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What are Transposons?

What are Transposons?. “ Selfish DNA ” Interspersed repeats “ move ” in the genome. Bacterial Insertion Sequences. Transpositions inactivate essential genes, killing the host and the IS element it carries

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What are Transposons?

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  1. What are Transposons? • “Selfish DNA” • Interspersed repeats • “move” in the genome

  2. Bacterial Insertion Sequences • Transpositions inactivate essential genes, killing the host and the IS element it carries • Some transposed sequences enter nonessential regions of the genome allowing regions of genes to survive

  3. Transposase • Required for transposition of IS element to new site • Target site direct repeat sequence are immediately adjacent to both ends of the inserted elements

  4. Transposase Functions 3’ of Is element to 5’ ends of cut donor DNA

  5. McClintock’s Discovery • Spontaneous mutations in maize affect production of enzymes required for pigment

  6. 2 Movable Elements 1. Activator elements Encodes mRNA for transposase protein. -recognizes the terminal repeats and catalyzes transposition to a new DNA site 2. Dissociation elements -deletion mutant of Activator that has lost the necessary sequences to move on its own

  7. Results of Transposons • Can result in an increase in the number of a transposon if it occurs during S phase of cell cycle • after a DNA transposon leaves a gene, the resulting gap will probably not be repaired correctly • Transposition in germ cells to their new sites is passed on to succeeding generations

  8. Phytophthora infestans • Oomycete – aka “water mold” – fungus-like eukaryotic organism “pseudofungus” • Cause of potato blight, which brought about the Irish Potato Famine

  9. Genome organization • Transposon-poor regions • Genes needed for survival • Transposon-rich regions • Genes used for pathogenesis • 74% of genome is transposon-rich • Most transposons in genome are inactive

  10. Plant Immune System • Pathogen-associated Molecular Patterns (PAMPs) causes response of PAMP-triggered Immunity (PTI) • Pathogens produce effectors to suppress PTI • Plants produce R proteins to suppress effectors • High selective pressure on effector genes leads to rapid evolution

  11. RNA Silencing • P. infestans uses sRNA to restrict the activity of transposons

  12. Effector Silencing • Proximity to transposons leads to silencing of effector genes • Caused by formation of heterochromatin at and around transposons • Heterochromatin spreads ~300 to 600 bases from transposon

  13. 563 RXLR effectors • 35 within 300bp of transposons • 106 within 600bp • 283 within 2kb

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