NMR-based metabolomics of transgenic and non-transgenic sweet orange reveals different responses in primary metabolism during citrus canker development

Introduction Citrus canker, a disease caused by Xanthomonas axonopodis pv. citri (Xac) bacteria, has been responsible for extensive economic losses in citriculture. In this work, we report the metabolic responses of citrus plants during disease development. This information can be useful for understanding the natural mechanism of plant defense beyond helping design new varieties and/or genetically modified genotypes for tolerance/resistance against citrus canker. Objectives To understand how primary metabolism is affected in two sweet orange genotypes during citrus canker development. Methods H-1 NMR spectroscopy together with chemometrics was used to evaluate the metabolic changes caused by Xac infection at various time points (days 4, 12 and 20) in Citrus sinensis L. Osbeck leaves from non-transgenic and transgenic plants expressing the antibacterial peptide sarcotoxin. Results The results revealed a high level of metabolic similarity between the studied genotypes without Xac infection. However, after Xac infection, the plants responded differently to disease development. The non-transgenic genotype showed altered early precursors of some secondary metabolites (tryptophan, tyrosine and putrescine) in addition to signaling metabolites of biotic stress (putrescine and dimethylamine), and the drastic reduction of gluconeogenesis was the overall metabolic cost for defense. The transgenic genotype suffered late metabolic changes due to the protective stoichiometric role of sarcotoxin. In addition, the oxidative stress response was more balanced in transgenic than in non-transgenic plants. Conclusion An NMR-based metabolomic approach was useful for understanding plant-pathogen interactions in citrus canker. Our findings provide valuable preliminary insights into different stages of citrus canker development.