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Elucidation of Boron Tolerance Mechanisms in Puccinellia Distans (jacp.) Parl. Using a Transcriptomic Approach
(Izmir Institute of Technology, 2017) Öztürk, Saniye Elvan; Frary, Anne
The amount of boron in soil is important for agronomic plants. As an abiotic stress condition, boron toxicity causes significant decreases in crop yields. Puccinellia distans (Jacq.) Parl. (P. distans), common alkali grass, is found throughout the world and can survive in soils with boron concentrations that are lethal for other plant species. Indeed, P. distans accumulates very high levels of this element. Despite these interesting features, very little research has been performed to elucidate the boron tolerance mechanism in this species. In this study, P. distans samples were analyzed by RNA sequencing to identify genes and miRNAs related to boron tolerance and hyperaccumulation. The results indicated that the hyperaccumulation mechanism of P. distans involves many transcriptomic changes including: alterations in the malate pathway, changes in cell wall components that may allow sequestration of excess boron without toxic effects, and increased expression of at least one putative boron transporter and two putative aquaporins. MiRNAs are also altered under stress conditions. The presence of miRNAs as stress regulator elements is an example of post-transcriptional regulation of stress related mechanisms. Additionally these small RNAs could affect their target genes by positive or negative regulation. Therefore, changes not only in miRNAs but also in their targets are important to understand their roles in hyperaccumulation. For example, downregulation of miRNA under stress could cause target accumulation. These mechanisms could be key in plant adaptation to new conditions. Elucidation of the boron accumulation mechanism is important in developing approaches for bioremediation of boron contaminated soils.
Elucidation of Boron Stress Signaling Pathways in Yeast
(Izmir Institute of Technology, 2015) Uluışık, İrem; Koç, Ahmet
Boron is an essential micronutrient not only for plants but also for many other organisms. The excess of boron causes toxicity and the mechanism of this toxicity is not known. The yeast Saccharomyces cerevisiae was used as a model system in this study. In order to reveal boron metabolism related genes, a genome-wide screen has been conducted. Among the identified mutants, six boron resistant and eight boron sensitive mutants were chosen for further investigation to understand how cells cope with boron stress. Boron resistant mutants were found to have increased levels of boron efflux pump ATR1 and its transcription activator Gcn4. The sensitive mutants were lacking the genes that are involved in different cellular pathways. They were found to accumulate higher amounts of boron inside the cells upon boron treatment. To reveal how boron stress is conducted to Gcn4 transcription factor, the deletion mutants of transcription factors that are known to regulate GCN4 were investigated in terms of their effects on Gcn4 and ATR1 expression. Additionally, signaling cascades that converge on Gcn4 transcription factor such as TOR, PKA, and SNF1 pathways were analyzed for their roles in boron stress response mechanism. We found that the Gcn system is activated by the uncharged tRNA stress in response to boron treatment and that GCN1, which plays a role in transferring uncharged tRNAs to Gcn2, was necessary for the kinase activity of Gcn2. Additionally, boron treatment caused the phosphorylation of eIF2α in mammalian cells, in a similar manner to that of yeast cells, which suggested that boron toxicity and tolerance mechanisms were conserved between yeast and mammals.

Phd Degree / Doktora

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