PLANT INNATE IMMUNITY

1. ROLE OF SECONDARY METABOLITES
IN PLANT INNATE IMMUNITY
PAT- 613 DISEASE RESISTANCE IN
PLANTS (2+0)
K.SIVAGNANAPAZHAM
2018601508

2. SECONDARY METABOLITES
 Organic compounds produced by Bacteria,
Fungi or Plants which are not directly involved
in the normal growth ,development or
Reproduction of the organisms.
 Play an important role in plant defense
mechanisms.
 Important functions such as protection,
competition, and species interactions, but are
not necessary for survival.
 Examples:
Alkaloids,Antibiotics,Terpenoids,Quinolines,Ph
enazines, etc.

4. INNATE IMMUNITY
 Innate Immunity is an immunological subsystem
that comprises the cells and mechanisms that
provide the first line of defence from infection
in a non specific manner.
 Play immediately within the hours of a pathogen
enter in the body.
 Physical Barriers.
 Natural Immunity.

5. CLASSIFICATION
 Plant secondary metabolites can be divided into
three chemically distinct groups
Terpenes
Phenolics
Nitrogen & Sulphur containing
compounds.

7. TERPENES
 Largest class of secondary metabolites and are
united by their common biosynthetic origin from
acetyl - coA or Glycolytic intermediates.
 Five major classes
Mono
Sesqui
Di Terpenes
Tri
Poly
(Gerhenzon et al.,1991)

8. PHENOLIC COMPOUNDS
 Hydroxyl functional group on BENZENE ring.
 Chemically Heterogeneous group.
 Important part in Plant defense system such as
DISEASES
PESTS
ROOT PARASITIC NEMATODES
(Wuyts et al.,2006)

9. CLASSIFICATION
 Coumarin
 Furano – coumarin
 Lignin
 Flavonoids
 Iso flavonoids
 Tanins

10. 1.COUMARIN
 Simple phenolic compounds wides spread in
vascular plants and functions in various plant
defense mechanisms.
 SHIKIMIC ACID PATHWAY
 Common in Bacteria, Plants and Fungi absent in
Animals.
 Antifungal activity.
( Murray et al.,1982)

11. Contd…
 Halogenated coumarin derivatives work
effectively in invitro to inhibit Fungal growth.
Example:
 7 – hydroxylated simple coumarins -
parasitism of Orobanche cernua, by preventing
successful germination, penetration and
connection to the Host Vascular System.
(Serghini et al.,2001)

12. 2.FURRO COUMARIN
 Phyto toxicity to the palnts, in the family of
Umbelliferae (celery, parnsip,and parsley)
 Non Toxic to the plants until they activated by
the UV light.
 PSORALIN – a linear Furano - coumarin
known for its use in the treatment of Fungal
Defense.
 Found rarely in SO2 treated plants.
(Ali et al.,2008)

13. 3. LIGNIN
 Highly branced polymer of phenyl propanoid
groups.
 Physical toughness deters feeding by
herbivorous animals and its chemical durability
makes it relative to pathogens and insects.
 Lignification block the growth of pathogens
and are frequent response to infection or
wounding.
(Gould, 1983)

14. 4.TANINS
 Second category of Phenolic category of plant
phenolic polimers with defensive properties.
 Protocatechellic acid and chlorogenic acids –
Disease resistance of certain plants.
 They prevent Oninon smudge – Colletotrichum
circinans and prevent spore germination and
growth of fungi.
 Compounds readily formed oxidised into potent
fungistatic quinones by certain disease resistant
cultivars.
(Vickery, 1981; Butt and Lamb;Mayer,1987)

16. S containing secondary metabolites
 They include
GSH – Glutathione.
GSL – Glucosinolates.
Phytoalexins.
Thionins.
Defensins.
Allinin.
been directly or indirectly with the defense of
plants against Microbial pathogens – SIR.
(Crawford et al.,2000)

17. 1. GSH - GLUTATHIONE
 Regulation of plant growth and development –
stress responses.
 Act as a Anti oxidant.
 Detoxification of xenobiotics and cytokinins by
targeting them into a vacuole.
 Act as a systemic messenger carrying
information concerning the attack to non –
infested tissues.
 Specialized cell Trichomes secretes GSH.
(Choi et al.,2001)

18. 2. GSL - GLUCOSINOLATES
 S containing Glucosides produced in higher
plants.
 To increase resistance against the unfavourable
effect of predators, parasites, and competitors by
release of volatile compounds.
 Mustard oil Glucosides in cruciferaceae,
 Allyl cys sulfoxides in Allium- catalyse by
myrosinase , cleave glucose by S atom.
 Isothiocyanate, nitriles - defense.
(Siemens et al.,2009)

19. 3. DEFENSINS,THIONINS AND
LECTINS
 S rich non storage plant proteins synthesis and
accumulate after microbial attack.
 Some Defensins are antifungal or anti bacterial
activity.
 Defensins genes are partly pathogen inducible.(Gu
et al.,1992)
 Accumulation of Thionins in cell wall of infected
spikes shows Defense response against Fusarium
colmorum.
 Lectins defensive proteins that bind to
carbohydrate, after ingested by herbivores interfere
with nutrient absorption.
(Kang and Buchenauer,2003)

20. N containing secondary metabolites
 They include
Alkaloids
Cyanogenic Glucosides
Non protein Amino acids.
 Biosynthesized from amino acid.
 Role in anti herbivores defense and toxicity to
humans.

22. MECHANISMS
 For defense responses, biosynthesis and
activation of secondary metabolites are triggered
with the recognition of MAMPs by PRR by
Resistance proteins.
 Based on mode of biosynthesis and
accumulation of defense related phytochemicals
they classified as
PHYTOANTICIPINS
PHYTOALEXINS
(Ahuja et al.,2012)

23. PHYTOANTICIPINS
 Antimicrobial compounds that are performed
or become released from constitutively stored
precursors following attempts of microbial
invasion.
 Defensive metabolites produced and stored
constitutively in plant tissue are termed as
Phytoanticipins.
 Saponins,Glucosinolates,Cyanogenic
glucosides,Benzoxazinone glucosides.
(VanEtten et al.,1994)

24. 1. SAPONINS
 Saponins are glycosides of isoprenoid – type
aglycones usually representing triterpenoids or
steroids, widely distrubuted in flowering plants.
 Biosynthesis and invivo function of triterpenoid
saponin from oat species have been studied.
 Avenacins A-1,A-2,B-1,B-2.(roots)
 Absent in leaves.
 α- tomatine in TOMATO- steroidal
glycoalkaloid.
(Maizel et al.,1964,Arnerson 1968)

25. Contd…
 Avenacins and α-tomatine affect invitro growth
of a wide range of pathogenic and non
pathogenic fungi.
 Genetically screening of a chemicaIly
mutagenized Avena strigosa population
enabled the isolation of saponin – deficient
mutants. (sad mutants).
 SAD1,SAD2,SAD7 &SAD9 synthesis of
avenacins.
(Qi et al.,2006;Mugford et al.,2009,2013)

26. Contd…
 Roots of homozygous sad mutants susceptible to
adapted strain of soil borne fungus
Gaeumanonnomyces graminis
var.avenae,Fusarium culmorum and
F.avenaceum.
 Sad mutants revealed the susceptibility to non
adapted strain G.graminis var.tritici strain does
not infect oats
 Role of Avenacin play in Disease resistance.
(Papadopoulou et al.,1999)

27. 2.GLUCOSINOLATES
 Brassicales produced mainly.
 Derived from amino acids include
alanine,valine,leucine,isoleucine,methionine,
phenylalanine,tyrosin, tryptophan and
glutamic acid.
 Arabidiopsis thaliana accumulates two major
group of these compounds
 Methionine derived aliphatic glucosinolates
Tryptophan derived indolic glucosinolates
(Reichelt et al., 2002)

28. Contd…
 Glucosinolate hydrolysed by unstable
aglycogens β-thioglucoside
glucohydrolases(TGGs) (myrosimases).
 Results in the release of chemically unstable
aglycogens – isothiocyanate (ITC)
 AG derived ITCs insect deterrent properties,
restrict the growth of microbial pathogen.
(Brader et al.,2001)
 AG derived ITCs- Arabidopsis resistance
Bacterial pathogen pseudomonas syringae.
(Fan et al.,2011)

29. Immunity against Fungal pathogens
 Hemibiotroph- Phytophthora brassicae &
Colletotrichum species
 Nectrophic Ascomycete - Plectospharella
cucumerina
 Botrytis cinerea (Lipka et al.,2005)
 Magnaporthe oryzae
 Leptosphaeria maculans
 Piriformospora indica (Jacobs et al.,2011)

30. 3. CYANOGENIC GLUCOSIDES
 β-D-glucoside of α-hydroxy-nitriles derived from
tyrosine,phenylalanine,valine,isoleucine and
leucine.
 HCN gas contrast to antimicribial agents.
 Lima bean – Colletotrichum gleosporiodes
 Leucine derived CG epiheterodendrin- Barley
plants.
 Dhurrinase2(DHU2)- Sorghum bicolor.
(Nielsen et al.,2002)

31. 4.BENZOXAZINONE GLUCOSIDES
 Benzoxazinone glucosides (BXs)-Poaceae
including Maize,Rye,Wheat but not Barley
 Wheat & Maize – 2,4-dihydroxy-7-methoxy-
1,4-benzoxazin-3-one(DIMBOA-Glc)
 Rye & Barley - 2,4-dihydroxy-1,4-benzoxazin-
3-one(DIBOA-Glc).
 Antifungal activity against
G.graminis,F.moniliforme,F.culmorum &
Setosphaeria turcica.
 HDMBOA-Glc – F.graminearum,
B.mayids,C.lunata,& A.alternata.
(Ahmad et al.,2011)

32. PHYTOALEXINS
 Muller and Borger (1940).
 Low molecular weight anti-microbial
metabolites that are synthesized and accumulate
in plants after a pathogen challenge.
 Hundreds of Phytoalexins have been isolated
and characterized in different species.
 Selective groups include Camalexin
Phenylalanine derived, Terpenoids.
(Schmelz et al.,2014)

33. 1. CAMALEXIN (Brassicaceae)
 Sulphur containing tryptophan derived
alkaloids in response to pathogenic infection.
 Arabidopsis in defense responses.
 Genetic screening of an ethyl methanesulfonate-
mutagenized population revealed a series of 5
non allelic phytoalexin deficient (pad) mutants
with camalexin accumulation.
 Bioassay with P.syringae with both virulent and
Avirulent strains.
(Glazebrook et al.,1996)

34. Contd…
 Some PAD genes – encode protein with
regulatory function in Arabidopsis defense
pathways. PAD4 & PAD2
 Isolation of genes.
 PAD2 – γ-glutamylcysteine synthase involved in
Glutathione synthesis.
 PAD4- Disease response including Salicyclic
acid dependent signalling.
(Parisy et al.,2007)

35.  P.brassica, blockage of PEN2 pathway and
camalexin biosynthesis did not affect entry rates,
but led to more severe disease symptom than
observed in pen2 & pad3.
 Rapalexin A represents another S containing
indole alkoloid phytoalexin in Arabidiopsis.
 Biosynthesis is not obscure.
(Pedras &Yaya, 2013)

36. 2. PHENYLALANINE DERIVED
PHYTOALEXINS
 Many reported Phytoalexins under this group.
 Resveratrol- Grapevine, Arachis hypogea.
 Biosynthesis requires the enzyme- stilbene
synthase(STS)
 Precursor molecule- p-coumaroyl co enzyme A
& malonyl co A
 Grapevine STSgene VST1- promoter in Tobacco
leads to biosynthesis of Resveratol Disease
resistance to B.cineria.
(Hain et al.,1993)

37. Contd…
 Glyceollins – Soyabean
 Pisatin – Pea
 Medicarpin – Alfalfa
 Sakuranetin- Rice
 RNAi mediated silencing of isoflavone synthase
or chalcone reductase in soyabean leads to
resistance.
 HopZ1 effector protein in TYPE 3 Cell in
Bacteria – Resistant against P.syringae.
(Zhou et al.,2011)

38. 3.TERPENOIDS
 Momilactones A&B – Rice First identified
members of this group.
 Diterpenoids Phytoalexins – Oryzalexins,
Phytocassanes.
 20 genes linked to diterpenoid phytoalexin
biosynthesis in rice were investigated.
 Genes encode
Class 2 – (copalyl diphosphate synthases)
Class 1 – (kaurene synthase like) & P450
Monooxygenases.
(Peters,2006;Schelz et al.,2014)

39. Contd…
 CPS4 – biosynthesis of Momilactones &
Oryzalexins
 CPS4 along with T-DNA insertion plant
produces Momilactones & Oryzalexins
 Resistant against M.oryzae & F.fujikuroi.
 Maize also produces a large number of terpenoid
phytoalexins include
Kauralexins
Sesquiterpenoids Zealexins
(Huffakar et al.,2011)

41. CONCLUSION
 Majority of these compounds our knowledge
about the details of their biosynthesis and
contribution to plant immunity scarce.
 Increasing the number of plant genome
sequences available and further significant
improvement in molecular biology techniques.
 Possible to generate gene cassettes for complete
pathways –production of valuable secondary
metabolites.