Metabolomics in Plant Pathogen Defense: From Single Molecules to Large-Scale Analysis.

Plants produce a high diversity of secondary metabolites that are involved in a wide range of different functions, including stress tolerance, signaling molecules for interactions with other species (allelopathy), and protecting plants against herbivores and pathogens. With the rise of more accessible, high-throughput mass spectrometry and new analytical tools, it becomes feasible to identify and validate new secondary metabolites involved in pathogen resistance or assign new roles to previously detected compounds. In this review, we provide a brief overview of the major pathogen defense-associated classes of secondary metabolites, with a focus on those with direct anti-pathogen function. For each class, we highlight one or more typical examples representing the class to give a comprehensive summary of some of the work done to date. In the second part of this review, we highlight how new technological advances and high-throughput experiments in combination with other sources of -omics data, such as genomics and transcriptomics, can accelerate the studies on secondary metabolites and help to link these compounds to genotypes. Employing such approaches will improve our understanding of chemical defenses against plant pathogens and allow for rapid development of markers for resistance breeding.