Statistical measures for validating plant genotype similarity assessments following multivariate analysis of metabolome fingerprint data

Abstract

Metabolome fingerprinting offers opportunities for ‘first pass’ evaluation of compositional similarity between plant genotypes. Compositional “substantial equivalence” testing is a popular concept in the literature in relation to food safety; however reported studies do not provide a systematic and standard approach to quantify similarity in a high dimensional data context. We have undertaken a large scale screen of Arabidopsis genotypes for evidence that individual genetic modifications effect plant phenotype at the level of the metabolome. From this study we propose pragmatic alternative measures that could in the future be used to assess substantial equivalence in GM foods under realistic data paucity constraints and without prior feature selection. Evaluation of classifier accuracy in supervised data mining approaches by bootstrap error estimation provided a robust tool for model validation. Receiver operating characteristics (such as AUC) provide an alternative measure of predictive ability by displaying the relationship between sensitivity and specificity. Additional specific measures based on scatter matrices and sample margins have also been investigated. We illustrate the application of such metrics on a large metabolic profiling data set derived from analysis of 27 genetically distinct Arabidopsis thaliana mutants. We show that agreement exists between model margins, eigenvalue, accuracies and AUC characteristics produced by three different classifiers (Random Forest, Support Vector Machine and Linear Discriminant Analysis). Comparisons between mutants with no observable phenotypic differences to the parent ecotype provided a baseline for model significance metrics; whilst comparison of mutants with increasingly distinct phenotypic alterations generated predictable changes in these measures of similarity.