03-08-2013, 04:22 PM
Metabolomic Approaches to Improve Crop Tolerance Against Biotic Stress
ABSTRACT
Metabolomics – simultaneously assessing large numbers of metabolites within a sample is emerging as a powerful post genomic approach which can provide insights into large scale changes in biochemistry during development or imposition of a stress. Plant metabolomic investigations have almost invariably been based on plants which have been grown under carefully regulated conditions. Metabolomic analyses of plantation crop - Camellia sinensis in response to stresses caused by Exobasidium vexans (pathogen) and Helopeltis theavora (pest) as well as cereal - Oryza sativa following biotic stress caused by Magnoporthe grisea have been carried out. Leaf samples were classified according to disease phenotypes; i.e. either healthy or at one of three phenotypic stages of disease progression. Initial screens exploited Fourier Transform Infrared (FT-IR) spectroscopy to derive metabolic fingerprints for each samples. Multivariate statistical approaches based on Principal Component Analysis (PCA) and Discriminant Function Analysis (DFA) were used to interrogate the derived spectra. DFA was able to describe changes in the metabolic fingerprint within each phenotypic class which were linked to responses to biotic stress and not to variation linked to differing plantation sites. To begin to identify actual metabolite change, leaf samples were profiled using Electrospray-Ionisation Mass Spectrometry (ESI-MS). DFA indicated that changes in the concentration of catechins and phenolics were major features of developing tea blister disease. The identity of these metabolites was confirmed by tandem MS using LTQ Ion Trap MS. Targeted assays established that both the diseases ( blister blight of tea and blast of rice) were also linked to a reduction in the defence hormones, salicylic and jasmonic acids. Thus, it may be that altered agricultural practices or germplasm selection approaches should aim to maintain the levels of these defence hormones during pathogenic challenge. Taken together, data from this study has established that metabolomic studies can be undertaken for other crops which aim to increase field resistance to biotic stress. Properly applied therefore, metabolomics stands ready to play an important role in securing plant productivity against the effects of adverse environmental changes.