QUANTIFYING GENETIC EXPRESSION OF DEFENSE RESPONSE HORMONES IN SELENIUM HYPER-ACCUMULATOR SPECIES STANLEYA: A NOVEL INTER-SPECIFIC APPROACH
Michael Adair1, Jennifer Cappa2, Jiameng Wang2, Mark Simmons2, Elizabeth Pilon-Smits2.
1Oklahoma State University, Stillwater, OK, 2Colorado State University, Fort Collins, CO.
The quantified differences in gene expression within the species S. pinnata and S. elata may lead to discovery of the levels of gene regulation needed for Se hyperaccumulation in Stanleya, thereby advancing phytoremediation, agriculture, and medicine. Variances in gene expression were statistically quantified within the biological pathways for salicylic acid, jasmonic acid, and ethylene, which are active in stress response to selenium (Se) in the genus Stanleya (Brassicaceae). Transcription rates from three bioreplicates of two Stanleya species (hyperaccumulator S. pinnata and non-accumulator S. elata), consisting of individual plant samples with specified growing conditions of +Se and -Se, were compared for hormone biosynthesis processes, transcription factors, and stress response. Sequences were aligned and confirmed following a flow of bioinformatic tools: TAIR, MAFFT, BLASTn, and Mesquite. Up and down regulation was segregated and quantified in Microsoft Excel where a t-test of the averaged bioreps was performed to quantify expression rate between species and treatments. Flow charts were created to designate positions of enzymes in hormone synthesis and show their expression differences. We found several genes producing significantly different (p = < 0.05) expression rates between S. pinnata and S. elata while other sequences were similarly expressed or completely absent in one transcriptome or the other. Expression variances ranged widely. ICS2, a salicylic acid biosynthesis enzyme, expressed at 162 RPKM (reads per kilobase per million) in S. pinnata root +Se vs. 9.3 RPKM in S. elata root +Se (P = 1.92 x 10-6) while transcription factor MYB29 displayed little variance under the same conditions at 6.19 RPKM vs. 8.46 RPKM respectively (P = 0.005).