Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2006
Publication Date: 12/19/2006
Citation: Yan, L., Fu, D., Li, C., Blechl, A.E., Tranquilli, G., Bonafede, M., Sanchez, A.N., Valarik, M., Yasuda, S., Dubcovsky, J. 2006. The wheat and barley vernalization gene VRN3 is an orthologue of FT. Proceedings of the National Academy of Sciences. 103: 19581-19586 Interpretive Summary: Wheat and barley are cereal crops grown in many different temperate environments worldwide. “Winter” wheat and barley varieties require extended periods of exposure to low temperatures to accelerate flowering (vernalization), whereas “spring” varieties do not have this requirement. The research in this paper was aimed at isolating and sequencing a gene called Vernalization 3 or VRN3 that determines whether a variety requires vernalization for synchronous efficient flowering, i.e. whether a variety is a spring or a winter wheat. The VRN3 gene encodes a signal molecule that promotes flowering. When it is functional, the plant does not require vernalization. Winter varieties carry non-functional mutations in this gene and thus require vernlization to activate the flowering pathway. Increasing expression of VRN3 in a winter wheat by genetic transformation accelerated flowering by more than 60 days. The isolation and characterization of this gene gives breeders a new tool with which they can vary heading times and ensure optimum flowering for different wheat and barley varieties grown under different climate conditions.
Technical Abstract: Winter wheat and barley varieties require an extended exposure to low temperatures to accelerate flowering (vernalization), whereas spring varieties do not have this requirement. In this study, we show that in these species the vernalization gene VRN3 is completely linked to a gene similar to Arabidopsis FLOWERING LOCUS T (FT). FT induction in the leaves results in a transmissible signal that promotes flowering. Transcript levels of the barley and wheat orthologues, designated as HvFT and TaFT respectively, are significantly higher in plants homozygous for the dominant Vrn3 alleles (early flowering) than in plants homozygous for the recessive vrn3 alleles (late flowering). In wheat, the dominant Vrn3 allele is associated with the insertion of a retroelement in the TaFT promoter, whereas in barley, mutations in the HvFT first intron differentiate plants with dominant and recessive VRN3 alleles. Winter wheat plants transformed with the TaFT allele carrying the promoter retroelement insertion flowered significantly earlier than non-transgenic plants, supporting the identity between TaFT and VRN-B3. Statistical analyses of flowering times confirmed the presence of significant interactions between vernalization and FT allelic classes in both wheat and barley (P<0.0001). These interactions were further supported by the observed up-regulation of HvFT transcript levels by vernalization in barley winter plants (P=0.002). These results confirmed that the wheat and barley FT genes are responsible for natural allelic variation in vernalization requirement, providing additional sources of adaptive diversity to these economically important crops.