Differences between diploid donors are the main contributing factor for subgenome asymmetry measured in either gene ratio or relative diversity in allopolyploids

Introduction Polyploidy, forming new species by enveloping two or more genomes within a single nucleus, is a prominent speciation process. Previous studies show that polyploidization was likely involved in the [...]
Subgenome asymmetry (SA) has routinely been attributed to different responses between the subgenomes of a polyploid to various stimuli during evolution. Here, we compared subgenome differences in gene ratio and relative diversity between artificial and natural genotypes of several allopolyploid species. Surprisingly, consistent differences were not detected between these two types of polyploid genotypes, although they differ in times exposed to evolutionary selection. The estimated ratio of shared genes between a subgenome and its diploid donor was invariably higher for the artificial allopolyploid genotypes than those for the natural genotypes, which is expected as it is now well-known that many genes in a species are not shared among all individuals. As the exact diploid parent for a given subgenome is unknown, the estimated ratios of shared genes for the natural genotypes would also include difference among individual genotypes of the diploid donor species. Further, we detected the presence of SA in genotypes before the completion of the polyploidization events as well as in those which were not formed via polyploidization. These results indicate that SA may, to a large degree, reflect differences between its diploid donors or that changes occurred during polyploid evolution are defined by their donor genomes. Key words: asymmetric evolution, subgenome asymmetry, diploid donor, polyploids, progenitor. L'asymetrie des sous-genomes (AS) est generalement attribuee a l'acquisition, au cours de l ' evolution, de reponses differentes a divers stimuli entre les sous-genomes presents chez un polyploide. Dans ce travail, les auteurs ont compare les differences entre sous-genomes pour ce qui est du ratio de genes et de la diversite relative entre genotypes naturels et artificiels chez plusieurs especes allopolyploides. Etonnamment, des differences ont regulierement n'ont pas ete detectees entre ces deux types de genotypes polyploides bien qu'ils different dans la duree de leur exposition a la selection. Le ratio estime de genes partages entre un sous-genome et le genome de l'espece ancestrale etait invariablement plus eleve chez les allopolyploides artificiels que chez les genotypes naturels, un resultat attendu puisqu'il est bien connu que plusieurs genes ne sont pas presents chez tous les individus d'une espece. Comme le parent diploide exact n'est pas connu pour un sous-genome donne, les ratios estimes de genes partages avec les genotypes naturels pourraient egalement inclure des differences entre genotypes distincts de l'espece diploide ancestrale. De plus, les auteurs ont detecte la presence dAS chez des genotypes avant le terme de la polyploidisation de meme que chez ceux qui n' etaient pas issus de la polyploidisation. Ces resultats indiquent que l 'AS pourrait, en grande partie, refleter des differences entre les especes diploides ancestrales ou que les changements survenus au cours de l ' evolution des polyploides sont definis par les genomes ancestraux. [Traduit par la Redaction] Mots-cles : evolution asymetrique, asymetrie des sous-genomes, diploide ancestral, polyploide, progeniteur.