Molecular Characterization of Sec2 Loci in Wheat—Secale africanum Derivatives Demonstrates Genomic Divergence of Secale Species

The unique 75 K γ-secalins encoded by Sec2 loci in Secale species is composed of almost half rye storage proteins. The chromosomal location of Sec2 loci in wild Secale species, Secale africanum, was carried out by the wheat—S. africanum derivatives, which were identified by genomic in situ hybridization and multi-color fluorescence in situ hybridization. The Sec2 gene-specific PCR analysis indicated that the S. cereale Sec2 was located onchromosome 2R, while the S. africanum Sec2 was localized on chromosome 6R(afr) of S. africanum. A total of 38 Sec2 gene sequences were isolated from S. africanum, S. cereale and S. sylvestre by PCR-based cloning. Phylogenetic analysis showed that S. africanum Sec2 diverged from S. cereale Sec2 approximately 2–3 million years ago. The illegitimate recombination of chromosome 2R–6R involving the Sec2 loci region may accelerate sequence variation during evolutionary process from wild to cultivated Secale species.