Transcriptome-wide identification of genes involved in Ascorbate–Glutathione cycle (Halliwell–Asada pathway) and related pathway for elucidating its role in antioxidative potential in finger millet (Eleusine coracana (L.))

Finger millet is being recognized as a potential future crop due to their nutrient contents and antioxidative properties, which are much higher compared to the other minor millets for providing health benefits. The synthesis of these nutritional components is governed by the expression of several gene(s). Therefore, it is necessary to characterize these genes for understanding the molecular mechanisms behind de novo synthesis of nutrient components. Apart from this, these important compounds could also serve as candidate genes for imparting stress tolerance in other crop plants also. In the present study, effort has been made to identify genes involved in Ascorbate–Glutathione cycle (Halliwell–Asada Pathway) and related pathway genes for elucidating its role in antioxidative potential mechanism through transcriptome data analysis. APX, DHAR, MDHAR, GR, and SOD have been identified as the key genes of the pathway in two genotypes GP-1 (low Ca2+) and GP-45 (high Ca2+) of finger millet with reference to rice as a model system, besides, 30 putatively expressed genes/proteins were also investigated. Furthermore, the sequences of identified genes were analyzed systematically; gene ontology (GO) annotation and enrichment analysis of assembled unitranscripts were also performed using Blast2GO. As a result, 49 GO terms, 5 Enzyme Commission (EC) numbers, and 2 KEGG pathway maps were generated. GO results revealed that these genes are mainly involved in two biological processes (BP), viz., oxidation–reduction process (GO:0055114) and cellular oxidant detoxification (GO:0098869), and showed oxidoreductase activity (GO:0016491). KEGG analysis showed that APX, DHAR, MDHAR, and GR are directly connected to biosynthetic pathways of secondary metabolites, mainly polyphenolic compounds (flavonoid, tannin, and lignin) involved in glutathione metabolism (KEGG:00480) and ascorbate and aldarate metabolism (KEGG:00053). While SOD, is indirectly connected and also has significant medicinal attributes and antioxidant properties. Moreover, Fragments Per Kilobase of transcript per Million mapped reads (FPKM) values were also calculated for expression analysis and found that the FPKM values of genes present in GP-1 are higher than that of GP-45. Thus, GP-1 genotype was found to have higher stress regulated gene expression in comparison to GP-45. Taken together, the present transcriptome-based investigation unlocks new avenues for systematic functional analysis of novel ROS scavenging candidate genes that could be effectively applied for improvising human health and nutrition.