Ancient Duplication and Lineage-Specific Transposition Determine Evolutionary Trajectory of ERF Subfamily across Angiosperms.

AP2/ERF transcription factor family plays an important role in plant development and stress responses. Previous studies have shed light on the evolutionary trajectory of the AP2 and DREB subfamilies. However, knowledge about the evolutionary history of the ERF subfamily in angiosperms still remains limited. In this study, we performed a comprehensive analysis of the ERF subfamily from 107 representative angiosperm species by combining phylogenomic and synteny network approaches. We observed that the expansion of the ERF subfamily was driven not only by whole-genome duplication (WGD) but also by tandem duplication (TD) and transposition duplication events. We also found multiple transposition events in Poaceae, Brassicaceae, Poales, Brassicales, and Commelinids. These events may have had notable impacts on copy number variation and subsequent functional divergence of the ERF subfamily. Moreover, we observed a number of ancient tandem duplications occurred in the ERF subfamily across angiosperms, e.g., in Subgroup IX, IXb originated from ancient tandem duplication events within IXa. These findings together provide novel insights into the evolution of this important transcription factor family.

Genome size variation and polyploidy prevalence in the genus Eragrostis are associated with the global dispersal in arid area.

Background: Biologists have long debated the drivers of the genome size evolution and variation ever since Darwin. Assumptions for the adaptive or maladaptive consequences of the associations between genome sizes and environmental factors have been proposed, but the significance of these hypotheses remains controversial. Eragrostis is a large genus in the grass family and is often used as crop or forage during the dry seasons. The wide range and complex ploidy levels make Eragrostis an excellent model for investigating how the genome size variation and evolution is associated with environmental factors and how these changes can ben interpreted. Methods: We reconstructed the Eragrostis phylogeny and estimated genome sizes through flow cytometric analyses. Phylogenetic comparative analyses were performed to explore how genome size variation and evolution is related to their climatic niches and geographical ranges. The genome size evolution and environmental factors were examined using different models to study the phylogenetic signal, mode and tempo throughout evolutionary history. Results: Our results support the monophyly of Eragrostis. The genome sizes in Eragrostis ranged from ~0.66 pg to ~3.80 pg. We found that a moderate phylogenetic conservatism existed in terms of the genome sizes but was absent from environmental factors. In addition, phylogeny-based associations revealed close correlations between genome sizes and precipitation-related variables, indicating that the genome size variation mainly caused by polyploidization may have evolved as an adaptation to various environments in the genus Eragrostis. Conclusion: This is the first study to take a global perspective on the genome size variation and evolution in the genus Eragrostis. Our results suggest that the adaptation and conservatism are manifested in the genome size variation, allowing the arid species of Eragrostis to spread the xeric area throughout the world.

SMRT sequencing of the Oryza rufipogon genome reveals the genomic basis of rice adaptation.

Asian cultivated rice is believed to have been domesticated from a wild progenitor, Oryza rufipogon, offering promising sources of alleles for world rice improvement. Here we first present a high-quality chromosome-scale genome of the typical O. rufipogon. Comparative genomic analyses of O. sativa and its two wild progenitors, O. nivara and O. rufipogon, identified many dispensable genes functionally enriched in the reproductive process. We detected millions of genomic variants, of which large-effect mutations could affect agronomically relevant traits. We demonstrate how lineage-specific expansion of gene families may have contributed to the formation of reproduction isolation. We document thousands of genes with signatures of positive selection that are mainly involved in the reproduction and response to biotic- and abiotic stresses. We show that selection pressures may serve as forces to govern substantial genomic alterations that form the genetic basis of rapid evolution of mating and reproductive systems under diverse habitats.