Evolution of temperature-mediated flowering in grasses

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In temperate regions, global warming is already causing shortened winters that are interrupted by extreme weather events, such as unseasonably warm temperatures. Although warmer temperatures can often stimulate rapid growth, the fact that many temperate plants use low temperatures as a cue to prepare for flowering makes it difficult to predict the consequences of warming on their reproductive yield. Luckily, studies of plant adaptations to past climate change can be informative for predicting what will happen in the future. This proposal aims to dissect the evolutionary history of flowering responses to high and low temperatures in the economically important grass family, and to determine the genes underlying these responses. Outcomes of the project will be a better understanding of how and why temperature extremes affect flowering in grass species adapted to different climates, and the discovery of novel flowering time genes that can be targeted in crop breeding. The integration of teaching and research, centered around temperature-regulated flowering in grasses, will also provide rich opportunities to the next generation of scientists charged with solving some of the world’s most pressing problems.In many temperate crops, including the Pooideae grasses wheat and barley, the attainment of floral competency occurs in response to extended periods of above freezing cold (vernalization), thus allowing rapid flowering with the onset of spring. Available evidence suggests a single origin of vernalization responsiveness in the ancestor of the ~3,800 species containing Pooideae, with at least one independent origin in the other large PACMAD grass clade. The flowering pathway of both groups appears to relay the cold signal through the epigenetic modification of genes within the FRUITFULL (FUL) clade of transcription factors, whereby time-dependent modifications to chromatin result in a ‘memory’ of winter. In some non-vernalization responsive cultivars of wheat, FUL transcription can also be triggered by high temperatures, whereas in vernalization responsive cultivars high temperatures cause devernalization and delayed flowering. What is not well understood is if and how the ancestral grass integrated temperature cues into its flowering pathway, whether independent origins of vernalization and devernalization evolved through the recruitment of similar genes and regulatory elements, and what the history of temperature-regulated flowering evolution means for adaptability of grasses to future weather events that are predicted to become increasingly erratic and extreme. To address these questions, this project will combine growth experiments, spatiotemporal comparative transcriptomics, and CRISPR-based functional analyses to provide insight into adaptive constraints caused by cross-talk between the low and high temperature pathways in distinct grass lineages, and to isolate novel temperature-regulated flowering time genes and regulatory regions that can potentially be used for cereal improvement.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.