Eragrostis nindensis: unravelling senescence in an African desiccation tolerant grass

Food security is one of the most important global challenges facing the world today, especially in the context of climate change. Research has been conducted into a unique group of plants, called “resurrection plants”, that can withstand up to 95% tissue water-loss without compromising viability by, inter alia, undergoing extensive metabolic reprogramming and suppressing senescence. In this thesis the African desiccation tolerant grass Eragrostis nindensis (Fical & Hiern) was used as a model plant to identify which biological processes are unique to senescence and critical for desiccation tolerance. When desiccated, the older leaves of E. nindensis senesce, whereas, the younger leaves recover fully upon rehydration, thereby displaying two phenotypes in a single species. Comparing these two tissue types can show how senescence upon abiotic stress is regulated. Differences in transcript abundances between the two tissue types during drying and rehydration was analysed through RNA-seq analysis, coupled with physiological quantitative traits, mass spectrometry analyses and immunoblotting. The transcriptome reflected a transcriptomic reprogramming towards desiccation tolerance by maintaining transcription of genes that control desiccation tolerance traits in both tissue types, however, only the desiccation tolerant (non-senescent) tissue appeared to suppress senescence and maintained translational control. It was hypothesised that the non-senescent tissues regulate and stabilise RNA. The older tissues were unable to suppress senescence, which resulted in cell death. Lipids accumulated in the non-senescent tissue, particularly unsaturated triacylglycerols. It was proposed that lipid droplets that accumulated during drying were stabilised through, in part, the protein expression of oleosin. These lipid droplets appeared to provide a mechanical stabilisation and energy-providing role in the non-senescent tissue. The transcription of genes that control desiccation tolerance traits was generally maintained in both tissue types, however, translation was prevented in the senescent tissue. The non-senescent tissue therefore appeared to engage in a regulation of senescence at the translational level, rather than a fine-tuned transcriptional regulation. The aim of this work was to provide a critical baseline for future studies working on E. nindensis, and desiccation tolerance and senescence in resurrection plants in general. Ultimately, understanding water-deficit stress in the context of senescence can help to improve drought resistance in crops to ensure food security, particularly in Africa.

Grantor

Department of Molecular and Cell Biology

Year dc:date.issued

2019

Author dc:creator

• Madden, Christine Frances

Advisors dc:contributor.advisor

• Farrant, Jill Margaret
• Mundree, Sagadevan G

• Molecular and Cell Biology

Handle dc:identifier.uri

https://hdl.handle.net/11427/31652

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/31652