Vernalization promotes flowering in winter wheat cultivars, whereas spring wheat cultivars are able to transition from vegetative to reproductive phase without vernalization. The wheat vernalization requirement is mainly controlled by the major locus Vrn-1, an APETALA1/FRUITFULL MADS-box gene homolog. To study natural variation of the vernalization requirement in a wild progenitor of common wheat, we sequenced the Vrn-D(t)1 locus in four accessions of Aegilops tauschii Coss. Some structural mutations were found in the promoter and first intron regions of Vrn-D(t)1, and haplotype analysis was conducted to examine the distribution of each identified mutation within 211 accessions of Ae. tauschii germplasm. Out of the total, nine accessions, which were originally collected in Afghanistan and Pakistan, contained deletions of a 5.4-kb sequence in the critical region of the Vrn-D(t)1 first intron. The 5.4-kb deletion mutation appeared independently of the dominant allele of the common wheat Vrn-D1 locus. The large deletion was absolutely associated with a lack of vernalization requirement for flowering under long-day conditions, but had no influence on heading date under field growth conditions. The levels of Vrn-1 and WFT transcript increased in the Ae. tauschii accessions having the large deletion. Identification of natural mutant accessions with a loss of vernalization requirement indicates the agricultural significance of Ae. tauschii as a genetic resource for wheat breeding.
Control of fl owering time is an adaptive trait of plants for different growth habitats. A vernalization requirement is a major genetic component determining wheat fl owering time. Arabidopsis VERNALIZATION INSENSITIVE3 ( VIN3 ) and VIN3-like 1 ( VIL1 ) play critical roles in the vernalization pathway of fl owering, and three wheat VIL homologs are upregulated by vernalization in einkorn wheat. To study the relationship between vernalization and wheat VIL homologs in Aegilops tauschii , the D-genome progenitor of common wheat, we isolated three cDNAs orthologous to the einkorn wheat VIL genes. The three Ae. tauschii VIL genes showed many single nucleotide polymorphisms including non-synonymous substitutions relative to the einkorn orthologs. In addition, high rates of non-synonymous and synonymous substitutions were revealed by intraspecifi c variation analysis of the AetVIL sequences, suggesting adaptive evolution at the AetVIL loci. Quantitative RT-PCR analysis was conducted to examine the time course of expression of the VIL genes during vernalization. Of the three AetVIL genes, AetVIL2 was upregulated after one week of lowtemperature treatment, and its expression pattern was distinct for winter and spring habit accessions. These observations strongly suggest that AetVIL2 is associated with the vernalization-responsive pathway in Ae. tauschii .
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