M. grisea penetration

Transcription

1 Warfare between Plants and their Attacking Pathogens Presentation Outline Warfare between Plants and their Attacking Pathogens Disease Cycle Events during the infection process Inoculation comes into contact with plant Tom Hsiang ( 向培健 ) University of Guelph Ontario, Canada Part I: Infection Cycle Part II: Activating Disease Resistance fungal plant cuticle Beaumaris Castle, Wales plant epidermal cells 13 Pre-penetration water droplets Spore germination natural openings, e.g. stomate (looking for stomates) Germ tubes Plant stomates germination tube germ tube natural openings, e.g. stomates Botrytis elliptica on lily Bean rust - Uromyces appendiculatus on bean The dark, wavy, vertical line in the center is an infection tube of the rust fungus, Puccinia recondita, growing toward a stomate by Gilbert Ahlstrand. wounds s stomate = 气孔 Qìkǒng germination tubes stomatal opening specialized fungal structures for penetration such as appressoria Colletotrichum penetration from M. grisea penetration empty & appressorium penetration point (appressorium removed) Infection structures germ tube penetration peg appressorium Plant Cells germ tube penetration peg appressorium 22 Spore germ tube Spore Spore Spore germ tube 15 µm 15 µm 23 images from 24 secondary infection hyphae see figure 14 in Chen, Goodwin & Hsiang primary infection hyphae brown = fungus white = plant 25

2 peg (2 MPa, 300 psi) from Anthracnose infection process appressorium forms peg to enter plant cell from Enzymes Enzymatic digestion by hyphae similar drawing at Enzymes secreted by cells on plant surface Enzymes degrade nutrient source Nutrients are absorbed by cells peg Plant cell 26 Infection hyphae inside plant cells If you are a quadriplegic and have no teeth, how do you eat a big round ball of cheese (larger than your head)? 29 Intracellular Infection Incubation Sporulation Sporulation during the latent period (time from infection to symptom expression), the fungus incubates inside plant tissues s are produced on plant surfaces Rust s erupting Dissemination Show Infection Cycle video boths sides attack Counter attack s fly away (or vectored) to infect other tissues Scheme for the production of oligosaccharins during fungal or oomycete invasion of plant cells. Enzymes secreted by the plant, such as chitinase and glucanase, attack the fungal or oomycete wall, releasing oligosaccharins that elicit the production of defense compounds (phytoalexins) in the plant. Similarly, fungal or oomycete pectinase releases biologically active oligosaccharins from the plant cell wall. S gr1.jpg Fungal Effectors produced by fungi to increase infection may be detected by plant to block infection small proteins (30 to 300 amino acids long) secreted by fungus, taken in by plant signals on proteins (like airport luggage tags) often cysteine rich small proteins (30 to 300 amino acids long) average is > 400aa red circle fungal effectors interact with host targets that act in immunity (black shapes) red triangle fungal effectors act in self-defense to protect the pathogen from host antimicrobials

3 secreted by fungus, taken in by plant signals on proteins (like airport luggage tags) 1) secretion signal (departs YYZ) 2) uptake: RxLx (arrives LHR) often rich in cysteine (CYS) amino acid sequence complete genome of the dollar spot fungus, Sclerotinia homoeocarpa 46 million letters in the assembly search for potential effectors in the fungus > Found 38 genes that matched effector criteria created RNA libraries to look for these genes Extracted RNA daily for 0-7 days sent away for sequencing (> 2 months) 46 Summary of expression Results (reads) Protein 0 DPI 1 DPI 2 DPI 4DPI 5 DPI 6 DPI 7 DPI SH OC EF1a Future Work detect the presence of these genes in lives samples using more direct techniques attempt to figure out what these particular genes do 48 Acknowledgements Funding from the Canadian Government and the Canadian Turfgrass Research Foundation 49 How much did this cost? So far, this has cost ~$60,000=RMB 300,000 70% for personnel 20% for materials & supplies & sequencing 10% for University overhead Activating Disease Resistance in Plants Against Fungal Pathogens Plant Disease Control - fungicides Chemical control - nonselective 50 Tom Hsiang, Paul Goodwin, Ale Cortes-Barco & Brady Nash University of Guelph Beaumaris Castle, Wales New technology - activated defense Utilize a plant s natural resistance responses against abiotic stresses against insects against diseases How to break in? Physical barriers: cuticle Sneak in without being noticed

4 Sneak in without being noticed and open gates to let invaders in Or overwhelm defenders Or overwhelm defenders Internal chemical barriers Plant recognizes & responds to attacker Hypersensitive response Plant CELL kills itself (to kill invader) = hypersensitive response Plant CELL kills itself (to kill invader) Pathogen Plant cells I C U 62 Each apartment (cell) has its own set of explosives intruder (pathogen) is detected, occupant (nucleus) fights against (resists) intruder, emits calls of distress & for help (chemical signals), if it cannot defeat, it sets off explosives (autolysis) which alert & affect neighboring units (other cells) to arm themselves and prepare for battle If response too slow, invader escapes Speed of recognition and response critical to defense I C U Stimulating disease resistance response Two main forms: Systemic acquired resistance (SAR, induction) Induced systemic resistance (ISR, priming) Biological inducer or Chemical inducer Activated Resistance induction (SAR) After the signal, the soldiers in the castle are all given extra rations of caffeine to keep them awake and shooting; constant production of new arrows and boiling vats of oil... Internal (systemic) messengers Increased disease resistance Activated Resistance priming (ISR) After the signal, the cannons are loaded, the guns cocked, bows armed, fuel added under the vats of oil, and sentries on alert so action can begin as soon as enemies get close SAR ISR Resistance Activators = SAR Phosphites = ISR Aliette, Appear, SwardPhite, Magallan, Alude... Benzothiadiazole/Acibenzolar Actigard Dac Action (Daconil + Actigard) Chelated metals? Chelated iron (e.g. Fiesta) Civitas (mineral oil) + Harmonizer (chelated Cu) silicon, butanediol, humic acid... Harmonizer sprayed on Agrostis leaves, 7 d before dollar spot fungus, and rated 7 d after inoculation non- control 5% Harmonizer % % 73

5 Harmonizer applied to Agrostis roots 7 d before dollar spot fungus, and rated 7 d after inoculation non- control 5% Harmonizer October 08 dollar spot trial Agrostis stolonifera at greens height with dollarspot fungus Harmonizer+ April 2008 snow mold trials (Agrostis stolonifera at fairway height ) half rate Banner Dac/Rov untreated PCNB Inoculated Dac/Rov Harmonizer+ at different rates August 2010 dollar spot trial Agrostis at greens height, 3 wk after last treatment numbers reflect dollar spot level over entire trial Inoculated Harmonizer Untreated - outside of plot area 42 Daconil Harmonizer % % Untreated outside of plot area 77 How does Harmonizer work? Activating defenses - consequences none full too much Conclusions Direct antifungal activity? kill fungi in petri plates? Activate disease resistance in plants? make plants more resistant in lab tests? suppress disease in the field? alter gene expression in treated plants? X can reduce growth rates can slow plant development can lower crop yield stressed plants show even more negative effects can cause plant death (if too much) Think of activators like steroids (Lèigùchún) full half too much Resistance activators can provide suppression of some diseases in certain circumstances but may not work as well as conventional fungicides Their advantage greater societal and governmental acceptance with increasing restrictions» may become more important in disease management none Reprints available Cortes-Barco A, Hsiang T, Goodwin PH Induced systemic resistance against 3 foliar diseases of Agrostis stolonifera by (2R,3R)-butanediol or an isoparaffin mixture. Annals of Applied Biology 157: Hsiang T, Goodwin PH, Cortes-Barco AM Plant defense activators and control of turfgrass diseases. Outlooks Pest Management 22: Hsiang T, Goodwin PH, Cortes-Barco A, Nash B, Tung J. in press. Activating disease resistance in turfgrasses against fungal pathogens: Civitas and Harmonizer. Proceedings of PMAC 2012.