Genome composition and origin of the polyploid Aegean grass Avenula agropyroides (Poaceae)

Aim The Aegean is a hotspot of plant biodiversity, with its island biota harbouring a large number of endemic taxa. To investigate the relationship between biogeography, polyploid speciation and genomics in the Aegean we used the biogeographically isolated highly polyploid eastern Mediterranean grass species Avenula agropyroides (2n = 70) as an example of complicated polyploid origin. Location Mediterranean, Aegean. Methods To clarify the origin of A. agropyroides, we conducted chromosome studies using repetitive DNAs as hybridization probes in fluorescent in situ hybridization experiments, chromosome banding methods and DNA sequence analyses of plasmid‐cloned nuclear ribosomal (nr) ITS1–5.8S–ITS2 DNA. Results Decaploid A. agropyroides had near‐autopolyploid karyotype structure and contained characteristic sequence motifs of nrDNA repeats not encountered in any of the diploids studied. Special repeat types found in one of its accessions (Crete) showed that A. agropyroides originated from a diploid species with a hybrid background. One of the genomes involved was close to both that of extant species (Avenula aetolica, Avenula compressa, Avenula hookeri, Avenula schelliana, Avenula versicolor) distributed mostly in the eastern Mediterranean to Asia and North America and also to the west Mediterranean (Avenula bromoides). The other resembled that of exclusively western Mediterranean species (Avenula albinervis, Avenula levis, Avenula marginata, Avenula sulcata). Main conclusions Avenula agropyroides represents a remarkable polyploid in the eastern Mediterranean, conserving the genome structure of a diploid species that no longer exists. This highlights how the Aegean has been less affected than other Eurasian regions by the repeated shifts of climatic zones and vegetation belts since the Late Tertiary.