Decoding the metabolic landscape of maize responses to experimentally controlled drought stress: A greenhouse case study

Metabolomics, a multidisciplinary omics science, has disruptively positioned itself as one of the key pillars in systems biology, decoding metabolic circuits that govern biological processes in a specific environment. This chapter illustrates the use of metabolomics in investigating plant-environment interactions; describing a greenhouse case study on maize plants responding to drought conditions. In this study, stress-responsive metabolic adjustments, spanning various pathways in maize primary and secondary metabolisms, were profiled. Alterations in hydroxycinnamic acid (HCA) metabolites, such as chlorogenic acids, HCA-amides, HCA-hydroxycitric acids, and HCA-sugars, were observed. The levels of chlorogenic acids, (particularly feruloylquinic-, caffeoylquinic-, and coumaroylquinic acids) decreased as a response to drought conditions. Furthermore, maize responses to drought conditions involved differential changes in amino acid levels (methionine, proline, tyrosine, and valine), in malic-, isocitric- and fumaric acids, and in oxylipins. The elucidated maize stress-responsive metabolic landscape reflects a reprograming of metabolism toward physiological and cellular processes such as stomatal regulation, ROS scavenging and redox homeostasis, regulation of intracellular ionic content, cell wall remodeling, and nutrient assimilation. Elucidating these abiotic-related metabolomic alterations is a piece of the puzzle of the complex regulation of cellular defensome to adverse environmental factors such as water-deficit. Furthermore, through this case study, the chapter articulates vital elements within workflows and approaches employed in an environmental metabolomics study, presenting methodological principles, and experimental and epistemological considerations that are followed to derive biologically meaningful information.