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Pathogenesis v. symbiosis how do plants recognize beneficial organisms and not respond with defence activation?

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?. Major symbionts of plants include rhizobial bacteria and mycorrhizal fungi

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Pathogenesis v. symbiosis how do plants recognize beneficial organisms and not respond with defence activation?

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  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) Mycorrhizae - 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. http://commtechlab.msu.edu/sites/dlc-me/zoo/zdrr0125.html

  5. Gelvin (2000) Agrobacterium and plant genes involved in T-DNA transfer and integration. Ann Rev Plant Physiol and Mol Biol. 51:223-256

  6. 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 13:1019-1021

  7. 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

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

  9. RKN life cycle

  10. http://plantpath.caes.uga.edu/personnel/faculty/Hussey.html

  11. Enod40 and ces52 are induced during nodule formation and during Giant cell formation

  12. Phan and knox are induced during nodule formation and during Giant cell formation

  13. Weerasinghe RR, Bird DMcK, and Allen NS. (2005) Root-knot nematodes and bacterial Nod factors elicit common signal transduction events in Lotus japonicus. PNAS 102:3147-3152 nem factor (nemF) induces similar effects as nod factor and is also a small secreted molecule

  14. M. incognita nod-L • Protein sequence bacteria-like • 58% amino-acid identity (8.8e-54) to nodL from Rhizobium leguminosarum

  15. RKN nod-L Scholl, Thorne, McCarter, Bird. 2003. Horizontally transferred genes in plant-parasitic nematodes: A high-throughput genomic approach. Genome Biology, 4: R39.

  16. 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

  17. C. elegans H. glycines G. pallida G. rostochiensis M. chitwoodi ? M. hapla M. arenaria M. javanica M. incognita Detection of nod-L

  18. nodL O-acetylase Nod-L key enzyme for Nod factor biosynthesis

  19. 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?

  20. Weerasinghe RR, Bird DMcK, and Allen NS. (2005) Root-knot nematodes and bacterial Nod factors elicit common signal transduction events in Lotus japonicus. PNAS 102:3147-3152 nem factor (nemF) induces similar effects as nod factor and is also a small secreted molecule

  21. 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?

  22. 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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