Duvall, Melvin R.
M.S. (Master of Science)
Department of Biological Sciences
Climate change has been considered a key driver for adaptations in water usage efficiency (WUE) in plants. Perceptions persist that C4 photosynthesis is indicative of some level of WUE. Here, we examined the interaction and evolution of WUE within the grass family, Poaceae, as it pertains to photosynthetic pathway. Unique to this study is the magnitude of taxa sampled, presence of intrageneric sampling, and use of complete plastid genomes (plastomes) for phylogenomic analyses.
310 species were sampled, including 26 with newly sequenced plastomes, which were assembled de novo from next-generation sequencing data. Additional plastomes were downloaded from the National Center for Biotechnology Information (https://www.ncbi.nlm.nih.gov/), thereby increasing taxonomic and molecular sampling. Critical leaf water potentials were available in the literature for 88 taxa; key classifiers for the remaining taxa were obtained from the literature to infer WUE.
Phylogenetic analyses of complete plastomes were conducted with maximum likelihood (ML) and Bayesian inference methods. Character state transitions were determined using Mesquite software, and analyzed to determine the relationship between photosynthetic pathway and WUE using Pagel’s Correlation Method.
The ancestral condition of Poaceae was determined to be drought intolerant + C3. There was no correlation between C4 photosynthesis and increased WUE within C4 lineages. Analyses across Poaceae indicated that both variables (WUE and photosynthetic pathway) were significantly correlated, but WUE did not depend on photosynthetic pathway and vice versa. We found 66 occurrences of WUE state transitions and state reversals accounted for >70%; transitions became increasingly prevalent towards the branch tips.
Our analyses indicated that C4 photosynthesis, however correlative, is not a driver of increased WUE, but an attribute that likely arose as a result of tertiary evolutionary pressure(s). Multiple state transitions in WUE among lineages also suggests a degree of WUE plasticity.
Nissenbaum, Matthew P., "Dispelling The Mirage of C4-Driven Drought tolerance in Poaceae: A Phylogenomic Study" (2020). Graduate Research Theses & Dissertations. 7497.
Northern Illinois University
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