Heat shock proteins (Hsps) act as molecular chaperones that help refold or degrade proteins during stress conditions. There are five major classes of Hsps that have different functions, such as Hsp70 which helps prevent protein aggregation and refolding. Studies have shown that genetically modified plants that overexpress Hsps have enhanced tolerance to high temperatures compared to wild-type plants. Overexpressing sHsp and Hsp100 in crops improves their ability to recover after heat stress. Researchers hope that increasing Hsp levels in crops through genetic engineering can help make them more resilient to the heat stress that reduces agricultural yields worldwide.

1. HEAT SHOCK PROTEINS

2. INTRODUCTION
The molecular basis of heat shock (HS)
response was revealed for the first time
when Ritossa
(1962) reported that temperature elevation
brings about
altered puffing pattern of polytene
chromosomes in
Drosophila.

3. Tissieres et al. (1974) for the first time
showed that the HS condition results in altered
protein
profile in the Drosophila cells.
Further studies
established that nearly all organisms, ranging from
bacteria to man, respond to HS by synthesizing a
new set
of proteins called heat shock proteins (Hsp).

4. Heat shock proteins
 a class of functionally related proteins that
protect cellular proteins during stress conditions
 they act as chaperones

5. What is the role of Hsps??
ABIOTIC
STRESS
Protein dysfunction
Hsps re-establish cellular
homeostasis

6. How Hsps
work???

7. FIVE MAJOR CLASSES OF Hsps
 Hsp70 (DnaK)
 Chaperonins − Hsp60 and GroEL
 Hsp90
 Hsp100/Clp
 Small Hsp (sHsp) {under stress conditions, they may
comprise up to 1% of the cellular proteins (Agarwal et al.,
2003).}

8.  Hsp70 – prevent aggregation and help in
refolding of non native proteins.
 Hsp60 – help in protein refolding
 Hsp90 – role in signal transduction networks,
protein degradation
 Hsp100 – help in protein disaggregation or
protein degradation
 sHsps – prevent aggregation of proteins.
Functions of Hsps families

9. Hsp70, Hsp90
(signaling and
transcription
activation)
Stress
Protein
denaturation
Aggregates Degradation
Hsp100
(Resolubilizin
g)
Hsp60,Hsp70,Hs
p90(Refolding)
sHsp,Hsp70
(stabilizing &
preventing
aggregation)
Hsp network
Synthesis of
Hsp/chaperones
and other stress-
response proteins

10. Hsp/molecular
chaperone network
sHsp, Hsp60, Hsp70,
Hsp90, Hsp100 and
HSF
Signaling molecules
e.g. Hormone receptors,
kinases, cell-cycle and cell
death regulators
Regulating of redox state
Glutathione and
thioredoxin
Antioxidants
e.g. Ascorbate peroxidase
Osmolytes
e.g. Proline

11. Effects of Abiotic stress
“PRIMARY CAUSE OF CROP -LOSS WORLDWIDE”
Most crops are affected by daily fluctuations is high day and/or night
temperatures
Reduces average yields
of most major crops by
more than 50%
Grover et al. (2003) published that rDNA technology approach has great
potential in alleviating abiotic stress induced injuries
GM plants were produced which were heat stress tolerant by
manipulating HS Resistance components

12. The involvement of Hsps in regulating thermotolerance in
plants has been indicated by downregulating their levels
Mutants of Zea mays and A. thaliana plants
under-expressing their respective Hsp100 proteins are observed to lack
thermotolerance (Hong and Vierling, 2000)
Yang et al. (2006)
showed that the tomato plants silenced for Hsp100/ClpB
protein were impaired in thermotolerance.

13. Conventional breeding for high temperature stress
tolerance transgenic plants has not been much successful due to
several reasons like:
 lack of suitable source of genes in sexually compatible
gene pools
 complex nature of the HS trait
 lack of understanding on the genetic mechanisms of the
high temperature tolerance response etc
A. Singh and A.Grover (2008) Physiol. Mol. Biol. Plants; 14(1&2) : 155-166

14. UPREGULA TION OF Hsps
Genetically modified plants and cell lines were produced carrying sHsp
17.7 from carrot cell lines.
The mutant over-expressed the gene
Enhanced survival of
GM crops at high
temp.
Malik et al. 1999 Plant J. 20: 89-99

15. Expression of rice heat stress transcription factor OsHsfA2e
enhances tolerance of environmental stress in transgenic
Arabidopsis
Limited Arabidopsis growth and crop yields
Thermo-tolerance gene (OsHsfA2e) isolated from rice plants
Introduced to Arabidopsis
Transgenic Arabidopsis expresses OsHsfA2e and is
tolerant to heat stress at the cotyledon stage
Micro-array analysis showed that this gene highly expressed Hsps
In addition tolerance to high salinity stress was observed
Yokotami et al. (2007) PLANTA, Vol. 227, No. 5, pg. 957-967

16. Wild-type Arabidopsis as control
Thermo-tolerance recorded in soil grown plants
Thermo-tolerance at the vegetative
stage
Plants 4 day after heat shock
14 day-old plants were dipped into
hot water maintained at 45˚C for
10 mins.

17. Cold storage of tomatoes
specific Hsps are expressed in response
a cDNA clone hcit2 encoding a protein ca was isolated
( this gene was induced only by heat stress but expressed at low temp as well )
The expression of hcit2 gene in tomato fruits and leaves were induced at high
temp but not by other abiotic factors such as low temp etc
Preheated fruits exposed to 2° C after 2 weeks
High level of hcit2 transcript was found

18. In rice plants AtHsp100 protein was over-
expressed
The GM rice lines showed re-growth in the post-
high temp stress recovery phase while the
untransformed plants could not recover to the
similar extents
Katiyar et al. (2003)

19. References
 A. Singh and A.Grover (2008) Physiol. Mol. Biol.
Plants; 14(1&2) : 155-166
 Malik et al. 1999 Plant J. 20: 89-99
 Yokotami et al. (2007) PLANTA, Vol. 227, No. 5, pg.
957-967