Inhibition of TOR signalling in lea1 mutant induces apoptosis in Saccharomyces cerevisiae

The target of rapamycin, TOR, maintains cell growth and proliferation under vivid environmental conditions by orchestrating wide array of growth-related process. In addition to environmental conditions, e.g., nutrient and stress, TOR also governs cellular response to varied intracellular cues including perturbed intracellular mRNA levels which may arise due to altered regulation of mRNA processing at splicing or turnover levels. The purpose of this study is to explore the role of TOR signalling in growth of cells with accumulated unprocessed RNA. Growth analysis of lea1∆ (splicing deficient) was carried out under varied conditions leading to nitrogen starvation. The expression of TORC1 and TORC2 marker genes was examined in this delete strain. Sensitivity of the lea1∆ towards oxidative agents was observed. Apoptosis was analyzed in caffeine-treated lea1∆ cells. The hypersensitivity of lea1∆ cells towards caffeine is outcome of highly perturbed TOR signalling. The growth defect is independent of PKC pathway. Cells with accumulated unprocessed RNA experience high oxidative stress that induces apoptosis. An inadequate TOR signalling in lea1∆ cells substantiates the effect of oxidative stress induced by accumulated RNA to the extent of inducing cell death via apoptosis.     

Biochemical Evidence for the Activation of Distinct Subsets of Mitogen-Activated Protein Kinases by Voltage and Defense-Related Stimuli

Activation of mitogen-activated protein (MAP) kinases is a common reaction of plant cells in defense-related signal transduction pathways. To gain insight into the mechanisms that determine specificity in response to a particular stimulus, a biochemical approach has been employed. Photoautotrophic suspension culture cells of tomato (Lycopersicon peruvianum) were used as experimental system to characterize MAP kinase activation by different stress-related stimuli. An elicitor preparation of the tomato-specific pathogen Fusarium oxysporum lycopersici was shown to result in the simultaneous induction of four kinase activities that could be separated by ion-exchange chromatography. The simultaneous activation of multiple MAP kinases was further substantiated by distinct pharmacological and immunological properties: a differential sensitivity toward various protein kinase inhibitors and a differential cross-reaction with isoform-specific MAP kinase antibodies. In contrast to the two fungal elicitors chitosan and the F. oxysporum lycopersici preparation, the plant-derived stimuli polygalacturonic acid and salicylic acid were shown to activate distinctly different subsets of MAP kinases. Application of a voltage pulse was introduced as a transient stress-related stimulus that does not persist in the culture. Voltage application activates a distinct set of MAP kinases, resembling those activated by salicylic acid treatment, and generates a refractory state for the salicylic acid response. The inhibitory effect of nifedipine indicates that current application may directly affect voltage-gated calcium channels, thus, providing a tool to study various calcium-dependent pathways.