PhD Defence: Shuai Tong
Title: The resilience journey of rice: Root traits, genome editing and silicon-mediated strategies for enhanced abiotic stress tolerance in rice
Supervisor: Professor Ole Pedersen
Assessment committee:
Dean Jacobsen, Department of Biology, University of Copenhagen (Chair)
Dennis Konnerup, Department of Food Science, Århus University, Denmark
Eric J.W. Visser, Department of Experimental Plant Ecology, Radboud University, the Netherlands
Abstract:
Rice holds profound importance for global food security, serving as the primary staple for approximately half of the global population. Notably, it surpasses all other crops by meeting nearly 80% of human food calorie requirements. However, rice production faces challenges due to climate change, with torrential rains leading to flooding followed by droughts. Moreover, vast agricultural areas are affected by salinity, resulting from poor irrigation management and natural disasters. As a result, this thesis was designed to enhance our understanding of root traits in rice that confer tolerance to abiotic stress, with a primary focus on soil flooding and salinity, but with relevance to drought as well.
Firstly, several species of wild rice relatives were cultivated alongside popular cultivars and landraces in drained conditions (simulated in aerated nutrient solution) and in flooded conditions (simulated in stagnant, deoxygenated nutrient solution). The findings indicated that the wild relatives did not possess root traits conferring tolerance to soil flooding beyond what modern Oryza sativa cultivars already exhibited. In contrast, some of the dryland species demonstrated limited phenotypic plasticity in the key root traits under analysis.
The second phase analyzed the potential for de novo domestication of Oryza longistaminata since this wild rice species possesses two important traits of high agricultural value: rhizome bearing and perennial growth. O. longistaminata has already served as a donor for several vital traits that have been introgressed into cultivated rice. However, de novo domestication involves a completely different approach, relying on the complex and quantitative traits already present in the wild relative. Modern genomic tools, such as CRISPR-Cas9, can then be used to subsequently eliminate agronomically undesirable traits like seed shattering, lodging, and poor seed quality. The study concluded that O. longistaminata is an excellent candidate for de novo domestication due to its tolerance to both flooding and drought.
In the final phase, the study investigated the importance of silicon (Si) in the development of two key root traits critical for abiotic stress tolerance in rice: cortical aerenchyma and the outer apoplastic barriers. Si application was found to delay the formation of the outer apoplastic barriers and reduce aerenchyma formation. Si application reduced cell wall depositions of lignin and suberin in the outer parts of the root, resulting in imperfect outer apoplastic barriers, as demonstrated by the accumulation of Na and Cl in the xylem sap. The research therefore supports the idea that outer apoplastic barriers in roots and cortical aerenchyma should be key targets for breeding climate-resilient rice with enhanced abiotic stress tolerance.
