Metabolomics study on Arabidopsis thaliana abiotic stress responses for priming, recovery, and stress combinations

Abstract

Temperature, water, and light are three stress factors that have major influences on plant growth, development, and reproduction. Plants can be primed to an acclimated state by a prior mild stress to enhance their resistance to future stress. ‘Priming’ is related to plant stress ‘memory’ during recovery. Plants may need to balance between keeping the memory for enhanced stress defense and resetting for maximum growth and development during recovery. In the field, plants are more often to encounter a combination of different abiotic stresses rather than a specific single stress condition. Plant responses to a combination of stresses may exhibit quite unique defense and acclimation responses as compared to the response elicited by each individual stress, which should not be simply considered as the sum of the two different stresses. However, the simultaneous occurrence of multiple stress events is rarely studied experimentally, especially by metabolomics methods. Metabolomics, the comprehensive, quantitative and qualitative analysis of small molecules, is an emerging 'omics' platform that is an important next-generation systems biology approach. By providing an instantaneous “snapshot” of metabolic processes that occur in an organism, metabolomics can potentially provide insightful molecular mechanism information to questions about physiological function in complex biological systems. The objective of this thesis research was to use both untargeted and targeted metabolomics approaches to investigate plant shared and unique metabolic features in responses to single as well as multiple abiotic stresses, the priming effect of temperature stresses, plant memory during recovery phase, and the relationships between combined stress with each of individual stresses. An ultra-high pressure liquid chromatography-high resolution mass spectrometry (UHPLC-HR-MS)-based metabolomics approach was utilized. In chapter two, a metabolomics study on Arabidopsis thaliana 11-day-old seedling’s abiotic stress responses including heat (basal and acquired), cold (basal and acquired), drought and high light with 2-day-recovery was performed using a standardized reference system. In chapter three, Arabidopsis thaliana 11-day-old seedlings that were induced by the combination of different abiotic stresses including heat, cold, drought, salinity, and high light, that mimics field environment was studied. From this thesis research, a number of potential stress signatures determined from the untargeted analysis were identified, quantified and clustered by stress response patterns. Central metabolism were found to undergo a complex regulatory process in response to stress. Shared and unique metabolic signatures were identified across different abiotic single and combined stresses. The majority of stress signatures clustered together and exhibited shared response patterns. However, cysteine, glutathione, and maltose showed unique and dramatic patterns, demonstrating large changes in glutathione biosynthesis, glutathione oxidation, and starch degradation. The results showed that only two combined stresses, including high light x cold and cold x salinity, had metabolic effects that reflected both of their constituent single stresses. Most combined stresses had one dominant stress that had a defining impact on the plant metabolic profile. Drought stress is the dominant stress for all of its stress combinations. Two combined stresses, including high light x heat and high light x salinity, showed unique metabolic stress response patterns that are not similar to any of their individual stresses. Most of these metabolic features were specifically changed only in the combined stress, which should thus be considered as novel stress conditions. In summary, this work utilized metabolomics to study plant priming effects, recovery processes, and combined stress responses. It led to an improved understanding of how plants respond to abiotic stresses and may support subsequent studies on plant abiotic stress metabolic flux analyses.