Dynamics of host glutathione and glutathione related enzymes in Macrophomina phaseolina-sorghum bicolor interaction

Glutathione and its related enzymes play an integral role in cellular detoxification processes and redox buffering. A genome wide transcriptome profiling was conducted through RNA sequencing to investigate the dynamics of glutathione and related enzymes in sorghum bicolor (L.) Moench in response to Macrophomina phaseolina (MP) infection. Compared to mock inoculated control treatment, MP significantly upregulated the glutathione synthetase, glutamate cysteine ligase (involved in glutathione biosynthesis), glutathione s-transferase (GST), glutathione peroxidase (GPX), and glutathione reductase (GR) genes in a charcoal rot susceptible sorghum genotype (Tx7000), but not in a resistant genotype (SC599) at 7 days post- inoculation. The net log2 fold up-regulation of the aforesaid genes in MP-inoculated Tx7000 was 1.9, 0.9, 120.0, 9.0, and 4.5, respectively. To confirm the gene expression data, cell extracts were acquired from MP- and mock-inoculated resistant (SC599, SC35) and susceptible (Tx7000, BTx3042) sorghum genotypes and their reduced (GSH), oxidized (GSSG) glutathione, GST, GPX, and GR activities were measured using standard protocols. A significantly reduced GSH/GSSG ratio was observed in Tx7000 and BTx3042 indicating the strong oxidative stress experienced by charcoal rot susceptible genotypes under MP infection. MP significantly increased the GST, GPX, and GR activities of Tx7000 and BTx3042. Although augmented GR activity contributes to cellular GSH restoration, the enhanced GST activity leads to diminishing GSH pools through vacuolar sequestration of GSH-S-conjugates. This eases the oxidative stress confronted by susceptible genotypes under MP infection and in turn contributes to reduced charcoal rot susceptibility. The importance of GSH in controlling the MP infection associated oxidative stress was further supported by the significantly reduced disease severity observed in Tx7000 and BTx3042 upon exogenous GSH application.