Methylation of PP2A in Arabidopsis – Stress tolerance and gene expression analysis
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PP2A is a highly conserved enzyme complex in eukaryotes that is involved in various signal transduction pathways including hormone-regulated pathways in plants. This enzyme is composed of catalytic C, scaffolding A, and regulatory B subunit. The PP2A activity is regulated by methylation of terminal amino acid leucine in the catalytic subunit C. Leucine carboxyl methyl transferase 1 (LCMT1) is an enzyme that methylates PP2A by using S-adenosyl-L-methionine (SAM) as methyl donor. The lcmt1 mutant, where the LCMT1 enzyme is knocked out possesses unmethylated PP2A-C. This mutant still grows almost as WT under standard growth conditions, yet with some phenotypic differences such as more elongated leaves and earlier flowering than WT. However, as this regulatory mechanism, e.g., methylation of PP2A, is conserved from yeast to mammals and different species of plants, it is believed to be crucial for plant survival under certain types of stresses. We here investigated the importance of PP2A methylation in Arabidopsis thaliana under competitive conditions and evaluated certain genes that strongly influenced by the methylation status of PP2A-C. The oxidative stress devastatingly stunted the growth of lcmt1, whereas the root lengths of the mutant were more significantly affected than WT under high salt stress. The differences between WT and lcmt1 regarding the morphological responses toward nutrient deficiency or toxicity were striking. The root lengths of the mutant were remarkably inhibited under sulfur deficiency and sulfur toxicity, whereas withdrawal of three important nutrients such as Mg, S and Cl crucially impaired both shoot weight and root length of the mutant compared to WT Arabidopsis. Our analysis of several genes involved in the Fe assimilation pathway and sulfur uptake pointed out some fascinating facts related to the defensive capability of the mutant under stress. We noticed a comparatively lower expression of Sulfate transporter 1;2 (SULTR1;2) and Sulphur deficiency induced 1 (SDI1) genes in lcmt1, when compared with WT upon sulfur depletion, which indicated less sulfur uptake by the mutant. Furthermore, Fe superoxide dismutase 1 (FSD1) was up-regulated and Protein phosphatase 2A subunit A2 (PP2AA2) was down-regulated in the lcmt1 mutant during sulfur depletion, hence showed higher ROS production and weaker PP2A-A2 subunit, respectively, when compared to WT.
Master's thesis in Biological chemistry