Title: Whats a plant They have pathogens And immunity
1 Whats a plant They have pathogens And immunity 2 (No Transcript) 3 Tobacco mosaic virus (TMV)
RNA virus discovered by Beijerinck over 100 years ago as a contagium vivum fluidum that was filterable and could move through agar media. (Bacteria were not filterable and remained fixed in agar).
CTMV causes mosaic disease in tobacco and other plants.
Widely used in host-pathogen research.
4 (No Transcript) 5 (No Transcript) 6 Why TMV
Mosaic disease of tobacco was detrimental to the tobacco industry in the early 1900s.
Mayer in 1886 in the Netherlands was the first to artificially transmit a plant disease (TMV) the causal agent of which could not be seen or cultured.
Around the same time Pasteur was having a similar problem with rabies!
7 Model Systems
Models become the driving force for independent steps of discovery intervention and development.
TMV rapidly accumulates to high titres in infected plants.
TMV is not transmitted by insects fungi or nematodes but is by rub-inoculation.
TMV symptoms are easy to identify and can infect a wide range of plants.
8 TMV in the laboratory
Easy cheap and reliable to produce.
Omega leader sequence has been widely used to enhance translation of foreign genes in transgenic plants.
cDNA copies of TMV promoters have been used in gene vectors for expression of foreign genes in rub-inoculated plants.
9 (No Transcript) 10 Pathogenic Plant Bacteria
Pseudomonas syringae pv. tomato DC3000
Bacterial speck disease caused on tomato and mustard plants.
gt30 Type III Secretion
11 Arabidopsis thaliana
Just as animal biologists and medical researchers have used model organisms such as Drosophila and the nematode so plant biologists have relied upon the mustard Arabidopsis thaliana to help them understand the genetics physiology development and structure of plants in general.
Although the efforts of Arabidopsis sequencers have perhaps been less heralded than those of their colleagues working on animal genomes the results they have yielded are no less scientifically interesting. Arabidopsis may be a simple plant (its detractors call it a weed!) with only 50 identified cells types and no complex nervous system or behavioural response but its genome is surprisingly complex. Chromosomes 2 and 4 of Arabidopsis were published in Nature at the end of 1999 now followed by chromosomes 1 3 and 5.
Hypersensitive Response (HR) induces Programmed Cell Death (PCD).
13 Pseudomonas DC3000
Full genome has been sequenced.
DC3000 elicits HR immunity (via apoptosis) in plants carrying Pto R proteins (serine/threonine kinase).
Plant Pto interacts with bacterial DC3000 AvrPto and AvrPtoB effectors as well as Prf for HR response and plant immunity.
14 Plants without Pto protein
Without Pto the effectors AvrPto and AvrPtoB promote bacterial growth!
AvrPto suppresses cell wall-based defenses.
AvrPtoB has Cell Death Suppressor (CDS) activity to prevent HR-based PCD (apoptosis).
Belongs to VirPphA gene family.
VirPpha is a virulence factor located on a large Pph plasmid.
VirPpha and AvrPtoB have 51 sequence identity so they are most likely related but not homologous proteins.
AvrPtoB is bigger than AvrPto but has a similar interaction with Pto.
16 Cell Death Suppression
AvrPtoB CDS was discovered with Nicotiana because of its robust cell death response.
AvrPto with Pto results in PCD but AvrPtoB with Pto in Nicotiana did not result in Programmed Cell Death!
Mutant and pro-apoptotic experiments with AvrPtoB supported CDS activity.
Hidden R gene discovered
Rsb Resistance Suppressed by the avrPtoB C-terminus involved in CDS activities.
17 (No Transcript) 18 DC3000 Pathogenesis
Wild type tomato plants with AvrPtoB and without functional pto gene CDS.
Mutant AvrPtoB led to PCD and immunity.
Introducing AvrPtoB in trans restored virulence of DC3000 and CDS!
19 Rsb gene
AvrPtoB must be recognized by at least two resistance genes. Rsb is Pto related
Like Pto Rsb is Prf dependent for CDS.
Gene silencing experiments of Pto family members eliminates Rsb resistance in tomatoes and PCD in Nicotiana plants.
20 (No Transcript) 21 Other DC3000 Effectors
HoPtoD2 HopPtoE HopPtoF HopPtoN AvrPphE AvrPpiB1
Cell Death Suppression activity is not specific and can inhibit various R proteins.
Most effectors were discovered based on eliciting the HR immune response but they also have the potential for CDS activity.
22 Trump Model
Not the Donald thank goodness!
The host-pathogen interaction may involve an R protein as well as a Trump factor that can suppress the CDS activity.
This model accounts for the hidden resistance genes and complex plant-bacteria interactions.
23 Trump Model Version 1
The CDS effector is dominantly expressed if R protein but no T factor is present.
24 Trump Model Version 2
CDS effector is suppressed if both R protein and T factor are present.
25 Trump Model Version 3
CDS effector is dominantly expressed if T factor but no R protein present.
26 Other Virulence Activities
DC3000 mutants without CDS activity cause a 10-fold growth decrease in tomato plants.
Plants with prf mutations cannot mount Pto- or Rsb-mediated immunity.
AvrPtoB can activate ethlyene production in tomato plants increasing cell death.
27 Why would bacteria evolve to both enhance and suppress cell death
Perhaps early in infection it is advantageous to suppress PCD to escape the immune system and establish the infection.
Later in the infection it may be advantageous to enhance PCD to gain access to new cells and nutrients.
28 (No Transcript) 29 Phytophthora ramorum
First observed causing bleeding stem cankers and mortality of tanoak and coast live oak in coastal CA in the 1990s it has now been identified in North America and Europe.
Mortality associated with Fagus genus but foliar and twig infections of other species are important for pathogen spread.
30 (No Transcript) 31 Sudden Oak Death Research
Individual tree level
32 Forest Succession
Mosaic landscapes provide a variety of niches and microclimates.
Successional stages follow disturbances such as fire or logging.
Tanoak sprouts prolifically following fire and is later replaced by Douglas-fir or coast redwood trees.
33 (No Transcript) 34 (No Transcript) 35 (No Transcript) 36 (No Transcript) 37 (No Transcript) 38 (No Transcript) 39 The End!
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