Prolonged heat stress in Brassica napus during flowering negatively impacts yield and alters glucosinolate and sugars metabolism

Mariam Kourani ¹ Maria Anastasiadi ¹ John Hammond ² Fady Mohareb ^1*

• ¹ The Bioinformatics Group, Centre for Soil, Agrifood and Biosciences, Cranfield University, Bedford, United Kingdom
• ² School of Agriculture, Policy and Development, University of Reading, Reading, England, United Kingdom

Oilseed rape (Brassica napus), one of the most important sources of vegetable oil worldwide, is adversely impacted by heat wave-induced temperature stress especially during its yield determining reproductive stages. However, the underlying molecular and biochemical mechanisms are still poorly understood.In this study, we investigated the transcriptomic and metabolomic responses to heat stress in B. napus plants exposed to a gradual increase of temperature reaching 30 °C in the day and 24 °C at night for a period of 6 days. High Performance Liquid Chromatography (HPLC) and Liquid Chromatography-Mass Spectrometry (LC-MS) was used to quantify the content of carbohydrates and glucosinolates respectively. Results showed that heat stress reduced yield and altered oil composition. Heat stress also increased the content of carbohydrate (Glucose, Fructose and Sucrose) and aliphatic glucosinolates (Gluconapin, Progoitrin) in the leaves but decreased the content of the indolic glucosinolate (Glucobrassicin). RNA-Seq analysis of flower buds showed a total of 1892, 3253, 4553 differentially expressed genes at 0, 1 & 2 DAT (Days after Treatment) and 4165 and 1713 at 1 & 7 DOR (Days of Recovery) respectively. Heat treatment resulted in down regulation of genes involved in respiratory metabolism namely Glycolysis, Pentose Phosphate Pathway, Citrate Cycle and Oxidative Phosphorylation especially after 48 hrs of heat stress. Other down regulated genes mapped to sugars transporters, nitrogen transport and storage, cell wall modification and methylation. In contrast, up regulated genes mapped to small heat shock proteins (sHSP20) and other heat shock factors that play important roles in thermotolerance. Furthermore, two genes were chosen from the pathways involved in the heat stress response to further examine their expression using real time RT-qPCR. The global transcriptome profiling, integrated with the metabolic analysis shed the light on key genes and metabolic pathways impacted and responded to abiotic stresses exhibited as a result to exposure to heat waves during flowering. DEGs and metabolites identified through this study could serve as important biomarkers for breeding programs to select cultivars with stronger resistance to heat. In particular, these biomarkers can form targets for various crop breeding and improvement techniques such as marker assisted selection.