Evolutionary potential for increased thermal tolerance in a widespread annual plant

The frequency and intensity of extreme heat events is harming natural populations of plants and animals and challenging agricultural production. It is thus in the national interest to understand heat tolerance and to discover ways to protect populations from heat stress. This project examines the ability of plants to tolerate and adapt to extreme heat, focusing on field mustard, a plant species that includes important vegetable and oil crop varieties as well as wild populations spanning a wide range of latitudes. Sampling from across the broad global range of this species, the project aims to discover which populations are most tolerant of heat stress and which genes help to confer this heat tolerance. In addition, the project will mimic natural evolutionary change by exposing a set of plants to brief heat stress at the budding stage, which is particularly sensitive to high temperatures. The plants will then be cross-fertilized, and this process continued for multiple generations. This type of selection is likely to lead to the rapid evolution of increased heat tolerance, allowing the traits and genes involved to be studied. Ultimately, the well-being of people will be improved by the contribution this work will make towards a more resilient food supply. The project will also help train the next generation of students and key results will be incorporated into a number of courses. Canola growers collaborating with this project will use the results to help with crop improvement. In combination, these outcomes will benefit society by providing a better understanding of adaptation to extreme heat, training the STEM workforce, educating society, and securing important food resources for the future. Mechanisms underlying variation in heat tolerance are poorly studied in natural plant populations, limiting the ability of researchers to predict plant responses to environmental change, find strategies for stress mitigation, and protect food security through targeted crop breeding. The proposed project aims to fill this knowledge gap by associating spatiotemporal differences in heat tolerance of an important crop and wild plant species, Brassica rapa, with phenotypic, genetic, epigenetic, transcriptomic, and climatic variation. Several hypotheses will be addressed by combining observations from both natural populations that vary extensively in latitude and climate of origin and test populations experimentally evolved with or without heat stress at the bud stage to promote pollen selection and very rapid evolution. Together, these studies will provide an original assessment of how natural populations have evolved in the past and will potentially evolve in the future in response to heat stress. The proposed experiments will open the door to addressing the evolution of heat tolerance from a genomics, transcriptomics and methylomics perspective, specifically through the lens of adaptive allelic variation, changes in gene expression, and signatures of methylation. More broadly, the results will elucidate the importance of pollen selection for evolutionary rescue during conservation and restoration efforts as well as identify key heat tolerance genetic modules that can be used by plant breeders to develop region-specific, future-proofed canola lines. 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.