Eutrema salsugineum is an extremophile plant that is naturally tolerant to abiotic stresses such as high salinity, drought and cold (Inan et al., 2004, Griffith et al., 2007; MacLeod et al., 2015). It is emerging as a stress tolerant model plant, due to its short life cycle and high genetic similarity to the model plant Arabidopsis (Inan et al., 2004). There are two well-studied ecotypes of Eutrema, the Shandong ecotype from the Shandong Province of China, and the Yukon ecotype that grows in the Yukon, Canada. Principal component analysis (PCA) comparing the transcriptomes of three Yukon cabinet plants, three Shandong cabinet plants, and three Yukon field plants revealed that Yukon cabinet plants load negatively along PC3, while the Shandong cabinet and Yukon field plants load positively. Of the top 50 genes that contribute to this negative loading, 12 are related to sulfur deficiency, leading to the hypothesis that the cabinet plants are deficient for sulfur. To test this hypothesis cabinet potting soil was supplemented with calcium sulfate dihydrate to raise the sulfur level to approximately that of Yukon field soil. Sulfur-treated plants were compared to those grown on unsupplemented soil and untreated plants had significantly reduced biomass and leaf area. Additionally, RT-qPCR showed that relative to sulfur-supplemented plants, untreated plants had 4 to 177-fold higher transcript levels of two sulfur deficiency marker genes, Sulfur deficiency induced 1 and γ-glutamylcyclotransferase 2;1. While these findings are consistent with untreated plants experiencing a sulfur deficiency, there was no difference in chlorophyll content, and rosette sulfur levels were only 1.1-fold higher in the sulfur-treated plants. The third most negatively loading gene on PC3 was identified as XLOC_003912, a long non-coding RNA of unknown function that is only expressed in Yukon cabinet plants. Because it shows a similar loading pattern to the 12 sulfur nutrition-related genes, it was hypothesized to be involved in sulfur homeostasis. RT-qPCR showed that XLOC_003912 expression was lower in sulfur-treated compared to untreated plants. A method was developed to suppress XLOC_003912 expression in Yukon Eutrema plants by Virus Induced Gene Silencing (VIGS). In addition to providing insight into the function of XLOC_003912, this technique can be used in future studies for determining the role of novel genes in Eutrema salsugineum. / Thesis / Master of Science (MSc) / Eutrema salsugineum is a model for studies of plant abiotic stress tolerance. I determined that the Yukon ecotype of Eutrema displays elevated expression of sulfur deficiency genes when grown in cabinets. Increasing soil sulfur level roughly 10-fold in the potting mix led to significantly increased biomass, leaf area and leaf number and reduced transcript abundance of sulfur deficiency genes. One sulfur-responsive gene encodes a novel long non-coding RNA. I adapted a method for transiently repressing its expression, an approach that can be used to explore the function of this and other novel genes in Eutrema.

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