Understanding salinity tolerance mechanisms in finger millet through metabolomics

Finger millet (Eleusine coracana Gaertn L.) is an underutilized but nutritionally rich climate resilient food crop that is generally cultivated on marginal lands. Soil salinization is a major abiotic stress that leads to a reduction in growth and yield by affecting various physiological and metabolic processes in plants. The existence of genotypic variation for salt tolerance in finger millet indicates the possibility of crop improvement via plant breeding. The overall objective of the study was to identify metabolic changes associated with improved salt tolerance in finger millet. Understanding tolerance mechanisms plays a pivotal role in the development of elite cultivars. Based on the consensus of several phenotypic data at the germination and seedling stages, we further evaluated two accessions (IE 518 and IE 405) with morphophysiological parameters and metabolomics to dissect the salinity tolerance mechanisms in finger millet. Significant phenotypic separation of IE 518 and IE 405 for salt tolerance was reflected through differences in several physiological processes such as maximum quantum yield of photosystem II (F_V/F_M), net photosynthesis rate (P_n), shoot Na⁺ ion accumulation, and oxidative stresses (electrolyte leakage and malondialdehyde content). However, both accessions showed retention of K⁺ ions, which underscores the role of ion homeostasis in finger millet. Pathway enrichment analysis with the uniquely salt regulated metabolites identified key metabolic pathways such as stress signaling, biotin metabolism, energy metabolism, amino acid biosynthesis, and sugar metabolism in IE 518. An enhanced accumulation of reducing sugars (mannose and melibiose) and amino acids (L-Proline and GABA) in IE 518 under salinity suggests maintaining osmotic balance as a key tolerance mechanism in finger millet.