A study on the genetic relationships of Avena taxa and the origins of hexaploid oat

Abstract

Using next-generation DNA sequencing, it was possible to clarify the genetic relationships of Avena species and deduce the likely pathway from which hexaploid oat was formed by sequential polyploidization events. A sequence-based diversity study was conducted on a representative sample of accessions from species in the genus Avena using genotyping-by-sequencing technology. The results show that all Avena taxa can be assigned to one of four major genetic clusters: Cluster 1 = all hexaploids including cultivated oat, Cluster 2 = AC genome tetraploids, Cluster 3 = C genome diploids, Cluster 4 = A genome diploid and tetraploids. No evidence was found for the existence of discrete B or D genomes. Through a series of experiments involving the creation of in silico polyploids, it was possible to deduce that hexaploid oat likely formed by the fusion of an ancestral diploid species from Cluster 3 (A. clauda, A. eriantha) with an ancestral diploid species from Cluster 4D (A. longiglumis, A. canariensis, A. wiestii) to create the ancestral tetraploid from Cluster 2 (A. magna, A. murphyi, A. insularis). Subsequently, that ancestral tetraploid fused again with another ancestral diploid from Cluster 4D to create hexaploid oat. Based on the geographic distribution of these species, it is hypothesized that both the tetraploidization and hexaploidization events may have occurred in the region of northwest Africa, followed by radiation of hexaploid oat to its current worldwide distribution. The results from this study shed light not only on the origins of this important grain crop, but also have implications for germplasm collection and utilization in oat breeding.

Genomic relationships among sixteen species of Avena based on (ACT)6 trinucleotide repeat FISH

“…The first possibility is the fusion of ancestral C genome diploids with an ancestral A x genome diploid to create ancestral A x C tetraploids. Subsequently, the A x C tetraploids fused with ancestral A y diploids to create hexaploids (Chew et al 2016). The second possibility is that an ancient C genome and diverged A (D) diploid ancestors formed CD genome tetraploids and then hybridized with the more recent A genome diploid progenitors to form ACD genome hexaploids (Yan et al 2016a;Liu et al 2017).…”

“…longiglumis, A. canariensis, A. wiestii, A. strigosa, A. damascena, andA. lusitanica (Li et al 2000, 2009;Peng et al 2010;Luo et al 2014;Yan et al 2014;Chew et al 2016;Liu et al 2017). Probable C-genome ancestors include A.…”

“…Probable C-genome ancestors include A. clauda, A. eriantha, and A. ventricosa (Fominaya et al 1995;Chew et al 2016;Liu et al 2017). Probable diverged A (D)genome ancestors include A. longiglumis, A.…”

Phylogenetic relationships in the genus Avena based on the nuclear pgk1 gene

“…In the case of the B genome, an initial study of chromosome pairing of hybrids between the AB genome tetraploids and the A s genome diploids suggested that the B genome arose from the A s genome through autoploidization [23]. Recently, another GBS study [19] showed that the AB genome tetraploid species fell into a tight cluster with A s genome diploids, also supporting the hypothesis that the B genome arose through minor divergence following autoploidization. However, other evidence from C-banding [24], FISH [17], RAPD markers [25], and DNA sequence alignment [14] has indicated a clear distinction between A and B genomes, suggesting an allotetraploid origin of the AB genome tetraploid species.…”

“…Most research based on karyotype comparisons [6, 15], in situ hybridization [11, 16–18], as well as the alignments of nuclear genes [13, 14] suggest that one of the A s genome species may be the A genome donor of polyploid oats. Alternatively, some studies have proposed the A c genome diploid A. canariensis [19], or the A l genome diploid A. longiglumis [9, 12] as the most likely A genome donor.…”