Molecular mechanisms contributing to local adaptation to drought in tropic and temperate populations of two Eucalyptus species

Abstract

In this thesis I investigate the molecular mechanisms that underpin drought stress, recovery and memory response of eucalypts. I used an experimental approach with water availability manipulated under controlled growth conditions to quantify physiological and transcriptomic (RNA-seq) responses in tropic and temperate populations of Eucalyptus tereticornis and Eucalyptus grandis. I grew the plants in greenhouses simulating tropic (28.5oC) and temperate (18oC) temperatures. The plants were kept well-watered for 86 days, then had a dry treatment for 7 days, followed by a rewatering treatment for 7 days. Physiological measurements (including photosynthesis and stomatal conductance) and leaf collection for RNA analysis were taken at the end of the treatment period. RNA-seq data was collected through the Illumina protocol providing millions of 100bp pair-end reads, which were mapped onto the Eucalyptus grandis annotated genome (Myburg et al., 2014), I conducted a population and GEI response analysis. In the former analysis, I looked at the differential gene expression within each population among stress, recovery, and memory. In GEI or Genotype by Environment Interaction vii analysis, I directly looked at the differences between tropic and temperate populations in each species. I then proceed to look at the Gene Ontology or GO terms these differentially regulated genes enriched. I aimed to find molecular patterns of local adaptation and hypothesised: a) stress and recovery will have more differential responses in all populations and species, b) temperate populations will exhibit stronger responses than tropic populations, c) Local adaptation patterns will be stronger in the wet habitat species and d) gene functions contributing to the response to “Abiotic stimulus”(GO:0009628) and “Stress”(GO:0006950) will be overrepresented in response to drought. In conclusion, my study found both differential regulation patterns among populations (G; adaptation) and differential gene regulation in each population in response to treatments (E; plasticity). Furthermore, I found that local adaptation (GEI) is more enhanced in ‘dry species’ than in ‘wet species’. My study highlights the complex nature of drought responses in ecologically important species, as well as highlight candidate genes for future research.

Date of Thesis submission	2022
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Paul Rymer (Supervisor) & Collin Ahrens (Supervisor)