Marker Assisted Selection in Wheat - HOME USDA National Institute of Food and Agriculture The Borlaug Global Rust Initiative Marker Assisted Selection in Wheat

Abiotic Stress and Agronomic Traits

Vernalization requirement

Background information

Winter wheat varieties require an extended exposure to cold temperatures to induce flowering, a process called vernalization, while spring varieties do not have such a requirement. Typical vernalization conditions are 4 to 6 weeks at less than 10°C. The need for vernalization is an adaptation of several cereals, not only wheat, to cold climates. Flowers will only start developing once the risk of damage caused by cold is minimal.

Vernalization in cultivated wheat is mainly controlled by three VRN1 loci, VRN-A1, VRN-B1 and VRN-D1, located in the middle of the long arms of chromosomes 5A, 5B and 5D, respectively (1). Winter cultivars are homozygous for the recessive alleles at the three VRN-1 loci. (2). The VRN-1 gene was initially cloned in Triticum monococcum (3), and later polymorphisms in the VRN1 promoter (4) and intron regions (5) associated with spring growth habit were described in common and durum wheat.

A number of allelels were reported for the major vernalization gene Vrn-A1.

  • vrn-A1: recessive allele
  • Vrn-A1a is the most potent spring allele, causing complete insensitivity to vernalization. It has an insertion of a foldback repetitive element and a duplicated region in the promoter
  • Vrn-A1b allele shows several SNPs and deletions in the promoter region, tipically a 20-bp deletion in the 5’ untranslated region
  • Vrn-A1c allele has a large deletion in the first intron. This allele was found only in the spring hexaploid landrace IL369 from Afghanistan, but is common among tetraploid spring genotypes
  • Vrn-A1d: 32-bp deletion in the promoter region
  • Vrn-A1e: 54-bp deletion in the promoter region, typical of spring tetraploids wheats

The alleles for spring growth habit discovered so far for both Vrn-B1 Vrn-D1 have large deletions in the first intron.

Vrn-B3, located on chromosome arm 7BS, was first reported when a dominant allele for spring growth habit was identified in the cultivar Hope. This dominant allele has a retrotransposon insertion in the promoter region of a gene similar to Arabidopsis FT (8).

Another gene important for vernalization is VRN2 (1,6) which is a long day flowering repressor of VRN3 . Two genes are present at the VRN2 locus (ZCCT1 and ZCCT2 ) and deletions or non-functional mutations in both of them simultaneously are associated with spring growth habit in both diploid what (1) and tetraploid wheat (9)

Methods

The methods section lists markers useful to characterize the different VRN-1 alleles and Vrn-B3. These markers amplify sequences in two specific regions, the promoter and the first intron, where a series of insertions, deletions and duplications account for the different alleles discovered.

Available germplasm

The papers published by Yan et al .(4) and Fu et al. (5) have extensive lists of germplasm from different origins with indications of growth habit and genotype.

References

1. Catalogue of Gene Symbols for Wheat. McIntosh RA, Yamazaki Y, Devos KM, Dubcovsky J, Rogers WJ, Appels R . In: Pogna NE, Romano M, Pogna E, Galterio G (eds) Proceedings of the 10th International Wheat Genetics Symposium. Instituto Sperimentale per la Cerealicoltura, Rome, Paestum, Italy.
http://wheat.pw.usda.gov/ggpages/wgc/2003/

2. Growth habit in common wheat (Triticum aestivum L. EM. Thell.). Stelmakh AF. In: Euphytica, 1987, 36:513-519. [abstract]

3. Positional cloning of the wheat vernalization gene VRN1. Yan L, Loukoianov A, Tranquilli G, Helguera M, Fahima T, Dubcovsky J. In: Proceedings of the National Academy of Sciences, 2003,100:6263-6268. [abstract]

4. Allelic variation at the VRN-1 promoter region in polyploid wheat. Yan L, Helguera M, Kato K, Fukuyama S, Sherman J, Dubcovsky J. In: Theoretical and Applied Genetics, 2004, 109:1677-1686. [abstract]

5. Large deletions within the VRN-1 first intron are associated with spring growth habit in barley and wheat. Fu D, Szücs P, Yan L, Helguera M, Skinner JS, Zitzewitz J, Hayes PM, Dubcovsky J. In: Molecular Geentics and Genomics, 2005, 273:54-65. [abstract]

6. The wheat VRN2 gene is a flowering repressor down-regulated by vernalization. Yan L, Loukoianov A, Blechl A, Tranquilli G, Ramakrishna W, SanMiguel P, Bennetzen JL, Echenique V, Dubcovsky J. In: Science, 2004, 303:1640-1644. [abstract]

7. A PCR marker for growth habit in common wheat based on allelic variation at the VRN-A1 gene. Sherman JD, Yan L, Talbert L, Dubcovsky J. In: Crop Science, 2004, 44:1832-1838. [abstract]

8. The wheat and barley vernalization gene VRN3 is an orthologue of FT. Yan L, Fu D, Li C, Blechl A, . Tranquilli G, Bonafede M, Sanchez A, Valarik M, Dubcovsky J. 2006. In: Proceeding of the National Academy of Sciences. U.S.A. 103:19581-19586. [abstract]

9. Genetic and molecular characterization of the VRN2 loci in tetraploid wheat. Distelfeld A, Tranquilli G, Li C, Yan L, Dubcovsky J. In: Plant Physiology 2009 In press.

Back to top