angel, Andrew; Song, Jie; Dean, Caroline; Howard, Martin (2011). "A Polycomb-based switch underlying quantitative epigenetic memory". Nature. 476 (7358): 105–8. doi:10.1038/nature10241. PMID   21785438. S2CID   205225603.
  22. ↑ Crevillén, Pedro; Yang, Hongchun; Cui, Xia; Greeff, Christiaan; Trick, Martin; Qiu, Qi; Cao, Xiaofeng; Dean, Caroline (2014). "Epigenetic reprogramming that prevents trans-generational inheritance of the vernalized state". Nature. 515 (7528): 587–90. Bibcode:2014Natur.515..587C. doi:10.1038/nature13722. PMC   4247276 . PMID   25219852.
  23. ↑ "Vernalisation pathway". Plant Biology. Retrieved 26 January 2011.[ self-published source ]
  24. ↑ "Vernalization". Encyclopædia Britannica Online. Retrieved 3 September 2023. Devernalization can be brought about by high temperatures ... Onion sets ... are ... ready to flower ... temperatures above 26.7 °C (80 °F) ..., however, shifts the sets to the desired bulb-forming phase.
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