Evaluating transcriptomic and metabolomic adaptations to heat stress in brassica napus (oilseed rape)

Abstract

Oilseed rape (Brassica napus) is an essential oilseed crop, accounting for approximately 12% of the world’s vegetable oil production. Its ability to adapt to various climates, has made it one of the predominant oil crops in Europe. Previous research on Brassica species has shown a negative relationship between heat stress and seed yield and quality. To date, only few studies have addressed the impact of heat stress on the transcriptome and metabolome of B. napus especially during the flowering stage and the underlying cellular mechanisms are still poorly understood. To address this, combining genetic studies with different omics approaches will provide the means to explore the intricate responses arising following exposure to heat stress and accomplish a system-level understanding of how heat stress alters growth and metabolism of oilseed rape. This thesis presents (i) a comprehensive review of the impact of heat stress on the physiology and genetics of B. napus with a focus on the reproductive stages, along with the mechanisms involved in heat stress response. (ii) A heat treatment experiment simulating a heatwave during the flowering stage of B. napus, which caused a significant transcriptional and metabolic changes in buds and leaves, including the down-regulation of many respiratory pathways. RNA-seq analysis showed that heat stress resulted in the differential expression of many genes involved in key biological processes such as heat shock, regulation of cellular processes, transcription factors, cell wall remodelling, sugars and secondary metabolites transport and metabolism. At the metabolomic level, heat stress increased the content of carbohydrates (glucose, fructose and sucrose) and aliphatic glucosinolates (gluconapin, progoitrin) in the leaves but decreased the content of the indolic glucosinolate (glucobrassicin). Additionally, heat treatment also reduced yield and altered oil composition. (iii) This thesis also presents a Cytoscape plugin to visualise genes-TFs interactions in a user-friendly environment. Using the plugin, the top DEGs identified in the heat treatment experiment were found to interact with a wide range of TFs, with members of the MYB, NAC, and WRKY families showing the highest number of gene interactions. Overall, these results revealed important components of heat stress response and tolerance mechanisms in B. napus. The identified genes and metabolites could form the theoretical basis for potential biotechnological applications and a genetic resource for further studies towards the identification and development of high-yield and nutritious varieties that can cope with the heat predicted by the global climate change.