Rye Subgenome Suppression in Triticale: An Insight into Genome Restructuring in Recent Polyploids

The synthetic polyploid species triticale which is derived from wheat (Triticum turgidum) and rye (Secale cereale) is an excellent model to study the rapid genome evolution that occurs in plants after polyploidization events.  High through-put cDNA sequence comparison between the diploid rye and the hexaploid triticale detected suppression of expression of approximately 0.5% of rye genes surveyed in the triticale background.  The expression of 23503 rye cDNA contig assemblies was analyzed in 454-cDNA libraries obtained from anther, root and stem from both triticale and rye as well as in five 454-cDNA data sets created from ovary, pollen, seed, seedling shoot and stigma from triticale.  Among these, 112 rye cDNA contigs were found to be totally suppressed in all triticale tissues, although their expressions were relatively high in rye tissues. Interestingly, the average DNA sequence identity between rye genes that were suppressed in triticale and their most similar contig in the Triticum A and B genomes was only 82%.  This degree of similarity is significantly lower than the global average similarity between rye genes and their Triticum A and B homeologs which was found to be 95% identity in a test set of 330 triticale genes.