The Dynamic Genome

Transposons

Transposable element (transposon)A sequence of DNA that is competent to move from place to place within a genome

Ds Transposition

weedtowonder.org/jumpingGenes.html

Retrotransposon Content (million BP)

Transposon Caught in the Act (Burst)

• Most TEs are inactive molecular “fossils”.

• Active TEs evolved to insert into “safe-havens.”

• Host sequesters Tes and regulates their movement (RNAi-based mechanism).

• TEs can provide advantages. (A means to rapidly reorganize the genome in response to stress.)

How do organisms live with TEs?

MITE (Miniature -Inverted repeat TE)

Deletion-derivative of Ping: requires Ping transposase

Ping/mPing

OVER 1000 mPing copies

Japonica strains

mP

ing

cop

y n

um

ber

Naito et al PNAS (2006))

mPing

Over 1000 copies of mPing in 4 related strains….

Takatoshi Tanisaka lab (Kyoto University)

mPing copy number in O.japonica

Genomic Distribution of mPing

0

2

4

6

8

10

12

5'UTR exon intron 3'UTR

(%)

shared(n=926)

unshared(n=736)

expect.

UTR Exon UTR

Genic Distribution of mPing

Os02g0135500 (-41)

0

0.5

1

1.5

2

2.5

control cold salt dry

NBEG4 (mPing+)A123 (mPing+)A157

mPing Alters Gene Expression

Nipponbare EG4

mPing Confers Salt Tolerance

Naito et al, Nature, 2009

• Massive amplification largely benign• Subtle impact on the expression of many genes• Produces stress-inducible networks (cold, salt, others?)• Generates dominant alleles

Rapid mPing amplification (burst)

Transposons and Zapotec Oral Tradition

Virigina Walbot

• Fields of those who who steal Zapalote Chico maize will be poisened

• Transcription of intact Mutator transposase repressed by homozygous inhibitor

• Outbreeding releases repression• Mutator activation results in • sterility (hybrid dysgenesis)• Analogous to P elements in fruit flies

• (relatively) simple

• incredibly abundant

• evolve rapidly

• promote rapid genome evolution

• largely ignored (discovery)

TEs for Student Research Projects