Stress Responses & Gene ExpressionAdaptation versus AcclimationTypes of StressSlide 4Most organisms are adapted to environmental temperature:Heat Stress (or Heat Shock) ResponseSlide 7Slide 8Cold Acclimation (CA) involves:Role of ABA (stress hormone)Plants vary in ability to tolerate floodingSlide 12Slide 13Slide 14Biotic Stress and Plant Defense ResponsesMajor PathogensPlant DefensesThe Plant Defense ResponseSlide 19Stress Responses & Gene Expression•plants must adapt to stresses because of their sedentary lifestyle Fig. 22.2, Buchanan et al.Adaptation versus Acclimation •Adaptation - evolutionary changes that enable an organism to exploit a certain niche. These include modification of existing genes, as well as gain/loss of genes.–e.g., thermo-stable enzymes in organisms that tolerate high temperature •Acclimation – inducible responses that enable an organism to tolerate an unfavorable or lethal change in their environment.–e.g., heat shock responseTypes of StressAbiotic 1. heat 2. cold 3. drought 4. salt 5. wind 6. oxidative 7. anaerobic 8. heavy metals 9. nutrient deprivation10. excessive light Biotic 1.pathogens2.herbivoresPlants respond to stresses as individual cells and as whole organisms – stress induced signals can be transmitted throughout the plant, making other parts more ready to withstand the stress.. Fig. 22.3, Buchanan et al.Most organisms are adapted to environmental temperature:1. Psychrophiles (< 20 °C)2. Mesophiles (~ 20-35 °C)3. Thermophiles ( ~35-70 °)4. Hyperthermophiles (70-110 °C) Groups 1,3 & 4 are a.k.a. “Extremophiles” But can also acclimate to “extreme” shifts, if they are not permanent, and not too extreme.Two well studied acclimation responses are:1. the Heat Shock response2. Cold acclimationHeat Stress (or Heat Shock) Response• Induced by temperatures ~10-15oC above normal • Ubiquitous (conserved), rapid & transient• Dramatic change in pattern of protein synthesis– induction (increase) of HSPs– most HSPs are chaperones (chaperonins) that promote protein re-folding & stability• HSP induction mediated by a bZIP factor, HSFFig. 22.43, Buchanan et al.28oC 40oC  45oC 45oCFig. 22.42, Buchanan et al.Soybean seedlings.Thermotolerant growth of soybean seedlings following a heat shock.Heat stress effects on protein synthesis in soybean seedlings (J. Key). Joe KeyCold Acclimation (CA) involves:•Increased accumulation of small solutes –retain water & stabilize proteins–e.g., proline, glycine betaine, trehalose •Altered membrane lipids, to lower gelling temp.•Changes in gene expression [e.g., antifreeze proteins, proteases, RNA-binding proteins (?)]•Many cold-regulated promoters have DRE/C-elements• Activated by CBF1 transcription factorRole of ABA (stress hormone)•ABA – Abscisic acid, phytohormone induced by wilting, closes stomata by acting on guard cells •Positive correlation between CA and [ABA] •Treat plants with ABA, and they will be somewhat cold hardened However, ABA does not induce all genes that cold will.Conclusion: there are ABA-regulated and non-ABA regulated changes that are induced by cold.Plants vary in ability to tolerate floodingPlants can be classified as:•Wetland plants (e.g., rice, mangroves)•Flood-tolerant (e.g., Arabidopsis, maize)•Flood-sensitive (e.g., soybeans, tomato)Involves developmental/structural, cellular and molecular adaptations.Pneumatophores in mangroveFlooding causes anoxia and an anaerobiotic response in roots.Maize (corn)Fig. 22.23- Shift carbohydrate metabolism from respiration to anaerobic glycolysis- Protein synthesis affected: results in selective synthesis of ~10-20 proteins-mRNAs for other proteins there but not translated well!Most of the ANPs are enzymes associated with glycolysis and fermentation.Fig. 22.30Protein synthesis in aerobic versus anoxic maize root tips.5-hour labeling with 3H-leucine and 2-D gel electrophoresis.Aerobic AnoxicEnzymes that are up-regulated by anaerobiosisBiotic Stress and Plant Defense Responses Pathogen Strategies1. Necrotrophic – plant tissue killed and then colonized; broad host rangee.g., rotting bacteria (Erwinia)2. Biotrophic – plant cells remain alive, narrow host range (1 plant species)e.g., viruses, nematodes, fungal mildewsMajor PathogensViruses - most are RNA viruses w/small genomes, which always encode: 1. Coat protein2. RNA-dependent RNA polymerase 3. Movement protein(s)Viroids – naked, single strands of RNA; discovered by T.O. DienerBacteria- e.g., XanthomonasFungi - 4 major groups Nematodes - root parasites, also increase infection by microorganismsds DNA virus:Cauliflower Mosaic VirusSS RNA virus: Tobacco Mosaic VirusFig. 21.10, Buchanan et al.Plant Defenses1) Physical barriers: cuticle, thorns, cell walls2) Constitutively produced chemicals (e.g., phytoalexins) and proteins (e.g., Ricin) 3) Induced responses (a.k.a., the Plant Defense Response)The Plant Defense Response3 aspects of response:1. Hypersensitive2. Local3. SystemicCompatible interaction  diseaseIncompatible interaction  resistanceDistribution of Oak Wilt in the USFungus - Ceratocystis fagacearumLeaves from Infected treeNatural root grafts Sap