Drought tolerance and its evolution in conifers including UK commercial species

Thesis

This work seeks to contribute to our understanding of conifer tree responses to drought. Research in this field has historically privileged the study of the changing anatomy, physiology, and metabolism of trees under adverse environmental conditions. The main reason for this lies in the size and complexity of conifer genomes, which posed limitations to genetic studies in this important plant group. Recently, fast-evolving sequencing technologies have unlocked conifer “mega-genomes” and made a considerable number of genetic resources available for researchers. Here, we investigate the genetic mechanisms governing the responses to soil water deficit of diverse conifer species, that are relevant to the UK forestry market but are faced with human-made climate change. We explored how dynamic expression of key genes involved in abscisic acid (ABA) biosynthesis and catabolism may relate to the isohydry paradigm. Several frameworks have been proposed, that include a range of traits and definitions to explain diverging water regulation responses falling along the isohydric spectrum. We developed new evidence for the role of selected candidate genes, in particular 9-cis-epoxycarotenoid dioxygenases (NCEDs), based on their expression in conifer species with contrasting responses. These may be the master regulators of contrasting ABA accumulation profiles in conifer foliage. We also characterised genes encoding putative NCEDs in detail, comparing three key conifer species and model angiosperms, through in silico analyses, and produced a recombinant protein from P. sitchensis (PsNCED1) to enable functional characterisation in vitro. We found a high degree of 1D-3D sequence conservation, indicating that conifers may have evolved a rate limiting step for ABA biosynthesis. This information forms a basis for new gene functional studies on conifers, which is important in the context of newly developing forest management programs. Finally, we studied P. sitchensis and its natural hybrid with P. glauca, P. lutzii. P. sitchensis is widely exploited in the UK timber market and represents a large portion of planted forests. We selected an array of cultivars, including hybrids, and tested their phenotypic variability in relation to drought stress. Although similarly conservative, cultivars deployed variable drought responses that differed in their use of water. Exploring drought adaptability by use of hybrids is one approach for developing resilient forests, which will be of interest to tree breeders looking for alternative planting materials. We believe that this work will contribute to bridge the gap between phenotypic and genomic studies in conifers and will help establish better breeding practices.

Authors: Rizzuto, G

• DOI: 10.5287/ora-ppxrz8aj0
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: forestry; gene expression; conifer; abscisic acid; isohydry; drought
• Subjects: Molecular genetics; Forest biodiversity; Ecology