Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2005
Publication Date: 8/1/2005
Citation: Loukoinov, A., Yan, L., Blechl, A.E., Sanchez, A., Dubcovsky, J. 2005. Regulation of vrn-1 vernalization genes in normal and transgenic polyploid wheat. Journal of Plant Physiology. Vol. 138, P. 1-10. Interpretive Summary: An important agronomic characteristic of winter wheat is the requirement for a growth period in cold temperatures to ensure that flowering is efficient and synchronized. This requirement is called vernalization and is controlled by two genes named Vrn1 and Vrn2. This paper reports the application of molecular biology and biotechnology to test the hypothesis that expression of the normal Vrn1 gene controls the timing of flowering in bread and ancestral wheats. Measurements of Vrn1 transcript levels showed that their concentrations must reach a threshold level in order to trigger the transition from vegetative to reproductive development. In winter wheats, the Vrn1 gene is only transcribed after several months of leaf and tiller growth or after exposure to cold temperatures. Biotechnology was used to show that suppression of Vrn1 transcription delays flowering of a spring wheat. These results confirm that the Vrn1 gene is essential in controlling the initiation of flowering in wheat and most likely, in barley and other temperate grass crops. Understanding the genes and environmental signals that control flowering will result in strategies to lessen some of the constraints of grain production.
Technical Abstract: Vernalization, the requirement of a long exposure to low temperatures to accelerate flowering, is an essential adaptation of plants to cold winters. The vernalization gene VRN-1 plays an important role in this process in diploid (Triticum monococcum) and polyploid wheat (Triticum aestivum). We have recently shown that the diploid wheat VRN-Am1 gene was similar to the Arabidopsis thaliana APETALA1 meristem identity gene. We also suggested that dominant Vrn- Am1 alleles were the result of loss of function mutations in regulatory regions recognized by a VRN-1 repressor. This model predicts that only the dominant Vrn-1 allele will be transcribed in lines carrying both recessive and dominant alleles. Here, we confirm this prediction in young isogenic lines of hexaploid wheat carrying different dominant Vrn-A1, Vrn-B1, and Vrn-D1 alleles, and also in heterozygous VRN-1 diploid wheat plants. However, a few weeks later, transcripts from the recessive alleles were also detected in both the polyploid and heterozygous diploid spring plants. This result suggests that the dominant Vrn-1 allele or a gene regulated by VRN-1 is necessary to accelerate the transcription initiation of the recessive alleles in unvernalized plants. We also show here that the level of VRN-1 transcripts in early developmental stages is critical for flowering initiation. A reduction of VRN-1 transcript levels by RNA interference delayed apex transition to the reproductive stage, increased the number of leaves, and delayed heading time by 2-3 weeks. We hypothesize that the coordinated transcription of dominant and recessive alleles contributes to the VRN-1 transcript level threshold required to trigger the flowering response in polyploid wheat.