Molecular evolution of receptor-like kinase genes in hexaploid wheat. Independent evolution of orthologs after polyploidization and mechanisms of local rearrangements at paralogous loci

Hexaploid wheat is a young polyploid species and represents a good model to study mechanisms of gene evolution after polyploidization. Recent studies at the scale of the whole genome have suggested rapid genomic changes after polyploidization but so far the rearrangements that have occurred in terms of gene content and organization have net been analyzed at the microlevel in wheat. Here, we have isolated members of a receptor kinase (Lrk) gene fa mily in hexaploid and diploid wheat, Aegilops tauschii, and barley (Hordeum vulgare). Phylogenetic analysis has allowed us to establish evolutionary r elationships (orthology versus paralogy) between the different members of t his gene family in wheat as well as with Lrk genes from barley. II also dem onstrated that the sequences of the homoeologous LI li genes evolved indepe ndently after polyploidization. in addition, we found evidence for gene las s during the evolution of wheat and barley. Analysis of large genomic fragm ents isolated from nonorthologous Lrk loci showed a high conservation of th e gene content and gene organization at these loci on the homoeologous grou p 1 chromosomes of wheat and barley. Finally, sequence comparison of two pa ralogous fragments of chromosome 1B showed a large number of local events ( sequence duplications, deletions, and insertions!, which reveal rearrangeme nts and mechanisms for genome enlargement at the microlevel.