Post on 22-Dec-2015
transcript
MOLLICUTES
Fred Gildow and Padmini Herath contributed to this lecture
Cell wall
Cytoplasm ofsieve tube element
Phytoplasma
1. Mycoplasmas
- humans & animal pathogens
2. Spiroplasmas
- spiral shape
- culturable
- plant pathogens
(corn stunt)
3. Phytoplasmas
- circular, oval, tubular
- plant pathogens
KINGDOM: PROKARYOTECLASS: MOLLICUTES
PHYTOPLASMA & SPIROPLASMA
Saskia Hogenhout : http://www.oardc.ohio-state.edu/phytoplasma/
Plant Pathogens!
Derived from gram + bacteria
No cell wall:
Mollis = soft
Cutis = skin
No flagella
Plant pathogenic: phloem specific
Vectored in Circulative propagative manner
Phytoplasma
•Circular, oval, tubular•Unculturable•Obligate biotroph•Koch’s postulates not completed
Spiroplasma
•Helical,spiral•Culturalable•Facultative saprophyte•Koch’s postulates performed. •Motile – corkscrew action.
SPIROPLASMA EXAMPLE
Corn Stunt Disease
Southern US, Central and
South America
Yellow streaks on young
leaves
Older leaves turn purple
Stunting – reduced
distance between nodes
Sterile tassels
Many small, seedless ears
Movement
Colonies on agar
PHYTOPLASMAS: THE DISCOVERY
Studied Mulberry dwarf disease
Years of work – no biological agent discovered
EM found no viruses as expected
Veterinarian colleague noted structures similar to mycoplasma
Accidental discovery - cross disciplinary advantage
Concluded 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.
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 animals
Tetracycline causes symptom remission and disappearance of phytoplasma cells (MLO)
Penicillin had no effect Penicillin inhibits bacterial wall formation (outer layer)
PHYTOPLASMA CHARACTERISTICS 75+ distinct phytoplasmas
Cause over 600 diseases in 700 plant species
Amorphous shape
Ranging from 70-1000 nm in diameter.
Similar to chloroplast
Asexual reproduction: budding
In plant and insect (vector) cytoplasm
General disease symptoms…
Chlorosis and reddening
Shortening of internodes (stunting)
Loss of apical dominance (witches’ broom)
Peach X
Lethal Palm Yellowing
IMPORTANT PHYTOPLASMAS
Aster YellowsOrnamentals and vegetable crops
Elm Yellows (Elm Phloem Necrosis)Eastern US - finishing off the elms (DED)
Branch-inducing phytoplasmaPoinsettia
Ash Yellows (Ash decline)USA- forest and nursery epidemics
ASTER YELLOWS Host range: 200+ dicots, over 40 plant
families Vegetables, Flowers, Ornamentals, Weeds
Overwinter in dandelion, thistle
Symptoms:
Witches’ brooms, woolly 2o roots,
stunted and tapered.Bad taste!
Periwinkle:Chlorosis, dwarfing
Phylloidy: flowers develop as vegetative tissue (Horomone disruption)
Carrot
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.
Phloem
StyletEpidermis
Mesophyll
ASTER YELLOWS
Transmitted by: Grafting, budding Aster Leafhopper
CirculativePropagative
!
ELM YELLOWS (ELM PHLOEM NECROSIS)
Candidatus Phytoplasma ulmi
Symptoms:
Fine, fibrous roots die 1st
Chlorotic leaves (as roots die)
Brownish-yellow discoloration of phloem
Phloem 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)
Vector: white-banded leafhopper Circulative (persistent) -Propagative
Latent period (10-45 days) Phytoplasma must infect salivary
glands before transmission
Lay eggs in Elm bark (overwinters)
EY not transmitted to eggs
Through root grafts Phloem connections
Pollen/seed transmission unknown
EY TRANSMISSION
www.na.fs.fed.us
Nymph
Adult
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 DEDDouble-edged
sword
POINSETTIA
Native to tropical Central Am. And Mexico Introduced 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 bracts
Foliage retention
Restricted (strong apical dominance)
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 types
ELISA confirmed no virus in FB plants
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: 178-182
POINSETTIA BRANCH-INDUCING PHYTOPLASMA
Free-branching is a symptom!
Not economically detrimental
PBIP 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 Yellows
Undesirable!
FOOD FOR THOUGHT… Phytoplasma in poinsettia is desirable Color-breaking tulips
Potyvirus Are these poinsettias/tulips diseased? Are these organisms beneficial?
Symbionts or pathogens? Friend or foe?
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.