Combining genetics and metabolomics to understand abiotic stress tolerance in plants

© 2013 Dr. Camilla HillAustralia is affected by both drought, because of its geographic location, high temperatures and variable rainfall patterns, and salinity, because of increased irrigation and defoliation of arable lands. This results in significant losses of agricultural production, estimated to be upwards of 50%. The aim of my PhD project is to combine genetics and genomics resources together with metabolomics to create a broader picture of how plants tolerate different abiotic stresses, particularly drought and salinity stress. Chapter 1 is a literature review that gives an overview of the current understanding of plant responses to drought and salinity, genetics and QTL analysis, and plant metabolomics. It also briefly discusses the main instrument technologies and data analysis methods used in this study. Chapter 2 describes the investigation of metabolite responses to salt stress of different Arabidopsis thaliana genotypes with altered expression of the sodium transporter, AtHKT1;1. A broad range of metabolites and mineral ions in shoots and roots of different AtHKT1;1 genotypes and its parental strains were measured before and after salinity stress. This study revealed a reciprocal relationship of metabolite differences between the AtHKT1;1 knockout line and the AtHKT1;1 overexpressing lines. Using correlation analysis, associations between the sodium ion content and several sugars were identified, suggesting that regulation of sugar metabolism is a major metabolic site that is important in plant responses to salinity stress. Chapters 3 and 4 describe the utilization of metabolomics and genomics to define metabolite quantitative trait loci (QTL) that will facilitate the identification of drought tolerant genes as well as breeding tools in the future. This study was conducted on a doubled haploid (DH) population from a cross between drought intolerant (Kukri) and tolerant (Excalibur) wheat cultivars, grown in the field in South Australia in 2006 under severe drought. Metabolite profiling of the complete DH population was carried out using non-targeted gas chromatography-mass spectrometry (GC-MS, Chapter 3) andliquid chromatography-mass spectrometry (LC-MS, Chapter 4) analyses to identify and quantify both known and unknown metabolites. Genetic linkage maps and marker scores allowed defining the genetic loci controlling metabolite traits, including novel metabolites, onto the wheat genome. These were related to QTL identified through the analysis of plant growth and yield traits under drought. The final Chapter 5 describes the relationship between the genetic and metabolic information and the association of such results with previous published literature and suggests future directions of further studies