Abstract
Despite the scientific and economic importance of maize, little is known about its specialized metabolism. Here, five maize organs were profiled using different reversed-phase liquid chromatography-mass spectrometry methods. The resulting spectral metadata, combined with candidate substrate-product pair (CSPP) networks, allowed the structural characterization of 427 of the 5,420 profiled compounds, including phenylpropanoids, flavonoids, benzoxazinoids, and auxin-related compounds, among others. Only 75 of the 427 compounds were already described in maize. Analysis of the CSPP networks showed that phenylpropanoids are present in all organs, whereas other metabolic classes are rather organ-enriched. Frequently occurring CSPP mass differences often corresponded with glycosyl- and acyltransferase reactions. The interplay of glycosylations and acylations yields a wide variety of mixed glycosides, bearing substructures corresponding to the different biochemical classes. For example, in the tassel, many phenylpropanoid and flavonoid-bearing glycosides also contain auxin-derived moieties. The characterized compounds and mass differences are an important step forward in metabolic pathway discovery and systems biology research. The spectral metadata of the 5,420 compounds is publicly available (DynLib spectral database, https://bioit3.irc.ugent.be/dynlib/).
Highlights
IntroductionThe metabolome, i.e., the complete set of metabolites in an organism, provides a phenotypic read-out, which can yield insight into how genes, transcripts, proteins and metabolites drive and influence the phenotype of a system
This limitation was confirmed by our observation that only 0.93% up to 2.46% of the unique collision-induced dissociation (CID) spectra of the maize specialized metabolome could be annotated through matching with publicly available spectral databases
The inclusion of all DynLib subDBs, and different types of CID spectra, for spectral matching led to more annotations than could be obtained for any of the individual subDBs
Summary
The metabolome, i.e., the complete set of metabolites in an organism, provides a phenotypic read-out, which can yield insight into how genes, transcripts, proteins and metabolites drive and influence the phenotype of a system This property makes metabolomics an essential player in the understanding of cellular systems and in decoding the function of genes [13]. Metabolome data and knowledge of metabolite identities remain scarce for maize, especially concerning its specialized (secondary) metabolism. This information gap prevents understanding the system-wide biology of maize, and the continuous development of maize as a model system
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