Mechanism of heat stress response in plants

1. Masters seminar (MBB-591)
Mechanism of heat stress response in plants
Speaker:
Divyani Newar
MSc. 2nd year
Seminar-in-
charge:
Dr. Anupama
Singh
Assistant
Professor Department of
Biotechnology

2. • Introduction
• Plant response to heat stress
• Molecular and biotechnological assistance
• Case study
• Development of heat stress tolerance in
plants

3. INTRODUCTION
The constant rise in temperature over the years due to global warming
is a major concern in the sector of crop production.
The increasing threat of climatological extremes including very high
temperatures (Heat Stress) might lead to catastrophic loss of crop
productivity and result in widespread famine. (Bita and Gerats, 2013).
 Plant responses vary with the degree and duration of heat stress and
the plant type.
Plants possess a number of adaptive, avoidance or acclimation
mechanisms to cope with heat stress situations.
Plant survival under heat stress depends on the ability to perceive the
high temperature stimulus, generate and transmit the signal and initiate
appropriate physiological and biochemical changes.

4. Stress
Biotic
Disease ,Insects
Parasitic ,Weeds
Abiotic
Drought, cold, nutrient
salinity and heat
Heat Stress
Stress caused by high temperature which far
exceeds the temperature optimal for growth
condition of plants resulting in irreversible damage
to plant growth and development
Any external factor that
negatively impairs plant
growth, productivity,
reproductive capacity or
survival

5. EFFECTS OF HEAT STRESS ON PLANTS

6. Plant response to heat stress
1. Morpho-anatomical
and phenological
Morphological
Anatomical
Phenological
2. Physiological response
3. Molecular response
Proteins involved in heat
stress response
Regulatory pathway under
heat stress

7. The form and structure of organism
Morphological response

8. Scorching of leaves
and twigs
Sunburns on leaves,
branches and stems
Leaf senescence
Shoot and root growth
inhibition
Fruit discoloration and
damage
Reduced yield

9. Anatomical response
The internal structure of plants

10. Reduced cell size
Closure of stomata
Curtailed water loss
Increased stomatal and
trichomonas densities
Greater xylem vessels of root
and shoot

11. Phenological response
• Impairment of pollen and anther development
• Decreased fruit set
• Impairment in seed production
• During reproductive phase, increase in floral buds
and opened flower abortion
• High temperature during grain filling modify flour
and bread quality and other physico-chemical
properties, changes in protein content of flour of
grain crops such as wheat
The plant life cycle events and how these are
influenced by seasonal variation in climate

12. Inflorescence and anther cone of tomato
genotype (Bita and Gerats, 2013)

13. Example of heat-sensitive and heat-tolerant
genotypes in wheat after heat stress under field
conditions in Shanxi province China in 2017 (Geng et
al., 2018)

14. Physiological responses
• Water relations
• Accumulation of compatible osmolytes
• Photosynthesis
• Assimilate partitioning
• Cell membrane thermostability
• Hormonal changes
• Secondary metabolites
The internal activities of plants

15. PHOTOSYNTHESIS

16. Oxidative Stress
Production of ROS
 The main source of ROS production in plants and the
reaction centers of PSI andPSII is in chloroplasts, also
generated in other organelles viz mitochondria,plasma
membrane, cell wall, apoplast and peroxisomes
ROS include : O2 , O2•− , H2O • , H2O2 , OH • , RO•
organic hydroperoxide (ROOH), excited carbonyl (RO • ),
etc.
They cause damage to biomolecules like proteins, lipids,
carbohydrates, and DNA, which ultimately results in cell death

17. Reactive Oxygen Species (ROS)
• Oxidative stress is generated as a secondary
stress at times of heat stress response resulting
in the production of reactive oxygen species in
abundance.
• Chemically reactive chemical species contains
oxygen. Most common ones include singlet
oxygen (1O2), superoxide radical(O2)
hydrogen peroxide (H2O2) and hydroxyl
radical (OH) responsible for oxidative stress

20. Plant adaptation to heat
stress
Avoidance
Prevent the
exposure to stress
Tolerance
The plant is able to
grow under stress
• Closure of stomata and
reduced water loss, larger xylem
vessels, reducing the absorption
of solar radiation
• Crop management practices
such as selecting proper sowing
methods, choice of sowing date,
cultivars, irrigation methods
• Leaf orientation,
transpirational cooling and
changes in membrane lipid
composition
•Increase in antioxidative
capacity
•Osmoprotectants
•Late embryogenesis abundant
(LEA) proteins

25. TERMS
1. Heat shock transcription factor (HSF): Transcription factor
necessary for the induction of the HSR.
2. Heat stress (HS): Stress caused by temperatures far exceeding
optimal growth conditions that damages cellular components
through mechanisms such as membrane fluidization, ROS
generation, and protein denaturation.
3. Heat stress response (HSR): Physiological response to cope
with HS
4. Heat Shock Protein (HSP): HSPs are molecular chaperones
that refold and stabilize protein structures under heat stress
5. Thermotolerance: The ability to survive and continue to grow
in HS conditions
6. Chaperone: Proteins that interact with partially folded or
improperly folded polypeptides facilitating correct folding.

26. Response of ROS during heat stress

27. Role of chaperones during heat stress
• Chaperones work by binding to exposed
hydrophobic patches on misfolded or
incompletely folded proteins hydrolysing ATP
• Some of the energy expended by chaperones is
used to perform mechanical work but much more
is used to ensure the accuracy of protein folding.
• The proteins that chaperone help fold properly
are called client proteins
• There are several families of molecular
chaperones in eukaryotes which function in
different organelles one of them being Hsps

28. • Taking the example of chaperone which has a role
during heat stress is HSP 70 which itself has a set
of associated proteins
• HSPs are produced in abundance when a cell is
exposed to elevated temperatures responding to
increased amounts of misfolded proteins
• HSP 70 acts early on in the process of protein
folding binding to polypeptide chains emerging
from ribosomes
• HSP 70 is aided by HSP 40s and many cycles of
ATP hydrolysis are generally required to fold a
single polypeptide chain correctly

29. Working model of HSP 70

30. Hsf-hsp
• According to the structural features of their
oligomeric domains, plant Hsf proteins
comprise three conserved evolutionary classes:
A, B and C
• Hsf serves as the terminal component of signal
transduction and mediates the expression of
Hsp
• Hsps primarily assist in the folding and
intracellular distribution, assembly and
degradation of proteins through the
stabilization of partially unfolded proteins

31. An outline of basic function of major classes of heat
shock proteins in plant system for heat stress tolerance
Major classes of heat shock
protein
Functions
HSP 100 ATP dependent dissociation and degradation of
aggregate protein
HSP 90 Co-regulator of heat stress linked ATP dependent
signal transduction complexes and manages
protein folding
HSP 70, HSP 40 Primary stabilization of newly formed proteins, ATP
dependent binding and release
HSP 60, HSP 10 ATP dependent specialized folding machinery
HSP 20 or small HSP (sHSP) Formation of high molecular weight oligomeric
complexes which serve as cellular matrix for
stabilization of unfolded proteins. HSP 100, HSP 70
and HSP 40 are needed for its release

33. • Various signaling ions and molecules are involved in
temperature sensing and signaling
• As a signaling response to temperature stress, cytosolic
Ca2+ sharply rises likely to be linked to the acquisition
of tolerance possibly by transducing high temperature
induced signals to MAPK
• MAPK cascades are important parts of signal
transduction pathways in plants and thought to
function ubiquitously in responses to external signals

34. PHOTOSYNTHESIS RELATED
SIGNALING

35. Effects of high temperature stress in
different crop species

36. Crops Heat treatment Growth stages Major effects
Capsicum annum 30/38℃ (day/night) Reproductive, maturity
and harvesting stage
Reduced fruit width and fruit weight,
increased the proportion of
abnormal seeds/fruit
Oryza sativa Above 33℃, 10 days Heading stage Reduced the rates of pollen and
spikelet fertility
Triticum aestivum 37/28℃
(day/night), 20 days
Grain filling and
maturity stage
Shortened duration of grain filling
and maturity,
decreases in kernel weight and yield
Hordeum vulgare 40/30 °C
(day/night)
65 DAS to maturity
stage
Decreased chlorophyll content,
decreased antioxidant enzyme
activity and increased ROS content,
and reduced yield
Zea mays 35/27 °C (day/night),
14 days
Reproductive stage Reduced ear expansion, suppression
of cob extensibility by impairing
hemicellulose and cellulose synthesis
through reduction of photosynthate
supply
Abelmoschus
esculentus
32 and 34 °C Throughout the
growing period
Reduced yield, damages in pod
quality parameters such as fibre
content and break down of the Ca-
pectate.

37. Over expression of CaHsp25.9
enhances plant tolerance to heat
stress
(Feng et al., 2019)

38. • The expression pattern of the CaHsp25.9 gene in a
thermotolerant pepper line R9 and thermo-sensitive line B6
was identified.
• When silencing the CaHsp25.9 gene in the R9 line, the
accumulation of malonaldehyde (MDA), relative electrolytic
leakage, hydrogen peroxide were increased, while total
chlorophyll decreased under heat stress
• Over-expression of CaHsp25.9 in Arabidopsis resulted in
decreased MDA, while proline, superoxide dismutase
activity, germination, and root length increased under heat
stress.
• Result: CaHsp25.9 confers heat stress tolerance to plants by
reducing the accumulation of reactive oxygen species,
enhancing the activity of antioxidant enzymes, and
regulating the expression of stress-related genes.

39. Phenotype, MDA content and REL of
TRV2:00 and TRV2:CaHsp25.9 silenced
plants following heat stress at 45 °C for 16 h

40. Over-expression of the CaHsp25.9 gene
enhanced tolerance to heat stress.
Wild type (WT) and CaHsp25.9-OE Arabidopsis lines (OE2,
OE10, and OE15) at 40 °C for 16 h.

41. Development of heat tolerance
in plants

43. Proposed heat stress tolerance mechanism in plants.
Sung et al. (2003)

44. Molecular and Biotechnological
assistance

45. Two common biotechnological approaches to study and
improve plant stress tolerance include marker-assisted
selection (MAS) and genetic transformation
QTLs are promising approaches to dissect the genetic basis
of thermotolerance (Maestri et al., 2002)
Genetic engineering of heat shock factors (HSF) and
antisense strategies are instrumental to the understanding of
both the functional roles of HSPs and the regulation of HSFs.

46. Several genes responsible for inducing the synthesis of HSPs
have been identified and isolated in various plant species,
including Tomato and Maize (Liu et al., 2006)
In Arabidopsis thaliana, for example, four genomic loci
(QTLs) determining its capacity to acquire
thermotolerance were identified using a panel of heat-
sensitive mutants (Hong and Vierling, 2000).

47. Kufri Lima, a new early potato variety with superior heat tolerance,
introduced in India by CPRI and CIP (2017)
Wheat
Kaushambi (HW 2045),
Pusa Gold (WR-544), Pusa
Basant (HD-2985), Pusa
Wheat-111 (HD-2932)
Chickpea Pusa 547
Mungbean Pusa 9531
Indian mustard
Pusa Agrani (SEJ-2), Pusa
Mahak (JD-6), Pusa Vijay
(NPJ-93), Pusa Tarak (EJ-13),
Pusa Mustard-25 (NPJ-112)
High temperature tolerance varieties

48. High temperature stress has become a major concern
for crop production worldwide because it greatly
affects the growth, development, and productivity of
plants. Along with other mechanism of heat
tolerance, molecular knowledge of response and
tolerance mechanisms can pave the way for
engineering plants that can tolerate heat stress and
provide the basis for production of crops which can
produce economic yield under heat-stress conditions.