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 Some transposed sequences enter nonessential regions of the genome allowing regions of genes to survive

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

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

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

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

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

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

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

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

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

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

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