Ecology and evolution of cold tolerance in Panicum hallii




Palacio Mejía, Juan Diego

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Given that plants are sessile organism, they are continuously challenged by both biotic and abiotic stresses in natural and agricultural conditions which they are forced to acclimate or adapt. One of the major abiotic stressors affecting plant growth and development, and thereby limiting distribution of plants and crop production, is low temperature. It is estimated that crop yield is affected by cold stress in 57% of the global land area. To study the ecology and evolution of cold tolerance in plants, Hall's panicgrass (Panicum hallii), a perennial C₄ grass native to North America, was used to investigate cold tolerance due to its adaptation to diverse environments across its natural distribution. Three approaches were followed in this study: 1. The genetic diversity and population structure as well the response to cold stress were evaluated in samples collected across the natural distributions of the species. 2. Then, genomic regions associated to response to cold temperatures were found by QTL analysis of a RIL population. 3. Finally, a global transcriptome analysis was conducted in a set of selected phenotypes to identify candidate genes involved in cold responses. For the population genetic approach, we evaluated the genomic and morphological diversity as well as the genetic structure of the C₄ grass Panicum hallii using ddRAD molecular approaches. We found strong genetic and morphological divergence between varieties and strong genetic structure between the seven populations that was strongly correlated with geological and ecological conditions. Following the genetic diversity analyses, we utilized QTL and global gene expression approaches to determine the early chilling stress transcriptome response of P. hallii. This analysis revealed 16 genes occurring within a major QTL interval and exhibiting expression responses. Six genes were previously associated with responses to cold stress in studies with other plant species, and five genes were identified with unknown functions. Accordingly, the results here not only aid in the discovery of the genetic mechanism that underline local adaptation but also provide a foundation to improve switchgrass yield under cold conditions



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