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Pathogenesis v. symbiosis

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Pathogenesis v. symbiosis how do plants recognize beneficial organisms and not respond with defence activation? how do symbionts recognize and communicate with a host? – PowerPoint PPT presentation

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Title: Pathogenesis v. symbiosis


1
  • Pathogenesis v. symbiosis
  • how do plants recognize beneficial organisms and
    not respond with defence activation?
  • how do symbionts recognize and communicate with
    a host?
  • do commonalities exist?

2
Major symbionts of plants include rhizobial
bacteria and mycorrhizal fungi Rhizobia -
Nitrogen fixation (specific to legumes) Mycorrhiz
ae - Nutrient uptake, protection from pathogens
(most plants) Both initially induce plant
defenses short lived localized to few cells
3
  • Plants must first recognize colonization by the
    symbiont
  • elicitors may be exogenous (produced by
    symbiont)
  • or endogenous (produced by the host)
  • synthesis of chalcone synthase and phytoalexins
  • in legumes induced by mycelial extracts!
  • nod factor
  • SA, ROS induced, but short lived
  • suppression or degradation?
  • 2 possibilities
  • symbionts produce weak response
  • down regulation accomplished by further
    crosstalk

4
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5
http//commtechlab.msu.edu/sites/dlc-me/zoo/zdrr01
25.html
6
(No Transcript)
7
(No Transcript)
8
Gelvin (2000) Agrobacterium and plant genes
involved in T-DNA transfer and integration. Ann
Rev Plant Physiol and Mol Biol. 51223-256
9
(No Transcript)
10
Bittinger MA, Gross JA, Widom J, Clardy J, and
Handelsman J. (2000) Rizobium etli CE3 carries
vir Gene Homologs on a Self-Transmissilbe
Plasmid. MPMI 131019-1021
11
Four major events are important in activating and
suppressing plant defense during the interaction
of plants and benficial symbionts
  • Plant recognition of the symbiont
  • Signal transduction
  • Activation and expression of plant defense genes
  • Suppression of plant defense genes/degradation of
  • Elicitor molecules

12
  • Nematodes and nodules
  • root-knot nematodes share a common pathway with
    rhizobia,
  • yet are pathogenic!

13
RKN life cycle
14
http//plantpath.caes.uga.edu/personnel/faculty/Hu
ssey.html
15
Enod40 and ces52 are induced during nodule
formation and during Giant cell formation
16
Phan and knox are induced during nodule formation
and during Giant cell formation
17
Weerasinghe RR, Bird DMcK, and Allen NS. (2005)
Root-knot nematodes and bacterial Nod factors
elicit common signal transduction events in Lotus
japonicus. PNAS 1023147-3152
nem factor (nemF) induces similar effects as nod
factor and is also a small secreted molecule
18
M. incognita nod-L
  • Protein sequence bacteria-like
  • 58 amino-acid identity (8.8e-54) to nodL from
    Rhizobium leguminosarum

19
RKN nod-L
Scholl, Thorne, McCarter, Bird. 2003.
Horizontally transferred genes in plant-parasitic
nematodes A high-throughput genomic approach.
Genome Biology, 4 R39.
20
M. incognita nod-L
  • Protein sequence bacteria-like
  • 58 amino-acid identity (8.8e-54) to nodL from
    Rhizobium leguminosarum
  • Gene structure typical of a nematode
  • 2 introns
  • mRNA trans-spliced at the 5-end polyadenylated
    at the 3-end
  • eukaryotic promoter
  • codon usage (codon adaptation index)
    nematode-like, not rhizobia-like

21
Detection of nod-L
22
Nod-L key enzyme for Nod factor biosynthesis
23
nod-L in RKN
  • What is the function of this gene in RKN?
  • Does RKN make a Nod factor?
  • Does the RKN-plant interaction have similarities
    to the rhizobia-plant interaction?

24
Weerasinghe RR, Bird DMcK, and Allen NS. (2005)
Root-knot nematodes and bacterial Nod factors
elicit common signal transduction events in Lotus
japonicus. PNAS 1023147-3152
nem factor (nemF) induces similar effects as nod
factor and is also a small secreted molecule
25
nod-L in RKN
  • What is the function of this gene in RKN?
  • Does RKN make a Nod factor?
  • Does the RKN-plant interaction have similarities
    to the rhizobia-plant interaction?
  • How did RKN acquire nod-L?
  • Horizontal gene transfer?
  • Does RKN have other rhizobial-like genes?

26
Other horizontal candidates?
  • Global search of the Meloidogyne EST set
  • MI00754 - 2-hyrdoxymuconic semialdehyde hydrolase
  • MI00252 - exo-polygalacturonase
  • MI00426 - glutamine sythetase
  • MI01644 - L-threonine aldolase
  • MI00109 - hypothetical conserved protein
  • b-endoglucanases (ancient paralogues)
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