Unraveling the evolutionary dynamics of ancient and recent polyploidization events in Avena (Poaceae)

Qing Liu,Paul M Peterson,Lei Lin,Jun Wen,Xiangying Zhou

doi:10.1038/srep41944

Abstract

Understanding the diversification of polyploid crops in the circum-Mediterranean region is a challenging issue in evolutionary biology. Sequence data of three nuclear genes and three plastid DNA fragments from 109 accessions of Avena L. (Poaceae) and the outgroups were used for maximum likelihood and Bayesian analyses. The evolution of cultivated oat (Avena sativa L.) and its close relatives was inferred to have involved ancient allotetraploidy and subsequent recent allohexaploidy events. The crown ages of two infrageneric lineages (Avena sect. Ventricosa Baum ex Romero-Zarco and Avena sect. Avena) were estimated to be in the early to middle Miocene, and the A. sativa lineages were dated to the late Miocene to Pliocene. These periods coincided with the mild seasonal climatic contrasts and the Mediterranean climate established in the Mediterranean Basin. Our results suggest that polyploidy, lineage divergence, and complex reticulate evolution have occurred in Avena, exemplifying the long-term persistence of tetraploids and the multiple origins of hexaploids related to paleoclimatic oscillations during the Miocene-Pliocene interval in the circum-Mediterranean region. This newly-resolved infrageneric phylogenetic framework represents a major step forward in understanding the origin of the cultivated oat.

Highlights

Cultivated oat offers a model for unraveling the dynamic evolutionary process of polyploid crops in the Mediterranean Basin[15]
Initial study of repeat sequences indicated that A. strigosa Schreb
The origin of western Mediterranean dated to the Eocene (35 million years ago, mya), and the eastern Mediterranean was formed during the mid-Miocene (16 mya) by collision of Arabian and Eurasian tectonic plates, which led to the configuration of the modern Mediterranean Basin[26]

Summary

Introduction

Cultivated oat offers a model for unraveling the dynamic evolutionary process of polyploid crops in the Mediterranean Basin[15]. DNA was homologous to the A-genome sequences of the cultivated oat[16]. Numerous intergenomic translocations complicate A-genome progenitor identification for the cultivated oat[8,12,16]. The C-genome origin of cultivated oat has been under intense scientific scrutiny. We sample the majority of Avena species (Supplementary Table S130) and present a phylogenetic analysis with divergence time estimates based on nuclear and plastid sequences (Table S231). The objectives are to elucidate infrageneric phylogenetic relationships within Avena, clarify A-, C-, and D-genome evolutionary history for the cultivated oat, and provide a hypothesis for the early diversification history of Avena in the circum-Mediterranean region. (A-PPI in red, A’C-PPI in green, and A’C-PPIII in light green) and two nodes

Methods

Results

Conclusion