Format: ORAL

Mara ngeles Decena1, 2, Joanna Lusinska3, Rubn Sancho1, 2, Robert Hasterok3, Ernesto Prez-Collazos1, 2, Lus. A. Inda1, 4, Pilar Cataln1, 2

1 Departamento de Ciencias Agrarias y del Medio Natural. Escuela Politécnica Superior de Huesca. Universidad de Zaragoza. C/ Carretera de Cuarte Km 1. E-22071 Huesca. Spain. 2 Grupo de Bioquímica, Biofísica y Biología Computacional (BIFI, UNIZAR), Unidad Asociada al CSIC, E-50059 Zaragoza. Spain. 3 Plant Cytogenetics and Molecular Biology Group, Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, Katowice 40-032, Poland. 4 Instituto Agroalimentario de Aragón-IA2 (Universidad de Zaragoza-CITA), Aragón, Spain.

Descending dysploidy may be considered as one of the mechanisms that convert polyploids into functional diploids. However, karyotypes resulting from this mechanism can also be present in neopolyploids and diploids. The model grass genus Brachypodium contains up to 21 recognized species showing a remarkable descending dysploidy and various ploidy levels. We performed an extensive cyto-phylogenomic study of its 14 worldwide distributed perennial species and minor satellite taxa. Genome size, chromosome number, and comparative-chromosome-barcoding analyses across 147 populations revealed previously unknown cytotypes for several species and characterized the karyotypic profiles of their constituent genomes. A Brachypodium supertree showed the participation of ancestral orphan progenitor genomes in American B. mexicanum, ancestral and recent orphan and extant progenitor genomes with diverse basic chromosome numbers or karyotype structure in the aridic-to-mesic Mediterranean and Western European lineages (B. retusum, B. boissieri, B. phoenicoides,B. rupestre), and intermediate-recent extant progenitor genomes in currentlydiploid core-perennial mesic lineages (B. arbuscula-2x, B. sylvaticum-2x, B. pinnatum-2x). Phylogenetic inference suggested the rapid evolution of distinct descending dysploidy trends from ancestral (x=10) or intermediate (x=9) karyotypes to different sorts of derived karyotypes (x=8, x=6, x=5). Our hypothesized scenarios indicated that some of the descending dysploidies preceded both ancestral and recent polyploidizations (x=10-x=8[genome A2], x=10-x=9[G], x=10-x=5[D], x=9-x=8[E1], x=9-x=5[E2]) as these unique karyotypes correspond to orphan diploid progenitor genomes of current Brachypodium polyploids, while others likely occurred after the polyploidizations (x=8[A2]+8[E1]+5[E2]-x=8[A2]+6[E1]+5[E2]; x=9[G]+5[E2]+5[E2]->x=8[G’]+5[E2]+5[E2]), as they correspond to rare orphan subgenomes of some allopolyploids. Our analysis uncovered another recent descending dysploidy (x=9[G]->x=8[G*]) occurring in parallel in closely diverging diploid lineages. Most of the descending dysploidies detected in Brachypodium resulted from nested chromosome fusions, while just a few were caused by telomeric fusions. The different combinations of these ‘orphan’ and ‘extant’ dysploid genomes originated diverse phenotypic differences among species and cytotypes.