Transcript COURSE OBJECTIVES - Hebrew University of Jerusalem

COURSE OBJECTIVES: to gain knowledge about
- 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
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To sharpen written and oral communication skills
associated with research
Detailed outline of the Plant Stress course
72637 - ‫גנטיקה מולקולרית של תגובות צמחים לעקות סביבתיות‬
(14:00-‫ (שעות קבלה יום ב' מ‬86543 :‫ טל‬,2-468 ‫ד"ר אלכס לוין חדר‬
1)
2)
3)
Plant interactions with surrounding environment
Plasma membrane as the barrier and stress sensor
Oxygen and Reactive Oxygen Species in environmental stress response
(ROS chemistry, reactions, antioxidants, signaling)
Free radicals & antioxidants: Nitric oxide, oxidative stress, hypoxia
Stress signal transduction pathways:
Biochemical vs. genetic analysis and the novel genomics/functional/
comparative genomics approaches
Major regulatory signaling molecules (stress hormones, ABA, ethylene)
Intracellular messengers:
a) Ca2+ as a general and specific signaling molecule
b) Phospholipids in regulating stress signal transduction
4)
5)
5)
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)
Genetic engineering of abiotic stress resistance
7)
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Environmental stimuli that affect
plant growth
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
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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Abiotic
Water
Oxygen
Nutrients
Temperature
Salt stress
Pollutants
excess or
deficit
Biotic
Insects
Weeds
Pathogens
Plant competition
mutations
stress is the driving force behind
the process of adaptation and evolution
In biology,
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Resistance to drought and salt stresses is interlinked
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Example of elucidating stress responses
‫חץ משמעו מנגנון‬ ‫כל‬
SIGNAL TRANSDUCTION
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
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Na+ UPTAKE/EXTRUSION IN THE PLANT CELL
Plasma Membrane
PPi
Na+
K+
Na+
H+
H+
High-affinity K+
transporters
V-PPase
H+
Na+
Na+/H+ antiport
Vacuole
Na+
Na+
K+
Tonoplast
V-ATPase
K+/Na+ selectiveVICs
H+ ATP
K+/Na+ ratio
H+
ATP
P-ATPase
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Adapted from Mansour et al. 2003
ASPECTS OF SALT TOLERANCE IN PLANTS
Ionic
stress
SOS3 SOS2
Ion transporters
Ion
homeostasis
SALT STRESS
Homeostasis
Osmotic
stress
MAPK
cascade ?
Osmolytes
COLD
DROUGHT
ABA
Detoxification
Secondary
stresses
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Osmotic
homeostasis
CBF/DREB
Stress
proteins
Cell division
and expansion
Adapted from J-K Zhu 2001
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.
•
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Integration of the discovery and hypothesis approaches is area of
systems biology.
The Four Elements of Abiotic Stress
stress
Water
STRESS
Temperature
Light
time
Nutrients
in general, performance below optimal
genetic potential is indicative of stress
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Plant Responses to Stress
Mechanical concept of stress
Stress is a force per unit area
Strain 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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average losses
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).
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Crop
record
yield*
average
yield*
disease
insect
weed
other
(abiotic)
corn
19,300
4,600
750
691
511
12,700
wheat
14,500
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
10,600
1,720
465
107
352
7,960
barley
11,400
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
21.6%
4.1%
2.6%
2.6%
69.1%
% of
record
yield
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Factors that determine plant stress responses
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Strategies of stress tolerance in plants



Susceptibility
-slowed growth--senescence--death
Avoidance
-deep rooting
-short life cycle
-leaf modifications
Resistance
-ex. can survive desiccation of protoplasm
“resurrection plants”
constitutive deep roots
constitutive succulent
If plants can induce
stress resisting genes 
Why these genes are not
constitutively on?
induced freezing
toleranceresistance
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Drought avoidance
I. Important concepts of stress physiology
• 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,
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transduction, and induction
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
link between biotic and abiotic stress
signal transduction and
plant development
bon1 are miniature at 22oC
but like wild-type at 28oC
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Responses to Biotic and Abiotic stresses are
connected genetically:
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
Plant Response to Stress
• Plants adapt to changing environmental
conditions through changes in expression
patterns of numerous genes.
• 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 toxicity
by reactive oxygen 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 O2.27
Methods to study stress resistance
1.
Biochemical Approach
–
–
2.
The Genetic Approach
–
–
3.
4.
5.
6.
7.
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control vs. resistant plants
control vs. induced conditions
identify mutants with altered response
suppressor mutations
Comparative approach: complementation in yeast
The Genomic Approach
The Metabolomic Approach
The Ionomic Approach
Discovery vs. Hypothesis-Driven Science
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 forestry
HAYWARD, 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 Rubber
HAYWARD, 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
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•Disease resistance
•Yield
•Pigmentation
•Mineral nutrient use
•Biomass composition
Abiotic stress tolerance
Flowering time
Morphology
Metabolite composition
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...
Biological membranes are the primary target of many
environmental stresses. Membranes are made of
phospholipids and proteins.
~50:50 %, thus not just a barrier
phospholipid
hydrophobic
interior
phospholipid
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hydrophilic
exterior