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?
2Major 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
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5http//commtechlab.msu.edu/sites/dlc-me/zoo/zdrr01
25.html
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8Gelvin (2000) Agrobacterium and plant genes
involved in T-DNA transfer and integration. Ann
Rev Plant Physiol and Mol Biol. 51223-256
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10Bittinger 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
11Four 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!
-
13RKN life cycle
14http//plantpath.caes.uga.edu/personnel/faculty/Hu
ssey.html
15Enod40 and ces52 are induced during nodule
formation and during Giant cell formation
16Phan and knox are induced during nodule formation
and during Giant cell formation
17Weerasinghe 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
18M. incognita nod-L
- Protein sequence bacteria-like
- 58 amino-acid identity (8.8e-54) to nodL from
Rhizobium leguminosarum
19RKN nod-L
Scholl, Thorne, McCarter, Bird. 2003.
Horizontally transferred genes in plant-parasitic
nematodes A high-throughput genomic approach.
Genome Biology, 4 R39.
20M. 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
21Detection of nod-L
22Nod-L key enzyme for Nod factor biosynthesis
23nod-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? -
24Weerasinghe 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
25nod-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?
26Other 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)