Browsing by Author "Czajka, Karolina M."

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Effects of nickel toxicity on seed germination and expression of genes associated with nickel resistance in Populus tremuloides
(2018-04-30) Czajka, Karolina M.
Although Nickel is an essential nutrient for plant growth in low concentrations, its excessive amounts in soil above threshold values can result in toxicity. The main objectives of the present research were to determine the effects of different doses of nickel on a) trembling aspen (Populus tremuloides) seed germination and b) gene expression. This study revealed that nickel in agarose media even at a low dose inhibits seed germination. In soil however, only the highest dose of 1, 600 mg of Ni per 1 kg of soil has detrimental effects on germination of P. tremuloides seeds. P. tremuloides seedlings were resistant to 150 mg /kg, 400 mg /kg, and 800 mg /kg of Ni doses in growth chamber screening tests. At high Ni dose of 1, 600 mg /kg, differential responses were observed as Ni- resistant, moderately resistant, and susceptible genotypes were identified. Expression of the AT2G16800 gene was repressed with increasing nickel concentration and this effect was most significant at the 800 mg/kg Ni dose. Surprisingly, the study also revealed that the higher concentration of potassium nitrate without nickel (800 mg/kg and 1, 600 mg/kg) induced a significant upregulation of the NAS3 and NRAMP4 genes.
Transcriptome and methylome analysis of trembling aspen (Populus tremuloides) under nickel stress.
(2022-04-28) Czajka, Karolina M.
Nickel is an essential micronutrient required at low concentrations for adequate plant growth and health. However, excessive amounts of bioavailable nickel ions in the surrounding soil can result in plant toxicity symptoms. Plants have evolved heavy metal tolerance mechanisms to adapt and cope with this abiotic stressor. The main objectives of the present research were to 1) further characterize the P. tremuloides transcriptome 2) compare gene expression dynamics between nickel-resistant and nickel-susceptible P. tremuloides genotypes with Whole Transcriptome (WT) sequencing, 3) determine the effects of different nickel concentrations on P. tremuloides gene expression and, 4) assess global methylation levels in P. tremuloides under nickel stress. Trembling aspen (Populus tremuloides) seedlings treated with varying concentrations of nickel nitrates (150 mg Ni / 1 kg of dry soil, 800 mg / kg, and 1, 600 mg / kg) showed phenotypic segregation of physical toxicity symptoms at the highest nickel dose of 1, 600 mg / kg. This study revealed that a metal transport protein (Potrs038704g29436 – ATOX1-related copper transport) was among the top upregulated genes in resistant genotypes when compared to susceptible plants. Other upregulated genes associated with abiotic stress were identified including a Dirigent Protein 10, GATA transcription factor, Zinc finger protein, Auxin response factor, Bidirectional sugar transporter, and thiamine thiazole synthase. Overall, an upregulation in ribosomal and translation activities was identified as the main response to Ni toxicity in the resistant plants. The results of the dosage analysis suggested that the 800 mg / kg nickel dose is the threshold at which an early abiotic stress response may be triggered as seen by the highly upregulated LEA protein and two calcium binding proteins when compared to water. The cluster of genes that had increased gene expression with increasing nickel dose also had multiple enriched GO terms related to heavy metal and abiotic stress including metal ion transport, antioxidant activity, photosynthesis, and ribosomal activity. Lastly, the initial screen for potential global methylation differences between nickel-resistant genotypes and water showed no significant difference in overall methylation levels. However, the potassium nitrate control for the 1,600 mg / kg dose did show significantl hypomethylation in comparison to the nickel-treated or water control samples. Future experiments could use targetspecific methylation and gene expression assays to investigate the biological significance of the heavy metal stress candidate genes identified in this top-down study in trembling aspen. Understanding the heavy metal tolerance mechanisms and responses used by hardy species like trembling aspen is important for environment bioremediation and maintenance of healthy ecosystems.