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Summary Grasses are fundamental to human survival, providing a large percentage of our calories, fuel, and fodder for livestock, and an enormous global carbon sink. A particularly important part of the grass plant is the grain‐producing inflorescence that develops in response to both internal and external signals that converge at the shoot tip to influence meristem behavior. Abiotic signals that trigger reproductive development vary across the grass family, mostly due to the unique ecological and phylogenetic histories of each clade. The time it takes a grass to flower has implications for its ability to escape harsh environments, while also indirectly affecting abiotic stress tolerance, inflorescence architecture, and grain yield. Here, we synthesize recent insights into the evolution of grass flowering time in response to past climate change, particularly focusing on genetic convergence in underlying traits. We then discuss how and why the rewiring of a shared ancestral flowering pathway affects grass yields, and outline ways in which researchers are using this and other information to breed higher yielding, climate‐proof cereal crops. 

Abstract Vernalization-responsive plants use cold weather, or low temperature, as a cue to monitoring the passing of winter. Winter cereals can remember the extent of coldness they have experienced, even when winter is punctuated by warm days. However, in a seemingly unnatural process called “devernalization,” hot temperatures can erase winter memory. Previous studies in bread wheat (Triticum aestivum) have implicated the MADS-box transcription factor VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT2) in vernalization based on transcriptional behavior and ectopic expression. Here, we characterized 3 BdVRT2 loss-of-function alleles in the temperate model grass Brachypodium distachyon. In addition to extended vernalization requirements, mutants showed delayed flowering relative to wild-type plants when exposed only briefly to warm temperatures after partial vernalization, with flowering being unaffected when vernalization was saturating. Together, these data suggest a role for BdVRT2 in both vernalization and in its reinitiation when interrupted by warm temperatures. In controlled constant conditions, BdVRT2 transcription was not strongly affected by vernalization or devernalization. Yet, by monitoring BdVRT2 expression in seasonally varying and fluctuating conditions in an unheated greenhouse, we observed strong upregulation, suggesting that its transcription is regulated by fluctuating vernalizing–devernalizing conditions. Our data suggest that devernalization by hot temperatures is not a peculiarity of domesticated cereal crops but is the extreme of the reversibility of vernalization by warm temperatures and has broader biological relevance across temperate grasses. 

Abstract Background and AimsPooideae grasses contain some of the world’s most important crop and forage species. Although much work has been conducted on understanding the genetic basis of trait diversification within a few annual Pooideae, comparative studies at the subfamily level are limited by a lack of perennial models outside ‘core’ Pooideae. We argue for development of the perennial non-core genus Melica as an additional model for Pooideae, and provide foundational data regarding the group’s biogeography and history of character evolution. MethodsSupplementing available ITS and ndhF sequence data, we built a preliminary Bayesian-based Melica phylogeny, and used it to understand how the genus has diversified in relation to geography, climate and trait variation surveyed from various floras. We also determine biomass accumulation under controlled conditions for Melica species collected across different latitudes and compare inflorescence development across two taxa for which whole genome data are forthcoming. Key ResultsOur phylogenetic analyses reveal three strongly supported geographically structured Melica clades that are distinct from previously hypothesized subtribes. Despite less geographical affinity between clades, the two sister ‘Ciliata’ and ‘Imperfecta’ clades segregate from the more phylogenetically distant ‘Nutans’ clade in thermal climate variables and precipitation seasonality, with the ‘Imperfecta’ clade showing the highest levels of trait variation. Growth rates across Melica are positively correlated with latitude of origin. Variation in inflorescence morphology appears to be explained largely through differences in secondary branch distance, phyllotaxy and number of spikelets per secondary branch. ConclusionsThe data presented here and in previous studies suggest that Melica possesses many of the necessary features to be developed as an additional model for Pooideae grasses, including a relatively fast generation time, perenniality, and interesting variation in physiology and morphology. The next step will be to generate a genome-based phylogeny and transformation tools for functional analyses. 

Abstract Evidence suggests that anthropogenically-mediated global warming results in accelerated flowering for many plant populations. However, the fact that some plants are late flowering or unaffected by warming, underscores the complex relationship between phase change, temperature, and phylogeny. In this review, we present an emerging picture of how plants sense temperature changes, and then discuss the independent recruitment of ancient flowering pathway genes for the evolution of ambient, low, and high temperature-regulated reproductive development. As well as revealing areas of research required for a better understanding of how past thermal climates have shaped global patterns of plasticity in plant phase change, we consider the implications for these phenological thermal responses in light of climate change. 

Despite most angiosperms being perennial, once-flowering annuals have evolved multiple times independently, making life history traits among the most labile trait syndromes in flowering plants. Much research has focused on discerning the adaptive forces driving the evolution of annual species, and in pinpointing traits that distinguish them from perennials. By contrast, little is known about how ‘annual traits’ evolve, and whether the same traits and genes have evolved in parallel to affect independent origins of the annual syndrome. Here, we review what is known about the distribution of annuals in both phylogenetic and environmental space and assess the evidence for parallel evolution of annuality through similar physiological, developmental, and/or genetic mechanisms. We then use temperate grasses as a case study for modeling the evolution of annuality and suggest future directions for understanding annual-perennial transitions in other groups of plants. Understanding how convergent life history traits evolve can help predict species responses to climate change and allows transfer of knowledge between model and agriculturally important species.