Untargeted Metabolomics Reveals Altered Pathways in Phytoplasma-Infected Sesame Plants

Abstract

Sesamum indicum is an important oilseed crop rich in nutrients and antioxidants, cultivated worldwide owing to its economic value. Sesame fields are often challenged due to a disease caused by Candidatus Phytoplasma, a cell wall-lacking bacteria. Phytoplasma infection results in alteration in the plant’s physiological and metabolic responses. As metabolites are the final products that aid in a plant’s adaptation to several biotic and abiotic stresses, it is necessary to understand these metabolic changes. However, the changes at the metabolite level after Phytoplasma infection in sesame are poorly understood. To investigate the response of sesame plants to Phytoplasma infection, we analyzed the metabolic changes using liquid chromatography-tandem mass spectrometry (LC–MS/MS/MS). Data analysis led to the detection of 162 metabolites, among which 82 were upregulated, while 62 exhibited downregulating trends in the Phytoplasma-infected tissue. The upregulated metabolites include flavonoids, phenolics, lignans, glucosinolates, terpenoids, phytohormones, and some sugars, like trehalose. Phytoplasma infection also resulted in significant chlorophyll breakdown, suggesting impaired chloroplast physiology. We have also validated this LC–MS/MS data by biochemical analysis and analyzing the expression of a few genes behind the biosynthesis of the concerned metabolites using qRT-PCR analysis. The results indicate that plant metabolic networks undergo reprogramming upon Phytoplasma infection. Understanding this altered metabolic pathway may aid in developing a control measure for this disease.