Abstract
Cultivated hexaploid oat has three different sets of nuclear genomes (A, C, D), but its evolutionary history remains elusive. A multiplexed shotgun sequencing procedure was explored to acquire maternal phylogenetic signals from chloroplast and mitochondria genomes of 25 Avena species. Phylogenetic analyses of the acquired organelle SNP data revealed a new maternal pathway towards hexaploids of oat genome evolution involving three diploid species (A. ventricosa, A. canariensis and A. longiglumis) and two tetraploid species (A. insularis and A. agadiriana). Cultivated hexaploid A. sativa acquired its maternal genome from an AC genome tetraploid close to A. insularis. Both AC genome A. insularis and AB genome A. agadiriana obtained a maternal genome from an ancient A, not C, genome diploid close to A. longiglumis. Divergence dating showed the major divergences of C genome species 19.9–21.2 million years ago (Mya), of the oldest A genome A. canariensis 13–15 Mya, and of the clade with hexaploids 8.5–9.5 Mya. These findings not only advance our knowledge on oat genome evolution, but also have implications for oat germplasm conservation and utilization in breeding.
Highlights
Oat (Avena L., Poaceae family) is one of the most cultivated cereals worldwide and a valuable resource in several countries both for human consumption and animal feed[1]
Each sample for a given species had an average of 2,343,670 unique cp sequences and 106,063 mt sequences, giving a roughly 4300× cp genome coverage based on wheat cp genome length and 59 ×mt genome coverage based on wheat mt genome length
Al genome A. longiglumis was closely related to AB genome A. agadiriana based on cp data and to AC genome A. insularis based on mt data
Summary
Oat (Avena L., Poaceae family) is one of the most cultivated cereals worldwide and a valuable resource in several countries both for human consumption and animal feed[1]. Many experimental approaches have been applied with variable levels of success to search for informative phylogenetic signals for understanding oat evolution[10,12,18,19,20,21,22] They include ecotype analysis, interspecific crossing, cytogenetic analysis, gene-specific inference, and molecular marker application, and each approach has played a role in the inference of oat evolution[7]. Liu et al revealed an interesting evolutionary dynamics of ancient and recent polyploidization events in Avena based on three nuclear genes and three plastid genes[19] The specific objectives of this study were to elucidate maternal phylogenetic relationships of 25 Avena species, assess maternal pathway of A, C and D genomes towards hexaploid oat, and infer the history of major divergences in oat species
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