This is a presentation on Horizontal gene transfer(HGT) in evolution of nematodes which gives us idea about importance of HGT in evolution of nematode parasitism. Here I have covered the historical events about HGT as well. This is my First seminar in Div of Nematology.

2. Horizontal Gene Transfer
in Evolution of Nematode Parasitism
Priyank H. Mhatre
Roll No - 5021
Division of Nematology

3. Gene
A gene is a unit of heredity in a
living organism
It is a segment of DNA that code
for a specific protein
Genes hold the information to
build
and
maintain
an
organism's cells

4. What is Gene Transfer?

5. Types of Gene Transfer
Vertical gene transfer
Horizontal gene transfer

6. Vertical Gene Transfer
Vertical Gene Transfer : transmission of genes from
an organism to it’s offspring
- Sexual reproduction in higher
animals and plants is the way
of VGT

7. Horizontal gene transfer
Horizontal gene transfer (HGT) - implies the non-sexual
exchange of genetic material between species, in some
cases even across kingdoms

8. History of HGT
Frederick Griffith (1879-1941)
Joshua Lederberg (1925-2008)

9. Cont…
 Frederick Griffith in 1928 first time seen the transformation in
bacteria

J Lederberg in 1946 – 47 first time seen conjugation and in 1956
transduction in bacteria

M Syvanen (1985 ) proposed this mechanism as cross-species
gene transfer in evolution

Hilario & Gogarten (1993 ) use the term horizontal gene
transfer between organisms as an alternative explanation for
those conflictive phylogenetic events
(Luis Boto., 2009)

10. Some facts…
HGT is the non-genealogical transmission of genetic
material from one organism to another
It is a source of new genetic material to the recipient
It is a mechanism that permits the acquisition of
evolutionary novelties
It is common mechanism of gene transfer in bacteria
and archaea
(Luis boto., 2009)

11. Types of HGT
Ancient
HGT
Recent

12. Types of HGT
Ancient
:- genes transferred between organisms separated a long time
ago
-The ancient HGT is difficult to detect through codon usage bias and
differential base composition
Foreign
genes in
cell
once
they are
part of the
same
genome
support
same
mutational
bias with
resident
and
ameliorated
after many
generations
Recent :- genes transferred between organisms separated
recently
- Easy to detect based on Criteria of codon usage bias and
differential base composition.
(Luis Boto., 2009)

13. How it happens?
Transformation
HGT
Transduction
Conjugation
Transduction

15. Magic of
Horizontal Gene Transfer

16. The photosynthetic sea slug Elysia chlorotica appears like a dark green leaf as a
result of retaining chloroplasts from its algal prey, Vaucheria litorea, in cells lining
of its digestive tract.
The sea slug has acquired photosynthesis-supporting genes by horizontal gene
transfer and can use the chloroplasts to carry out photosynthesis for several months
(Rumpho et al., 2008)

17. How It Grows?
(Rumpho et al., 2008)

18. Cont…
It is also called as “solar-powered” sea slug
Nuclear gene of oxygenic photosynthesis, psbO, have been
acquired by the animal via HGT
Photosynthesis is by the plastids which provides E.
chlorotica with energy for its entire lifespan of ∼ 10 months
The plastids are not transmitted vertically (i.e. are absent in
eggs) and do not undergo division in the sea slug.
(Rumpho et al., 2008)

19. What about nematodes?

20. Evolutionary History of Nematodes
Era
Period
Millions Year ago
CENOZOIC
MESOZOIC
Cretaceous
Jurassic
Triassic
65 --- Flowering plants (PPN)
145
200
PALEOZOIC
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
253--- Insect (EPN)
300
336
440
484 Land Plants
542 --- Nematodes origin (FLN)

21. Evolution of Parasitism In Nematodes
Free-living
Phoresy
Necromeny
Pre-adaptations1. Dauer larvae
2. Toxicity tolerance
3. Low oxygen tolerance
Parasitism
(Dieterich et al., 2009)

22. Pristionchus pacificus
Found in a necromenic association with scarab beetle representing an
intermediate type of association between phoretic and parasites
This intermediate association considered as a step toward parasitism
In this nematode the number of detoxification enzymes are Increase,
in comparison to phoretic nematodes
It has also acquired cellulase genes Ppa-cel-1, 2, & 3 via HGT from
bacteria and archaea
This is the first report of cellulase found in non plant parasitic
nematodes
(Mayer et al., 2011)

23. Nematode proteins with their activity
Enzymes
Cellulase,
Xylanases
Activity
Degradation of cellulose and
hemicelluloses
Polygalacturonases,
Pectate lyases,
Degradation of pectins
Candidate arabinanases
Expansin
Soften the plant cell wall
(Danchin et al., 2010)

24. Plant cell wall modifiers with their closest
relatives
(Danchin et al., 2010)

25. Phylogenetic Analysis of Polygalacturonases, Pectate
lyases, Candidate arabinases
(Danchin et al., 2010)

26. Phylogenetic Analysis of Cellulase, Xylanases., and
Expansin.
(Danchin et al., 2010)

27. Cellulase in nematodes
Cellulases are enzymes that hydrolyse the β-1,4 linkages of cellulose
These genes are acquired via HGT from bacteria, fungus, or other
microbes
Cellulases are from three structurally and phylogenetically unrelated
families found in nematodes :1. GHF5- genes common in PPN
2. GHF16- genes are known from B. xylophilus , B. mucronatus
3. GHF45- genes are known from B. xylophilus

28. GHF5

29. Cyst Nematodes
1st report of genes with endogenous cellulase production by animals
in absence of cellulolytic microorganisms was in G. rostochinensis
and in H. glycines
Genes - GR-eng-1 and 2, HG-eng-1 and 2 - oesophageal gland
Protein- GR-ENG-1 & 2, HG-ENG-1 & 2 – stylet secretion
These genes facilitate the intracellular migration of nematodes
through plant roots by partial cell wall degradation
These genes show homology with genes of the bacteria like Erwinia
chrysanthemi, Clostridium acetobutylicum and B. subtilis
( Smant et al., 1998 )

30. RKN (M. incognita)
Researchers characterized a new β-1,4-endoglucanase gene from
the root-knot nematode
They identified the gene - MI-eng-2, which is localized in the
secretory oesophageal glands cell of all developmental stages of
the nematode and the protein secreted is– MI-ENG-2
This protein is involved in plant cell wall degradation during
parasitism
GHF5 genes result from horizontal gene transfer of a bacterial
gene with a cellulose-binding domain (CBD)
(Ledger et al.,2006)

31. ResultsRT-PCR
Uninfected tomato roots
Lemmi9 primers
Unhatched coiled juveniles
Freshly hatched J2s
Females
Males
(Ledger et al.,2006)

32. Cont…
In situ hybridization
This picture shows that MI-eng-2 gene is present in sub-ventral oesophageal
glands of M. incognita
(Ledger et al.,2006)

33. Evolution of Cellulase Genes
Linker domain
Catalytic domain
CBD
(Ledger et al.,2006)

34. GHF16

36. Bursaphelenchus
Large group of nematodes
Worldwide distributed
Most species are solely fungal feeders and all species rely on
fungi as a food source at some stage of their life cycle
B. xylophilus - Unique feeding habit i.e. feed on live trees &
fungus (both)
(Kikuchi et al., 2005)

37. β-1,3-glucanase in pine wilt nematode
β-1,3-Glucanases catalyse the hydrolysis of β-1,3-D-glucosidic
linkages in β-1,3-D-glucan
This polymer (β-1,3-glucan ) is a major structural component of
fungal cell walls thus the protein is allowing the nematodes to
feed on fungus
This shows that β-1,3-glucanases play an important role in the
life cycle of this nematode
(Kikuchi et al., 2005)

38. Cont…
Enzymes with their Glycosil Hydrolase FamiliesBacterial , Nematodes - GHF 16
Plant and fungus- GHF 17
Sequences shows that Pinewood nematode B. xylophilus has
acquired endo-β-1,3-glucanase (GHF16) by HGT from bacteria
like Xanthomonas axonopodis , Pseudomonas spp. etc
(Kikuchi et al., 2005)

39. RESULTS
Southern-blot analysis
in situ hybridization
Southern-blot analysis of Bx-lam16A Genomic
DNA from B. xylophilus (N) and B. cinerea (F)
were digested with EcoRI (lanes 1 and 3) or
HindIII (lanes 2 and 4). The blot was
hybridized with a probe generated from Bxlam16A cDNA
Localization by in situ hybridization of Bx-lam16A
transcripts in the oesophageal gland cells of
B.
xylophilus adult female with antisense (A) and sense (B)
Bx-lam16A digoxigenin - labelled cDNA probes
(Kikuchi et al., 2005)

40. Phylogenetic tree of selected GHF16
Phylogenetic tree of selected GHF16 β-1,3-glucanases and β-1,3-glucanase-like proteins
generated using maximum-likelihood analysis
(Kikuchi et al., 2005)

41. GHF45

42. Life Cycle of B. xylophilus

43. GHF 45
B. xylophilus is part of clade of PPN (RKN
& CN) and not directly related to FFN
As this nematode feed on fungus, some
genes are horizontally transmitted to the
ancestor by fungus
Researchers identified a cellulase gene:
Bx-eng-1 from this nematode which is from
GHF 45 and is similar to the fungus
Southern- blot Analysis of Bx-eng-1 digested
with EcoR1 or HindIII and the blot was
hybridized with a probe generated from Bxeng-1 cDNA.
Southern- blot Analysis
of Bx-eng-1
(Kikuchi et al., 2004)

44. in situ hybridization
Localization of Bx-eng-1 transcripts in the oesophageal gland cells of B. xylophilus adult
female by in situ hybridization. Nematode sections were hybridized with antisense (A) or
sense (B) Bx-eng-1 digoxigenin- labelled cDNA probes
(Kikuchi et al., 2004)

45. Evolution of Heterorhabditis-Photorhabdus symbiosis with a
marine Lux operon
Squid with Lux
operon came at
seashore
Rhabditid enters in
it & quiescence
occurs
Bacteria start
feeding on dead
squid
Nematode feed on
bacteria in carcass
(Necromeny)
Endosymbiotic and
squid bacteria
mingle
Lux gene acquired
by endosymbiotic
bacteria
(Poinar, 1993)

46. Filarial worm with endosymbionts DNA
Wolbachia is a symbiont in the most filarial
worm
Infected filarial nematodes depend on
Wolbachia for proper development and
survival
Two Filarial species Acanthocheilonema
viteae and Onchocerca flexuosa were
found without Wolbachia but with DNA of
Wolbachia
Wolbachia
DNA
Researchers identified 49 Wolbachia-like
DNA sequences in A. viteae and 114 DNA
sequences in O. flexuosa
(McNulty et al., 2010)

47. HGT is an important evolutionary novelty present in nature
Nematode acquired several parasitic genes by horizontal gene
transfer from bacteria, fungus & other microbes to become a
potential parasite of plant, animals and other invertebrates
Because of HGT Pine wilt nematode got a unique capacity to feed on
both live plants and fungi

48. Heterorhabditid formed a symbiotic association with Photorhabdus
and evolved as EPN
Some filarial worms are able to survive without Wolbachia as they have
acquired DNA of Wolbachia via HGT which plays an important role in
their development & survival