The role of transposable elements in the regulation of stress response gene expression

Q Wu1,2, S Eichten3, K Kazan2, CY Zhou1 and MB Wang2

  1. Southwest University, Chongqin, PR, 400716
  2. CSIRO Agriculture, Clunies Ross Street, ACT, 2601
  3. Australian National University, Canberra, ACT, 0200

We have recently discovered that a group of stress response genes are positively regulated by DNA demethylases in Arabidopsis. These genes are enriched for transposable element (TE) sequences in promoters, show inducible expression upon Fusarium oxysporum infection, and are repressed in DNA demethylase mutants where the TE sequences are differentially methylated. These observations suggest that TEs in the promoter are required for the regulation of the stress response genes, and that DNA demethylases function to minimize DNA methylation at the TEs to maintain their regulatory activity. The aim of this project is to understand how these promoter TEs regulate the expression of the stress response genes. Two approaches have been employed. First, selected TE-containing promoters are transcriptionally fused with the β-glucuronidase (GUS) sequence and these promoter:GUS constructs are transformed into wild-type and DNA demethylase mutant Arabidopsis, followed by gene expression and DNA methylation analysis under normal and F. oxysporum infection conditions to determine if TEs are the key regulatory element. Second, promoter sequences and expression levels of these stress response genes are compared among Arabidopsis ecotypes using both bioinformatics and wet-lab approaches to identify ecotypes that show variation in promoter TE. This is then followed by comparing the expression difference under normal and F. oxysporum infection conditions. Analysis of the transgenic promoter:GUS plants has confirmed that the TE-containing promoter fragments contain all the required information for endogenous gene expression patterns. Furthermore, methylation analysis of one transgenic promoter so far has shown that the promoter TE region is hypermethylated in the DNA demethylase mutant, which is associated with repressed GUS expression. Ecotype comparison to date has identified Arabidopsis ecotypes with expression difference associated with potential promoter TE differences. Further analysis is continuing for both the GUS plants and the ecotypes, and data will be presented.