Combining promoter and induced intron 1 mutations of Vrn-A1a does not accelerate flowering in wheat

In temperate cereals, vernalization regulates the transition from vegetative to reproductive growth in response to low temperatures. A central component of this pathway is VERNALIZATION 1 (VRN1). In winter wheat cultivars, the recessive vrn1 allele is transcriptionally activated by cold and promotes the transition to flowering. In contrast, spring cultivars carry dominant VRN1 alleles expressed in a cold-independent manner. This is caused by mutations in the cis-regulatory elements in the promoter or in the "critical region" of intron 1. The widespread spring bread wheat allele Vrn-A1a carries a promoter mutation but retains a winter-like allele intron 1. Intriguingly, Vrn-A1a is partially responsive to cold, suggesting regulatory element(s) beyond the promoter mutation. Here, we investigated the effect of combined promoter and first intron mutations on Vrn-A1a expression and flowering time in bread wheat. We deleted a 901-bp segment of the Vrn-A1a so-called "critical region", thus generating a novel combination of the promoter and intron 1 mutations not found in natural germplasm. Plants carrying both mutations exhibited Vrn-A1 transcript levels and flowering times comparable to those of the wild-type under both vernalizing and non-vernalizing conditions. Hence, partial cold responsiveness of Vrn-A1a is controlled by regulatory element(s) outside the removed intron 1 segment. Overall, our study advances the understanding of VRN1 transcriptional regulation and highlights the complexity of vernalization control in wheat.

The online version contains supplementary material available at 10.1007/s11032-026-01657-6.