Plant Paleogenomics Unveils New Evidences of Contrasted Evolutionary Plasticity Between Polyploidy-Driven Subgenomes

During the last decade, technological improvements led to the development of large sets of plant genomic resources permitting the emergence of high-resolution comparative genomic studies, pre-requisite for the reconstruction of extinct ancestral genomes of modern species, i.e. paleogenomics. By conducting detailed analysis of the length, composition, and divergence time of the conserved/duplicated blocks, we identified common and lineage-specific patterns of conservation between the different plant genomes that allowed us to propose a model in which the flowering plants have evolved from common ancestors with a basic number of five/seven protochromosomes containing ~10000 ordered protogenes through ancestral whole genome duplications (i.e. paleopolyploidization) and translocations followed by lineage specific segmental duplications, chromosome fusions and translocations.

Bread wheat derives from a grass ancestor structured in 7 protochromosomes followed by a paleotetraploidization to reach a 12 chromosomes intermediate and a neohexaploidization (involving subgenomes A, B and D) event that finally shaped the 21 modern chromosomes. Insights into wheat syntenome in sequencing COS (Conserved Orthologous Set) genes unravelled differences in genomic structure (such as gene conservation and diversity) and genetical landscape (such as recombination pattern) between ancestral as well as recent duplicated blocks. Contrasted evolutionary plasticity is observed where the B subgenome appears more sensitive (i.e. plastic) in contrast to A as dominant (i.e. stable) in response to the neotetraploidization and D subgenome as supradominant (i.e. pivotal) in response to the neohexaploidization event. Consequences of such contrasted plasticity between paleo- as well as neo-duplicated chromosomes during flowering plant evolution will be discussed.