1 - plant responses to environmental stress (physiological, biochemical, genetic) - research approaches for study of environmental stresses. - biochemical, genetic and molecular on one hand mechanisms responsible for environmental stress tolerance on the other hand the factors causing injury during stress. - integrate concepts from related disciplines To sharpen written and oral communication skills associated with research COURSE OBJECTIVES: to gain knowledge about
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- plant responses to environmental stress (physiological, biochemical, genetic)
- research approaches for study of environmental stresses.
- biochemical, genetic and molecular on one hand mechanisms responsible for
environmental stress tolerance on the other hand the factors causing injury
during stress.
- integrate concepts from related disciplines
To sharpen written and oral communication skills associated with research
COURSE OBJECTIVES: to gain knowledge about
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1) Plant interactions with surrounding environment 2) Plasma membrane as the barrier and stress sensor3) Oxygen and Reactive Oxygen Species in environmental stress
a) Ca2+ as a general and specific signaling moleculeb) Phospholipids in regulating stress signal transduction
chapter 18 (Trawewas:Signal Perception and Transduction) Buchanan et al, eds. (2000). Biochemistry &Molecular Biology of Plants http://www.aspb.org/downloads/BiotextCH18.pdf
6) Molecular genetics of Specific stresses: a) salt stress b) other stresses (temperature/UV/ozone/polution)
7) Genetic engineering of abiotic stress resistance
Detailed outline of the Plant Stress course
גנטיקה מולקולרית של תגובות צמחים לעקות סביבתיות - 7263714:00 (שעות קבלה יום ב' מ-86543, טל: 2-468ד"ר אלכס לוין חדר (
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Plant response to environmental stimuli
involves perception, transduction, adaptation Sensing changes in the surrounding environment
Responding to gravity and direction of light, etc.
Adjusting their growth pattern and development
Control systems in plants involve
adaptations, adaptations, adaptations
Environmental stimuli that affect plant growth
Plants need to monitor everything in order to optimize growth (i.e. to adapt) to environmental conditions, endogenous present & future
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Plants have to exploit their immediate environment to maximum effect. Their inability to move means that the best way of dealing with stress is by physiological or morphological changes.
Abiotic stresses, and ways to adapt to them are numerous and interlinked
there’s more than one way to skin a cat
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In biology, stress is the driving force behind the process of adaptation
and evolution
AbioticWaterOxygenNutrientsTemperatureSalt stressPollutants excess or
deficitBioticInsectsWeedsPathogensPlant
competition
mutations
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Resistance to drought and salt stresses is interlinked
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Example of elucidating stress responses
Inputs for ionic and osmotic signaling pathways are ionic (excess Na+) and osmotic (turgor) changes. The output of ionic and osmotic signaling is cellular and plant homeostasis. Annual Review of Plant Biology 53: 247
חץ משמעו כל SIGNAL TRANSDUCTIONמנגנון
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Na+
K+
H+
Na+
Na+
H+
H+
H+ATP
PPi
H+ATP
Tonoplast
Vacuole
Plasma Membrane
V-ATPase
P-ATPase
V-PPase
Na+/H+ antiport
K+/Na+ ratio
K+/Na+ selectiveVICs
K+
High-affinity K+ transporters
Adapted from Mansour et al. 2003
Na+ UPTAKE/EXTRUSION IN THE PLANT CELL
Na+
Na+
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ASPECTS OF SALT TOLERANCE IN PLANTS
Adapted from J-K Zhu 2001
SALT STRESS
COLDDROUGHT
ABA
Ionicstress Ion transporters
Ionhomeostasis
Osmoticstress
Secondarystresses
MAPKcascade ?
Osmolytes Osmotichomeostasis
Homeostasis
SOS3 SOS2
Stressproteins
CBF/DREB
Detoxification
Cell divisionand expansion
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Discovery vs. Hypothesis-Driven Science
• scientific projects test a hypothesis or a model that arises during
analysis of experimental data. Hypothesis is formulated and
experiments support or refute the hypothesis. While this approach
is valid, it can preclude discovery of variables, and mechanisms
that are unknown during the study design.
• An alternate approach is to nonselectively gather information
about a particular biological system; the results are then analyzed
with the hope that significant characteristics will emerge,
providing insight into the mechanism. This approach is known as
discovery science.
• Discovery science and hypothesis-driven science are
complementary approaches. Discovery science is a high
throughput method that can screen fast many genes for potential
involvement in a biological process. in contrast, Hypothesis-driven
science is low throughput method
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Discovery and Hypothesis approaches to
Science
• The Genome Projects are the first modern practice of discovery
science, now followed by other omics
• The objective of discovery science is to define all elements
in a system and to create a database containing that
information. For example, discovery approaches provide the complete
sequences & expression of the organism genes. The transcriptomes
and proteomes of all cell types
• Discovery science lies in contrast to hypothesis-driven
science, which creates hypotheses and attempts to
distinguish among them experimentally.
• Integration of the discovery and hypothesis approaches is area of
systems biology.
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The Four Elements of Abiotic Stress
STRESSSTRESS
WaterWater
LightLight
NutrientsNutrients
TemperatureTemperature
time
stre
ss
in general, performance below optimal genetic potential is
indicative of stress
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Plant Responses to Stress
Mechanical concept of stressStress is a force per unit areaStrain is a change in dimension in response to
stress (in other words, deformation of a physical body under the action of applied forces)
Failure of a material occurs when the
material cannot strain sufficiently to resist stress
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Plant Responses to Stress
Biological concept of stress Abiotic (physical or chemical) or biotic factor adversely affecting an organism Measured as effect on growth rate and
productivity
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A comparison of the record yields and the average yields indicates that mostly crops are only reaching 20% of their genetic potential due to biotic categories: disease, insect and weeds. The major reduction in yield (~ 70%) is due to abiotic stress. The most significant abiotic stress is water stress, both deficit stress (drought) and excess stress (flooding, anoxia).
average losses
Crop recor
d yield*
average
yield*
disease
insect weed other
(abiotic)
corn 19,30
0 4,600 750 691 511 12,700
wheat 14,50
0 1,880 336 134 256 11,900
soybean
7,390 1,610 269 67 330 5,120
sorghum
20,000
2,830 314 314 423 16,200
oats 10,60
0 1,720 465 107 352 7,960
barley 11,40
0 2,050 377 108 280 8,590
potatoes
94,100
28,300
8,000 5,900 875 50,900
sugar beets
121,000
42,600
6,700 6,700 3,700 61,300
% of record yield
21.6% 4.1% 2.6% 2.6% 69.1%
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Factors that determine plant stress responses
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Strategies of stress tolerance in plantsStrategies of stress tolerance in plants
constitutive succulent constitutive deep roots
Drought avoidance
induced freezingtoleranceresistance
If plants can induce stress resisting genes Why these genes are not constitutively on?
Susceptibility -slowed growth--senescence--death Avoidance -deep rooting -short life cycle -leaf modifications Resistance -ex. can survive desiccation of
protoplasm “resurrection plants”
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I. Important concepts of stress I. Important concepts of stress physiologyphysiology
• Stress– external factor that is disadvantageous to plants; survival, growth, development, yield
• Acclimated (Hardened)- increased stress tolerance as a result of prior exposure to a stress condition
• Cross Resistance- tolerance to a stress based on exposure to a previous stress event of a different nature
• Adaptation- is a genetically determined level of resistance acquired by a process of selection over many generations
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Assignment 1
• Define what are the hottest topics in plant research today– Start with general definitions, and identify the details
– Define what is already known
– Relevance to other systems and/or applicative aspects
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Responses to Environmental Stresses
• A minimum of 300 genes are required to produce a bacterial cell (based on the number of genes in Mycoplasma).
Escherichia coli contain 3000 genes. The apparently inessential 2700 (90%!) are thought necessary to provide bacteria with the ability to tolerate randomly fluctuating environmental variation
• How many genes are likely to be involved with the specification of signaling components.
• Signaling, in its broadest sense, is now the major area of plant and environmental sciences research
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I. SIGNAL TRANSDUCTION AND PLANT RESPONSES
1. Signal-transduction pathways link cellular responses to environmental stimuli
Signal transduction pathway = A mechanism linking a mechanical or chemical stimulus to a cellular response.
Three steps: reception, transduction, and induction
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Three steps: reception, transduction, and induction
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about the Signals and Signaling
• A molecule in a biological system encodes information in its shape, charge, hydrophobicity, and reactivity. Any change in a molecule’s composition encodes new information in the amount, rate, and duration of that change and where in the cell or organism the change occurs
• So, the signaling information is present in
what, where, how much and when
• note that a signal is a signal only when there is a receptor to decipher the information
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Plants respond to stress on a cellular and on the whole plant levels
growth regulation by BON1 is mediated through defense responses. BON1 is a negative regulator of a Resistance (R) gene SNC1. The bon1-1 loss-of-function mutation activates SNC1, leading to constitutive defense responses and, consequently, reduced cell growth
link between biotic and abiotic stress signal transduction and plant development
bon1 are miniature at 22oC but like wild-type at
28oC
Responses to Biotic and Abiotic stresses are connected genetically:
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• Plants adapt to changing environmental conditions through changes in expression patterns of numerous genes.
Plant Response to Stress
• There is a group of genes whose expression confers resistance to a given stress.
• There is a common core of defense genes, which responds to several different stresses (general stress-response genes) versus stress-specific genes.
• Increase in expression of protective genes is co-regulated
and is correlated with resistance to oxidative stress.
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Plants are more exposed to Plants are more exposed to toxicity by reactive oxygen toxicity by reactive oxygen species species
1) O2 availability/accessability
2) high O2 concentration
3) Multiple sources of O2.-
4) exposure to UV
5) rapid temperature shifts
6) salinity, drought
7) necrotrophic pathogens that secrete O2.-
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Methods to study stress resistance
1. Biochemical Approach– control vs. resistant plants– control vs. induced conditions
2. The Genetic Approach– identify mutants with altered response– suppressor mutations
3. Comparative approach: complementation in yeast
4. The Genomic Approach
5. The Metabolomic Approach
6. The Ionomic Approach
7. Discovery vs. Hypothesis-Driven Science
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Mendel Biotechnology was founded in 1997 to develop the idea that controlling gene
expression would improve plant growth and development. Mendel focuses on a large
class of genes called transcription factors because they control the degree to
which each gene in a cell is activated. The approximately 27,000 genes in the
Arabidopsis genome are controlled by approximately 1,800 different transcription
factors. By systematically analyzing the function of all Arabidopsis transcription
factors, Mendel scientists have discovered that single transcription factors can
control complex traits such as freezing or drought, yield, morphology, disease
resistance, nitrogen use efficiency and many other complex traits. We believe that no
other company or academic institution in the world has a comparable understanding of the
function of transcription factors and that Mendel is the leading company in the world in this
area. The company has filed a large number of patents. We believe that the inventions
described in our patent filings have placed the company in a strong position to participate
in future developments in plant biotechnology, plant breeding, horticulture, and forestry.
We are also using knowledge of plant gene expression to discover new ways of
using chemicals to control plant growth and development.
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Mendel Biotechnology Awarded SBIR Phase II Grant for Continued Research on Wide Spectrum Disease Resistance
HAYWARD, California--October 2005
Mendel's role in Monsanto trait development program highlighted in September 2005 issue of Business 2.0
HAYWARD, California--September 2005 Mendel Biotechnology and SweTree Technologies will jointly exploit the value of certain genes in forestryHAYWARD, California--October 29, 2004
Both companies announced today that they will jointly exploit the value of certain transcription factor (TF) genes within the $750 billion forestry field, among them the Hercules gene. The collaboration includes a research effort to validate certain Mendel lead TF genes for the forestry field. Mendel has demonstrated that the Hercules gene and other TF genes improve growth rate in commercial plants.
Mendel Biotechnology Awarded SBIR Phase II Grant for Continued Research to Increase Production of Natural RubberHAYWARD, California--(PRNewswire)--October 7, 2003
The Economist writes about Mendel's offer to donate drought-protection technology to the Rockefeller Foundation. -- March 27, 2003
Other Products•Disease resistance Abiotic stress tolerance •Yield Flowering time •Pigmentation Morphology •Mineral nutrient use Metabolite composition •Biomass composition
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The complexity of stress adaptation:major targets for engineered stress tolerance
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Functional genomics approach
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II. PLANT RESPONSES TO HORMONES
Hormone = A compound produced by one part of an organism that is transported to other parts where it triggers a response in target cells and tissues.
B. Plant hormones help coordinate growth, development, and responses to environmental stimuli
1) By affecting division, elongation, and differentiation of cells 2) Effects depend on site of action, stage of plant growth and hormone
concentration 3) The hormone signal is amplified, perhaps by affecting gene
expression, enzyme activity, or membrane properties 4) Reaction to hormones depends on hormonal balance 5) Five classes of plant hormones:
(1) Auxin (such as IAA).(2) Cytokinins (such as zeatin) (3) Gibberellins (such as GA3)(4) Abscisic acid (5) Ethylene
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• hormones are chemical signals that are produced in one part of the body, transported to other parts, bind to specific receptors, and trigger responses in targets cells and tissues.– Only minute quantities of hormones are necessary to induce substantial
change in an organism.
– Often the response of a plant is governed by the interaction of two or more hormones.
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Plant hormones are produced at low concentration– Signal transduction pathways amplify the hormonal signal many fold and
connect it to a cell’s specific responses.
– These include altering the expression of genes, by affecting the activity of existing enzymes, or changing the properties of membranes.
– Response to a hormone usually depends not so much on its absolute concentration as on its relative concentration compared to other hormones
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Stress physiology...Stress physiology...
Biological membranes are the primary target of many environmental stresses. Membranes are made of phospholipids and proteins.
Biological membranes are the primary target of many environmental stresses. Membranes are made of phospholipids and proteins.
