A Bacterial Virulence Protein Suppresses Host Innate Immunity to Cause Plant

Disease

A Bacterial Virulence Protein Suppresses Host Innate Immunity to Cause Plant

DiseaseNomura, K., Debroy, S., Lee, Y.H., Pumplin, N., Jones, J., and He, S.Y. (2006).

Science 313, 220-223.

Presented by: Bob Berkey

Nomura, K., Debroy, S., Lee, Y.H., Pumplin, N., Jones, J., and He, S.Y. (2006). Science 313, 220-223.

Presented by: Bob Berkey

BackgroundBackground

Plants have evolved immune system to defend against microbial organisms that attempt to inject virulence proteins to suppress immunityMammalian pathogens can regulate cytoskeleton, membrane composition, vesicle trafficking, and host immunityNot much is known about molecular mechanisms of bacterial effector proteins in plantsBelieved effector proteins suppress the host immune responses

Plants have evolved immune system to defend against microbial organisms that attempt to inject virulence proteins to suppress immunityMammalian pathogens can regulate cytoskeleton, membrane composition, vesicle trafficking, and host immunityNot much is known about molecular mechanisms of bacterial effector proteins in plantsBelieved effector proteins suppress the host immune responses

Pseudomonas syringaePseudomonas syringae

Gram negative plant pathogenic bacteriumOver 40 pathovars of P. syringaethat can infect a variety of plant species including economically important ones like tomatoExamined strains all use Type III secretion system for pathogenesis

Associated hrp/hrc genesExchangeable effector locusConserved effector locus

Gram negative plant pathogenic bacteriumOver 40 pathovars of P. syringaethat can infect a variety of plant species including economically important ones like tomatoExamined strains all use Type III secretion system for pathogenesis

Associated hrp/hrc genesExchangeable effector locusConserved effector locus

Paper OverviewPaper Overview

Looking for the molecular targets of bacterial virulence proteins important in disease development, specifically PstDC3000HopM1, conserved P. syringae virulence protein, targets the immunity associated protein AtMIN7 in Arabidopsis

Mediates this through proteasome degradation

Results show strategy of pathogens that exploit proteasome to overrun immunity and cause disease symptoms

Looking for the molecular targets of bacterial virulence proteins important in disease development, specifically PstDC3000HopM1, conserved P. syringae virulence protein, targets the immunity associated protein AtMIN7 in Arabidopsis

Mediates this through proteasome degradation

Results show strategy of pathogens that exploit proteasome to overrun immunity and cause disease symptoms

Previous Work & InformationPrevious Work & Information

Partial deletion of conserved effector locus in ∆CEL mutant

reduction of bacterial population and elimination of disease symptoms (tomato and Arabidopsis)

Deletion is functionally redundant effector genes hopM1 and avrE

HopM1: 712 amino acid protein translocated into cell during infection by type III system

pORF43: plasmid expressing HopM1 and cognate chaperone ShcM

Partial deletion of conserved effector locus in ∆CEL mutant

reduction of bacterial population and elimination of disease symptoms (tomato and Arabidopsis)

Deletion is functionally redundant effector genes hopM1 and avrE

HopM1: 712 amino acid protein translocated into cell during infection by type III system

pORF43: plasmid expressing HopM1 and cognate chaperone ShcM

HopM1 Transgenic Expression Recovers Virulence of ∆CEL Mutant & Important Regions for Virulence

Function of HopM1

HopM1 Transgenic Expression Recovers Virulence of ∆CEL Mutant & Important Regions for Virulence

Function of HopM1

Figure 1

Figure S1

Pink arrows indicate the dominant negativeeffect of HopM11-200 and HopM11-300 on ΔCEL mutant. Blue arrows indicate the ability of full-length HopM1 or HopM1101-712 to completely or partially complement the ΔCEL mutant

The Dominant Negative Effect & Y2H Screens

The Dominant Negative Effect & Y2H Screens

Figure 2

Figure S2B

Destabilization of AtMIN Protein(s) Necessary for promotion of P. syringae

Pathogenesis by HopM1

Destabilization of AtMIN Protein(s) Necessary for promotion of P. syringae

Pathogenesis by HopM1

Figure 3

Figure S4B

BFA Can Supplement for HopM1 and Restore Virulence

BFA Can Supplement for HopM1 and Restore Virulence

ARF GEF proteins: key pats of vesicle trafficking systemBFA: well known inhibitor of vesicle trafficking

ARF GEF proteins: key pats of vesicle trafficking systemBFA: well known inhibitor of vesicle trafficking

Figure 3C

AtMIN7 Required for Cell Wall Associated Defense

AtMIN7 Required for Cell Wall Associated Defense

Callose deposition: cellular marker of cell wall defense

Callose deposition: cellular marker of cell wall defense

Figure 4

ConclusionsConclusionsHopM1 is necessary for the destabilization of AtMIN7, a host ARF GEF family protein active in host immune response, through the proteasomeRecent findings show a P. syringae effector protein AvrPtoB has intrinsic E3 ligase activity and that vesicle trafficking and extra cellular secretion are important in immune response

HopM1 does not show sequence homology to AvrPtoB or common motifs for components of ubiquitination/proteasome systemHopM1 probably functions as an adaptor protein that targets AtMIN7 to degradation pathway

HopM1 is necessary for the destabilization of AtMIN7, a host ARF GEF family protein active in host immune response, through the proteasomeRecent findings show a P. syringae effector protein AvrPtoB has intrinsic E3 ligase activity and that vesicle trafficking and extra cellular secretion are important in immune response

HopM1 does not show sequence homology to AvrPtoB or common motifs for components of ubiquitination/proteasome systemHopM1 probably functions as an adaptor protein that targets AtMIN7 to degradation pathway

P. Syringae ActionsP. Syringae ActionsEliminated component of vesicle trafficking pathway in order to suppress cell wall associated host defenseSalmonella enericaModulation of trafficking is a common goal of human and plant pathogens

Eliminated component of vesicle trafficking pathway in order to suppress cell wall associated host defenseSalmonella enericaModulation of trafficking is a common goal of human and plant pathogens

Figure S6

Possible Future DirectionsPossible Future Directions

GFP fluorescent tag studies of HopM1Only looked at Pst DC3000, do other P. syringae strains work in a similar manner in regards to AtMIN proteins particularly AtMIN7?Mechanisms of AtMIN7 targeting for degradation, and what protein(s) is HopM1 functioning as adaptor with?Similar function results seen in Arabidopsis from other bacterial pathogens?Other molecular targets of HopM1 since BFA treatment showed more complete virulence recovery than AtMIN7 KO?

GFP fluorescent tag studies of HopM1Only looked at Pst DC3000, do other P. syringae strains work in a similar manner in regards to AtMIN proteins particularly AtMIN7?Mechanisms of AtMIN7 targeting for degradation, and what protein(s) is HopM1 functioning as adaptor with?Similar function results seen in Arabidopsis from other bacterial pathogens?Other molecular targets of HopM1 since BFA treatment showed more complete virulence recovery than AtMIN7 KO?