title: Evidence for adaptive evolution of low-temperature stress response genes in a Pooideae grass ancestor.
abstract: Adaptation to temperate environments is common in the grass subfamily Pooideae, suggesting an ancestral origin of cold climate adaptation. Here, we investigated substitution rates of genes involved in low-temperature-induced (LTI) stress responses to test the hypothesis that adaptive molecular evolution of LTI pathway genes was important for Pooideae evolution. Substitution rates and signatures of positive selection were analyzed using 4330 gene trees including three warm climate-adapted species (maize (Zea mays), sorghum (Sorghum bicolor), and rice (Oryza sativa)) and five temperate Pooideae species (Brachypodium distachyon, wheat (Triticum aestivum), barley (Hordeum vulgare), Lolium perenne and Festuca pratensis). Nonsynonymous substitution rate differences between Pooideae and warm habitat-adapted species were elevated in LTI trees compared with all trees. Furthermore, signatures of positive selection were significantly stronger in LTI trees after the rice and Pooideae split but before the Brachypodium divergence (P < 0.05). Genome-wide heterogeneity in substitution rates was also observed, reflecting divergent genome evolution processes within these grasses. Our results provide evidence for a link between adaptation to cold habitats and adaptive evolution of LTI stress responses in early Pooideae evolution and shed light on a poorly understood chapter in the evolutionary history of some of the world's most important temperate crops.
authors.affiliation: Department of Medical Genetics, Oslo University Hospital and University of Oslo, Oslo, Norway.
authors.forename: Magnus D
authors.initials: MD
authors.lastname: Vigeland
authors.affiliation: Helmholtz Zentrum München, Institute of Bioinformatics and Systems Biology, Ingolstädter Landstrasse 1, München, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Spannagl
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, DK-4200, Slagelse, Denmark.
authors.forename: Torben
authors.initials: T
authors.lastname: Asp
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, DK-4200, Slagelse, Denmark.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Paina
authors.affiliation: Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, NO-1432, Ås, Norway.
authors.forename: Heidi
authors.initials: H
authors.lastname: Rudi
authors.affiliation: Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, NO-1432, Ås, Norway.
authors.forename: Odd-Arne
authors.initials: OA
authors.lastname: Rognli
authors.affiliation: Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, NO-1432, Ås, Norway.
authors.forename: Siri
authors.initials: S
authors.lastname: Fjellheim
authors.affiliation: Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, NO-1432, Ås, Norway.
authors.forename: Simen R
authors.initials: SR
authors.lastname: Sandve
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D002980:Climate; D003080:Cold Temperature; D019143:Evolution, Molecular; D017343:Genes, Plant / Q000235:genetics*; D012275:Oryza / Q000235:genetics; D010802:Phylogeny; D006109:Poaceae / Q000235:genetics*; D012641:Selection, Genetic; D016415:Sequence Alignment; D045868:Sorghum / Q000235:genetics; D013045:Species Specificity; D013312:Stress, Physiological / Q000235:genetics*; D003313:Zea mays / Q000235:genetics
keywords: Pooideae; adaptive evolution; climate adaptation; cold; habitat shift; temperate grasses