Molecular physiological responses and acclimation of the seagrass species Z. muelleri to light limitation

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Understanding how a keystone marine species responds to its extrinsic environment is important to ensure adequate conservation measures are in place, especially with increasing reports of climate change and anthropogenic disturbance events. For the Southern Hemisphere seagrass, Zostera muelleri, this scenario is no different. This keystone species is native to Australia and New Zealand, providing many socio-economic benefits to the coastal zone. Over the past few decades, a reduction in water quality (light limitation) has led to numerous reports of Z. muelleri meadow loss in Australia and New Zealand. Although seagrass biologists have a firm understanding of the physiological, morphological and ecological changes within light limited Z. muelleri meadows, no current knowledge exists on how Z. muelleri responds to light limitation at the transcriptional level. By investigating transcriptional regulation, new knowledge was obtained on how this species responds to light limitation, allowing for more appropriate conservation measures. Encompassing the advances in RNA-Seq, this project has examined how Z. muelleri responds to light limitation over a 14-day period, through transcriptional regulation, photobiology and physiology, both at the nuclear and chloroplastic level. Main findings indicate that important regulational shifts occur in genes associated with photosynthesis, photo-pigments, carbon metabolism, reactive oxygen species (ROS) homeostasis and secondary defence metabolism. Both nuclear and chloroplast encoded genes involved in photosynthetic processes have been shown to be correlated with downstream changes in photophysiology, and thus are both crucial for the response as well as the acclimation to light limitation. This research also compared genome-guided transcriptome assembly versus de novo assembly, indicating the superiority of genome-guided protocols when a genome is available. Whilst this PhD thesis offers a new level of knowledge to seagrass biologists, it also provides candidate molecular markers, which can be used in future monitoring efforts and population genetic studies.
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