title: Multilevel Assessment of Seagrass Response to Thermal Stress: Stress Memory and Epigenetic Changes
Creators: name: Nguyen, Hung Manh
Publisher: name: The Open University
Year: 2022

description: Seagrasses are being threatened globally due to human-induced environmental changes with ocean warming being one of the main players. A better understanding of the interaction between seagrasses and warming is, therefore, crucial to secure a sustainable future for these paramount foundation species. <br><br> Through a literature review and a series of <i>ad hoc</i> mesocosm and field experiments using four seagrass species from the northern (i.e. Mediterranean: <i>Posidonia oceanica, Cymodocea nodosa</i>) and southern (i.e. Australia: <i>Posidonia australis</i> and <i>Zostera muelleri</i>) hemisphere and by applying multi- and inter-disciplinary approaches [i.e. photo-physiology, growth, pigments, gene expression (RT-qPCR and RNA-seq), and genome screening (ddRADseq)], here I (<i><b>i</b></i>) identify potential commonalities in the effects of warming and the responses of seagrasses across different levels ranging from molecular to planetary [e.g. warming strongly affects seagrasses at all levels while seagrass responses diverge amongst species, populations and over depths]; (<i><b>ii</b></i>) demonstrate the existence of thermal stress memory for the first time in seagrasses [e.g. non-primed plants suffered significant reduction in photosynthetic capacity, leaf growth and pigments content, while heat-primed plants were able to cope better with recurrent stressful events]; (<i><b>iii</b></i>) reveal the molecular mechanisms that potentially govern the formation (priming phase) and activation (memory phase) of thermal stress memory in seagrasses [e.g. response to warming of non-primed plants required the involvement of several cellular compartments and processes while in heat-primed plants the response focused on a more limited group of processes]; (<i><b>iv</b></i>) explore the involvement of epigenetic modifications (DNA methylation and histone modifications in particular) in thermal stress response and thermal stress memory in seagrasses [e.g. results from gene expression analyses demonstrated a high activation of genes related to epigenetic modifications and thermal stress memory during the triggering event in both heat-primed and non-primed plants]; (<i><b>v</b></i>) broaden our knowledge in interspecific divergences in response to warming among seagrass species (northern versus southern hemisphere seagrasses and climax versus pioneer species) [e.g. results showed that northern hemisphere <i>Posidonia</i> better dealt with warming than its southern hemisphere counterpart and, in both hemispheres, pioneer seagrasses were more thermal tolerant than climax ones]; (<i><b>vi</b></i>) investigate the molecular basis of local adaptation to high temperature condition in seagrasses [e.g. ddRADseq data analysis identified several outlier loci potentially responsible for thermal stress response and epigenetics]; and finally (<i><b>vii</b></i>) suggest future directions for seagrass research [e.g. studies involving additional species and populations, investigation of the seagrass holobiont, seagrasses as a solution to mitigate climate change among others]. <br><br> This thesis provides novel insights into the field of seagrass ecology and yields potential implications for future seagrass conservation and restoration activities in an era of ocean warming.