Environmentally-Induced Variation in Gene Expression and rDNA Copy Number among Flax Genotrophs

Marshall Lukacs

Abstract


Flax (Linum usitatissimum) undergoes a variety of genomic rearrangements in response to environmental stresses such as those caused by nutrient imbalance or heat. Of particular interest in flax is Linum Insertion Sequence-1 (LIS-1), a 5.7 Kb sequence of DNA that is inserted into a conserved target sequence in some varieties of flax while growing under stress. Pl, L, and S are all closely related with Pl being the progenitor line that changes in response to environmental stress, and L and S being stable genotrophs derived from Pl. Only S contains LIS-1. Using BLAST and the complete genome sequence of the oil flax variety Bethune, 79 potential genes surrounding the LIS-1 insertion site were identified. PCR primers were developed for 64 of these genes. In addition, 9 primers were developed from potential miRNA sequences that may be important in the generation or function of LIS-1. Using RTPCR, the relative expression levels of the 64 genes and 9 miRNA genes in the three genotrophs were determined and the data will be verified with Northern blotting. Significant expression differences in genotroph S could be the result of expression regulation, by the presence of LIS-1, as an adaptation to stress. The functions of genes displaying large expression differences include but are not limited to: drought resistance, bicarbonate transport, glucose-6-P transport, mitochondria formation and ATPase activity. The second piece of this research concerns the responsiveness of flax crosses. The most effective manner of testing for stress response in flax varieties is scanning for the presence of the LIS-1 insertion during growth under inducing conditions. Nonresponsive varieties (Motley and Bethune) were crossed with the responsive Stormont Cirrus variety (Pl) to determine the heritability of LIS-1 formation. The crosses display the expected simple Mendelian genetics ratios for a trait with dominant and recessive alleles. However, the observed segregation pattern makes it unlikely that the LIS-1 insertion event is mediated by one gene, suggesting that multiple loci are involved that display dominance. Further research is required to map the location and determine the function of these Quantitative Trait Loci (QTLs) for LIS-1 induction.

Keywords


Gene Expression, Flax, Rearrangements

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