Thesis Type: Doctorate
Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Biology, Turkey
Approval Date: 2015
Student: FERHUNDE AYSİN
Supervisor: AYŞE ELİF ERSON BENSANAbstract:
Environmental stress with climate change currently contributes to approximately 50% of crop loss occurring world-wide. Thellungiella halophila is a plant that is native to highly saline and semiarid environments and exhibits an exceptional ability to tolerate abiotic stress. Primarily, the determination of relatively high GSH/GSSG ratios (glutathione assay), elevated proline accumulation, less MDA (lipid peroxidation) production and increased anthocyanin levels and less reduced RWC of the T. halophila (Shandong and Yukon ecotypes) after exposure to increasing concentrations of NaCl allowed us to support that Thellungiella tolerate environmental stress conditions. Genomic studies have shown that differences in stress tolerance arise not only from the presence or absence of stress-associated genes but also from their regulation. In plants, miRNAs are the key gene regulators that have been shown to control various developmental processes and responses to environmental stresses. In order to assess the expression profiles of miRNAs in abiotic stress tolerance of T. halophila ecotypes, salt, cold and drought treatments were carried out. As a result, we identified the changes in the expression profiles of seven conserved miRNAs under 250 mM NaCl, 4°C and 200 mM mannitol using Northern-Blot analysis and TaqMan qRT-PCR assays. Four of the stress related miRNAs (miR156, miR169, miR319 and miR393) were found to be downregulated and three (miR159, miR398 and miR169) were found to be upregulated during exposure to salt, cold and drought stress. Based on the conservation of mature miRNA sequences, potential target genes for miRNAs were also predicted by using conservation of miRNA target sites among species. The target mRNA expression analysis were done by RT-qPCR after exposure to salt stress. RT-qPCR results showed decrease in the expression of miR156, miR169, miR319 and miR393 with a corresponding upregulation of their putative target mRNA transcripts (SPL10, NF-YA5, ITD1 and WRKY33, respectively). In addition, the induction of miR159 was accompanied by the down regulation of its probable target mRNA (HEC1). Taken together, these findings suggest that a number of conserved miRNAs may function in Thellungiella halophila ecotypes tolerance to environmental stresses.