Role of transposon elements in evolution in plant

1. Retotransposons and their role in
plant genome evolution
Jatindra Nath Mohanty, JRF

2. Types of Transposable Elements

3. Are Retrotransposon active?
Further the resulted PCR products are subjected to cloning and sequencing or are
directly sequenced
Putative retrotrasposon sequences are compared to preliminary determined plant
LTR retrotrasposon .(Ex-Recently some gypsy–like env retrotransposons such as
Gossypium, H. vulgare and O.sativa).
Evidence for retrotransposition activity have been reported from analysis of
LTR sequences. LTR have been demonstrated for tobacco- Tnt1A and Tto1,
barley- BARE- 1, rice- Tos17 and maize- Huck retrotransposon
Retrotransposon sequences might be amplified by polymerase chain reaction
(PCR) of genomic or cDNA using primer complementary to highly conserved
sequences of LTRs or RT domain of retrotrasposon

4. Retrotransposon in plant
development
• Some Retrotrasposon express in specific tissues
system in plant development.
• Tnt1- expressed in roots.
• Opie,Huck, Cinful retroelements, barley BARE-1
has been observed in leaf tissues
• In maize Prem-2 element has been detected only
in early microspores forming stage.
• But the expression of retrotransposon is control
under some hormone and some dev. factor in
animal and yeast (plant not known clearly as less
knowledge on comparative study)

5. Retrotrasposon & MITE in genome size of
plant

6. Contd…..
The Ty1-copia elements:
• BARE-1 from barley and Opie-1 and Huck2 from maize are
present in 20,000–200,000 copies .
The Ty3-gypsy :
• Cinful-1 is present in 20,000 copies in the genome of maize,
The LINE:
• Del2 is present at 250,000 copies in Lilium
The SINE
• TS is present at 50,000 copies in tobacco .
• Retrotransposons have been found to be present at a high
copy number in centromere in chromosome also.

7. Retrotrasposon as mutagens
I Insertion mutation
• Non-coding sequences can also generate mutations. Their insertion within introns
can result in tissue specific alternative splicing leading to the production of fully
active or truncated proteins in different tissues
Coding strand Non coding strand/intron insertion
1. Bs 1 retro element insert in to
Adh gene in Maize
2. Tnt retro element insert in to
Tobacco nitrate Reductase in in
Tobacco
3. Tos 17 insert in rice plant
1. maize waxy (Wx) gene
2. mPing element in rice
(glume mutant)

8. Retrotrasposon in silencing
mechanisms
Gene silencing
PTGS (mRNA degradation) TGS(promotor inactivation)
• Silencing was first described in transgenic plants, but related
phenomena have now been described in a broad range of normal
organism
• The tobacco Tto1 retrotransposon becomes silent in Arabidopsis.
• Some time mutations affecting different chromatin remodeling
factors reactivate silent mobile elements.
• Very short defective elements related to LTR-retrotransposons,
known as TRIMs have also been described ,which helps in gene
silencing.

9. Stress activation of plant LTR-retrotransposons

10. Contd…….
• In a similar way, Tto1 expression is induced by
wounding and cell culture associated stresses.
• By wounding Tos17 activity is also strongly induced in
cell culture in rice.
• Sharp microclimate changes can modify the copy
number of the BARE-1 retrotransposon in wild barley.
• All these results suggest that both Tnt1 and Tto1 are
activated in defense-associated stresses because their
promoters are similar to that of plant defense genes
and bind the same defense induced transcription
factors like MYB-1, NtMYB2 etc.

11. Impact of Retrotrasposon on the
evolution of genes and genomes
• LTR-retrotransposons and MITEs seems to have been a
major player in plant gene evolution
• The insertion of MITEs within genes can modify the
promoter and terminator sequences, as well as the
translational start and coding sequences .
• And also LTR-retrotransposon frequently found
associated to genes (promoter, terminator) which
modify the regulation of the expression of target genes
• On the other hand, the insertion of retrotransposons
in intergenic regions can also modify the expression of
adjacent genes eg-WIS 2 retrotransposon in wheat.

12. Contd….
• In rice Xa21gene family:
contains a high number of TEs (including LTR-
retrotransposons and MITEs) inserted within the different
genes, which evolve new resistance genes or the gene .
• TE insertion outside genes can also contribute to genome
evolution. Eg- used as MARs (functioning the neighboring
genes)
• Beside that plant centromere and pericentromeric regions
often contain retrotransposons that play a role in plant
chromosome organisation.
• In Maize the retotransposon interact with the kinetochore
protein CENH3

13. conclusion
• Cellular genes comprise at most 5-10% of cereal genomes rest
is retrotransposon primarily
• LTR retrotransposons present a major share of the genome,
contain conserved regions for which PCR primers may be
designed
• Retrotransposon’s insertions can be exploited as powerful
molecular markers systems for mapping, marker-assisted
breeding, phylogenetic analyses, biodiversity determinations,
and evolutionary studies.
• A high number of transposons are indeed activated by stress
and that their mobility has reshaped eukaryote genomes in
many ways.
• Vector design could be an additional tool based on intact
plant retrotransposon for transgenic plant development

15. Thank you
Thank you