Fred Gildow and Padmini Herath contributed to this lecture Cell wall Cytoplasm of sieve tube element Phytoplasma Mycoplasmas humans amp animal pathogens 2 Spiroplasmas ID: 446131
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Slide1
Mollicutes
Fred Gildow and Padmini Herath contributed to this lecture
Cell wall
Cytoplasm of
sieve
tube element
PhytoplasmaSlide2
Mycoplasmas
- humans & animal pathogens
2.
Spiroplasmas
- spiral shape - culturable
- plant pathogens (corn stunt)
3. Phytoplasmas
- circular, oval, tubular
- plant pathogens
Kingdom: Prokaryote
Class:
MollicutesSlide3
Phytoplasma & Spiroplasma
Saskia
Hogenhout
: http://www.oardc.ohio-state.edu/phytoplasma/
Plant Pathogens!Derived from gram +
bacteriaNo cell wall:Mollis = soft
Cutis = skinNo flagellaPlant pathogenic: phloem specific
Vectored in
Circulative
propagative mannerSlide4Slide5
Spiroplasma Example
Corn Stunt DiseaseSouthern US, Central and South AmericaYellow streaks on young leavesOlder leaves turn
purpleStunting – reduced distance between nodes
Sterile tasselsMany small, seedless ears
Movement
Colonies on agarSlide6
Corn StuntSlide7
Phytoplasmas: The Discovery
Studied Mulberry dwarf diseaseYears of work – no biological agent discovered
EM found no viruses
as expectedVeterinarian colleague noted structures similar to mycoplasma
Accidental discovery - cross disciplinary advantageConcluded mulberry dwarf caused by:
Mycoplasma-Like Organism (MLO) Similar structures then seen associated with Aster yellows disease
Doi
, Y, et al., 1967. Annals of the Phytopathological Society of Japan.Slide8
Koch’s Postulates Never Completed. Phytoplasma association proven by…
Pleomorphic, membrane-bound cells occurred only in phloem sieve elements of diseased plants, not in healthy plants
Morphology
was similar to mycoplasma
infecting animalsTetracycline
causes symptom remission and disappearance of phytoplasma cells (MLO)Penicillin had no effectPenicillin inhibits bacterial wall formation (outer layer)Slide9
Phytoplasma Characteristics
75+ distinct phytoplasmasCause over 600 diseases in 700 plant speciesAmorphous shape
Ranging from 70-1000 nm in diameter.
Similar to chloroplastAsexual reproduction: buddingIn plant and insect (vector) cytoplasm
General disease symptoms…Chlorosis and reddeningShortening of internodes (stunting)
Loss of apical dominance (witches’ broom)
Peach X
Lethal Palm YellowingSlide10
Important Phytoplasmas
Aster YellowsOrnamentals and vegetable crops
Elm Yellows
(Elm Phloem Necrosis)Eastern US - finishing off the elms (DED)
Branch-inducing
phytoplasmaPoinsettiaAsh Yellows (Ash decline)
USA- forest and nursery epidemicsSlide11
Aster Yellows
Host range: 200+ dicots, over 40 plant familiesVegetables, Flowers, Ornamentals, WeedsOverwinter in dandelion, thistleSymptoms:
Witches’ brooms
, woolly 2
o roots, stunted and tapered.Bad taste!
Periwinkle:Chlorosis
, dwarfingPhylloidy: flowers develop as vegetative tissue (Horomone disruption)
CarrotSlide12
Aster Yellows in vivo (plant host)
Sieve plate
S.T.E. cell 1
S.T.E. cell 2
Phytoplasma
Phytoplasma
in phloem
sieve tube element
at sieve plate passing between adjacent cells
Phloem necrosis
- sieve elements eventually die, blocking carbohydrate translocation in plant.Slide13
Phloem
Stylet
Epidermis
Mesophyll
Aster yellows
Transmitted by:
Grafting, budding
Aster Leafhopper
Circulative
Propagative
!Slide14
Phytoplasmas
hit home…
ELM YellowsSlide15
Elm Yellows (Elm Phloem Necrosis)
Candidatus Phytoplasma ulmiSymptoms:Fine, fibrous roots die 1
st
Chlorotic leaves (as roots die)Brownish-yellow discoloration of phloemPhloem sieve cells partially filled w/
callose (hard, gummy carbohydrate) Wintergreen odor when cut (American Elm)Maple syrup odor for red elm
Defoliation and death (within one year)Slide16
Elm YellowsSlide17
Under bark: Necrosis of the phloemSlide18
Vector: white-banded leafhopperCirculative (persistent) -
Propagative Latent period (10-45 days) Phytoplasma must infect salivary glands before transmissionLay eggs in Elm bark (overwinters)EY not transmitted to eggs
Through root grafts
Phloem connectionsPollen/seed transmission unknown
EY Transmission
www.na.fs.fed.us
Nymph
Adult
Slide19
Control of Elm
Yellows:
Slow epidemic rate (r)
Tetracycline
Injections
Antibiotic puts disease in
remission
But EY
Elms will die, cannot be “saved”
Tetracycline is produced
by
Streptomyces sp.
(Brand
names:
Achromycin
,
Sumycin
)
Removal
of infected trees:
Reliable ID system developed at Penn State
Continuous scouting
Break up
root grafts
Insecticides
to control vector… efficiency?
European elms
more resistant to EY
But susceptible to DED
Double-edged swordSlide20
Old Main
Elm yellows on
PSU campus
Padmini
Herath
26/342 Elms infected
WB leafhopper not foundSlide21
Poinsettia
Euphorbia
polcherrimaSlide22
Poinsettia
Native to tropical Central Am. And MexicoIntroduced to US by Joel Robert Poisette in 1825.1st US Ambassador to Mexico.In the wild – a 10ft tree.
Extensive breeding: 2 commercially grown types:
Free-branching
Developed in 1923 by Paul Ecke in CA
Deemed more desirablePerfect bractsFoliage retentionRestricted (strong apical dominance)Slide23
What Causes Branch Induction?
Free-branching (FB) characteristic disappeared following heat treatment/ meristem tissue culture…
These treatments are used in breeding to eliminate pathogens (such as viruses)Branching restored when treated plants were
grafted onto FB rootstock. Originally thought poinsettia mosiac virus was cause…
No, it was found in both restricted and FB typesELISA confirmed no virus in FB plantsSlide24
Free Branching… Look Familiar?
Restricted
Free Branching
Aster Yellows in carrotSlide25
Proof of
pathogenicity
Transmitted
phytoplasma from FB poinsettia to periwinkle.Connected vascular tissues using dodder as a bridge.
Then, transmitted phytoplasma
into to Restricted poinsettia from periwinkle.Observed branching-induction!Lee et al. 1995. Nature
Biotechnology. 15: 178-182Slide26
Poinsettia Branch-Inducing Phytoplasma
Free-branching is a symptom!Not economically detrimentalPBIP not found in other plants in nature.Related to phytoplasma
that causes Peach X disease.Insect vector not known.
Poinsettias can also be infected with Peach X and Aster YellowsUndesirable!Slide27
Food for Thought…
Phytoplasma in poinsettia is desirableColor-breaking tulipsPotyvirusAre these poinsettias/tulips diseased?Are these organisms beneficial?Symbionts or pathogens?
Friend or foe?Slide28
In-class Exercise:Phytoplasmas in the News
Read your article.Discuss with your group:Was article factual?Info on phytoplasmas
correct/informative?Did you find any scientific errors?
What info should be added to make the piece more helpful to the public, informative or correct?If you were contacted by a media outlet, as a phytoplasma expert, what would you add to the article?
Present your ideas to the class.