Nestor Kippes, Andrew Chen, Xiaoqin Zhang, Adam J. Lukaszewski, Jorge Dubcovsky

Theoretical and Applied Genetics; July 2016, Volume 129, Issue 7, pp 1417–1428

Abstract

Key message

The combination of three non-functional alleles of the flowering repressor VRN2 results in a spring growth habit in wheat.

Abstract

In temperate cereals with a winter growth habit, a prolonged exposure to low temperatures (vernalization) accelerates flowering. Before vernalization, the VRN2 locus plays a central role in maintaining flowering repression. Non-functional VRN2 alleles result in spring growth habit and are frequent in diploid wheat and barley. However, in hexaploid wheat, the effect of these non-functional VRN2 alleles is masked by gene redundancy. In this study, we developed a triple VRN2 mutant (synthetic vrn2-null) in hexaploid wheat by combining the non-functional VRN-A2 allele present in most polyploid wheats with a VRN-B2 deletion from tetraploid wheat, and a non-functional VRN-D2 allele from Aegilops tauschii (Ae. tauschii) (the donor of hexaploid wheat D genome). Non-vernalized vrn2-null plants flowered 118 days (P < 2.8E−07) earlier than the winter control, and showed a limited vernalization response. The functional VRN-B2 allele is expressed at higher levels than the functional VRN-D2 allele and showed a stronger repressive effect under partial vernalization (4 °C for 4 weeks), and also in non-vernalized plants carrying only a functional VRN-B2 or VRN-D2 in heterozygous state. These results suggest that different combinations of VRN-B2 and VRN-D2 alleles can be a used to modulate the vernalization response in regions with mild winters. Spring vrn2-null mutants have been selected repeatedly in diploid wheat and barley, suggesting that they may have an adaptative value and that may be useful in hexaploid wheat. Spring wheat breeders can use these new alleles to improve wheat adaptation to different or changing environments.

See http://link.springer.com/article/10.1007/s00122-016-2713-3/fulltext.html

Fig. 4

Effect of mutations in VRN-B2 and VRN-D2 on heading time under non vernalizing conditions. a Heading times for the triple mutant. Bars represent mean and error bars represent the SEM. Dashes represent mutant alleles, wt: wild type alleles and H: heterozygous. Lower doses of functional VRN2 were enough to significantly delay flowering. **P < 0.005 ***P < 0.001. Arrow indicates that the experiment was stopped before heading. b Maturity differences between the triple VRN2 mutant (left) and the wild type (right)