Cold stress is one of the most common abiotic stresses which deadly effects crop security yearly. This PPT overviews the tolerance regulatory mechanisms of cold stress from physiological to the molecular levels that necessary to understand every leaners.
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Tuang Za Khai
Plant Functional Genomics,
Central China Normal University
PR China.
2. Contents
Introduction:
Major abiotic stresses
Cold stress background
How do plants perceive cold?
Cold stress and physiological responses
Cold signals sensing
(i) The cell membrane fluidity hypothesis
(ii) Calcium channels
(ii) Phytochrome
(iii) Hormone
Cold signal transduction
(i) Transcriptional regulation of ICE-CBF genes
(ii) Negative regulators of the CBF regulon
(iii) CBF-independent regulons
(iv) SA dependence transcriptional regulation
Conclusions
3. Introduction: Major abiotic stresses
◦ Cold stress: Cold stress is one of the main abiotic stress that limit crop productivity. Most template plant acquire chilling
and freezing tolerance upon their exposure to the sub-lethal cold stress, a process called cold acclimation. Cold stress effect
cellular function in plant. The cold stress signaling is transduced through several components of signal transduction
pathways, such as, Ca2+, ROS, protein kinase, protein phosphate and lipid signaling cascades as well as ABA.
◦ Salt stress: Soil salinity is another worldwide problem that seriously effect world agriculture and crop yield. Basically, salt
stress puts two effects on plant, osmotic stress and ionic toxicity. Under salt stress, the osmotic pressure in the soil solution
exceeds the osmotic pressure in plant cell due to the present of more salt, and thus, limit the ability to take up water and
minerals like K+, Ca2+, meanwhile Na+ and Cl-ion enters into the cell and have direct toxic effects on the cell membrane.
◦ Drought stress: Global climate change are leading to increases in temperature and atmospheric CO2 level as well as
disturbance in rainfall patterns. Severe drought condition brings steady decrease in soil water viability to the plant and
causes plant death although it generally effect plant growth and development.
◦ Heat stress: Heat or high temperature is also been a global concern which seriously impact plant growth and production.
Under heat stress, plant has evolved various molecular and physiological mechanism to overcome the stress.
◦ Toxin: The increase dependence of agriculture on fertilizer and sewage waste-water irrigation and rapid industrialization
has added to toxic metal to agricultural soil causing harmful effect on soil-plant environment systems.
4. Cold stress background
◦ To describe cold stress, the German plant physiologist Molisch
suggested the term ‘chilling injury’ in 1897 and later he is described as
“Hans MOLISCH: a star of plant physiology”
◦ He studied at the university of Vienna. In 1894, he became professor
in Prague and in 1909, in Vienna, he began research into "frost-
resistance" at the cellular level.
◦ Later, researchers have developed into two types of cold stress,
namely chilling and freezing.
◦ Chilling means the cold temperature above zero (ranged 2 to 6 degree
Celsius) which is required for some winter type plants such as wheat
at certain time for vernalization.
◦ Frost or freezing is minus degrees of temperature (e.g. -2 to -20 or
somehow less degree Celsius) needed for some cold tolerant / cold
hardiness winter type plants to keep themselves survive without any
damage.
Commercial Cooling of Fruits, Vegetables and Flowers (2008) Hans Molisch, Czech-Austrian botanist. (Wikipedia)
5. How do plants perceive cold?
◦ When a cell freezes, the water inside it expands as it turns to ice. This can cause the cell membrane to rupture and
lead to cell death.
◦ Plants respond to cold temperatures by activating metabolic pathways that protect their cells from cold and
freezing conditions.
◦ One protection strategy is to accumulate sugars, which decreases the temperature at which ice forms, similar to
the effect of putting salt on roads. Another is to produce proteins that stabilize membranes to help them resist
rupture.
◦ Cellular leakage of electrolytes and amino acids, a diversion of electron flow to alternate pathways (Seo et al.
2010), alterations in protoplasmic streaming and redistribution of intracellular calcium ions (Knight et al. 1998)
◦ They also involve changes in protein content and enzyme activities (Ruelland and Zachowski 2010) as well as
ultrastructural changes in a wide range of cell components, including plastids, thylakoid membranes and the
phosphorylation of thylakoid proteins, and mitochondria (Zhang et al. 2011).
6. Cold stress and physiological responses
◦ The cold signal is primarily perceived via Ca2+ channel proteins, ROS, membrane histidine kinases, membrane
rigidification or unknown sensors, which then activate the sophisticated cold-responsive signaling pathways in
concert with phytohormone signaling, and cold responsive genes or protein synthesis. Depending on this
modification, stress adaptation response or failing response will result (Kidokoro et al., 2017).
Cold stress
membrane rigidification
ROS scavenging enzymes
Ca2+
extracellular ice nucleation
(ice nuclei , ice crystal)
synthesizing protective
substances (LEA, AFP, CSP)
Failure
Response
Geneexpressions
7. Cold signals sensing
(i) The cell membrane fluidity hypothesis
Membranes are the primary site of cold-induced
injury, leading to a cascade of cellular processes with
adverse effects on the plant. When exposure to low
temperature is brief, the effects may be transitory, and
plants survive. However, the plant will exhibit
necrosis or die if exposure is maintained.
Such manner of the reduction of cell membrane
fluidity on exposure to cold stress is widely considered
to be one of cold perception mechanisms as it is the
first line of defense against cold stress.
New Phytologist (2019) 222: 1690–1704
(Lyons 1973; Raison and Lyons 1986)
8. Cold signals sensing
(ii) Calcium channels
Cytosolic Ca2+ concentration is increased very rapidly
via Ca2+ channels after cold treatment in both plants
and animals, which is considered as one of the earliest
cold signaling events (Knight & Knight, 2012).
Interestingly, cold-induced COR is dependent on Ca2+
(Knight etal., 1996). Therefore, it is possible that ion
channels (i.e. Ca2+ channels) and electrophysiological
responses mediate cold sensing in plants as well.
(iii) Phytochrome
Breakthrough studies indicated that phyB governs
photomorphogenesis under different temperatures by
perceiving light and ambient temperatures (Jung etal.,
2016; Legris et al., 2016), with phyB changing from the
active Pfr state to the inactive Pr state. phyB directly
binds to the promoters of key target genes in a
temperature-dependent manner, and phyB null mutants
exhibit a constitutive warm-temperature response (Jung
et al., 2016; Legris et al., 2016)
New Phytologist (2019) 222: 1690–1704
9. Cold signals sensing
(ii) Hormones
ABA: plays a central role in abiotic stress signaling and
its function in cold stress responses is well established.
Exogenous application of ABA promotes freezing
tolerance and ABA-controlled cold responses are
regulated by CBF independent means.
SA: contributes low temperature tolerance and
synthesis through the isochorismate synthase (ICS)
pathway. This tolerance correlated with increased
expression of CBF3, COR47 and KIN1 following cold
acclimation.
JA: like SA, JA also involved in cold stress tolerance and
synthesized from linolenic acid and is activated by
conjugation with isoleucine, which enables binding to
CORONATINE INSENSITIVE 1 (COI1). Exogenous
application of JA enhanced induction of CBFs and
CBF-regulated genes, but the induction of CORs gene
is CBFs independence manner (Hu, Jang & Wang,
2013).
Cell. Mol. Life Sci. (2016) 73: 797
Present understanding of the impact of cold stress on hormone
levels in plants. Orange arrows and blue inhibition lines
represent activation and suppression processes, respectively.
Dotted lines are used in case no or controversial data on
hormone levels were published.
10. Cold signal transduction
(i) Transcriptional regulation of ICE-CBF genes
◦ Arabidopsis contains three cold-induced CBF genes, CBF1–3 (CBF1/DREB1B,CBF2/DREB1CandCBF3/DREB1A), which
are arranged in tandem on chromosome IV.
◦ In Arabidopsis, there is another CBF gene (CBF4) that is not induced by cold; however, overexpression of CBF4 enhances plant
freezing and drought tolerance (Haake et al., 2002).
◦ ICE1 binds to the Myc recognition sequences in the CBF3 promoter.
◦ ICE1, a MYC-type bHLH transcription factor, is the best-characterized transcriptional activator of CBF genes to date
(Chinnusamy et al., 2003). ICE1 activates the expression of CBF genes by directly binding to their promoters under cold stress.
◦ ICE2, a homologue of ICE1, also plays a positive role in regulating CBF expression and freezing tolerance (Fursova et al.,
2009).
Cold
ICEs ICEs
Ca2+
inactive active
CBFs
Membrane rigidification
CORs
activeactive
Cold
acclimation
TRENDS in Plant Science
Vol.12 No.10
11. Cold signal transduction
(ii) Negative regulators of the CBF regulon
◦ CBF2 is a negative regulator of CBF1 and CBF3 expression during cold acclimation (Novillo, F. et al. (2004).
◦ Conversely, CBF3 might negatively regulate CBF2 expression (Chinnusamy, V. et al. (2003).
◦ CBFs are negatively regulated by an upstream transcription factor, MYB15. MYB15 expression decreased
expression of CBFs and a reduction in freezing tolerance (Agarwal, M. et al. (2006)
◦ ICE1 can negatively regulate MYB15 (Chinnusamy, V. et al. (2003). MYB15 can interact with ICE1, but the
functional significance of ICE1–MYB15 interaction in cold acclimation is unknown (Agarwal, M. et al.
(2006).
◦ PIF3/4/7 transcription factors, which function in light signaling, also are involved in negatively regulating
CBF expression (Jiang etal., 2017).
13. Cold signal transduction
(iii) CBF-independent regulons
◦ Only c. 10–20% of COR genes are regulated by CBFs (Zhao et al., 2016)
◦ CBFs regulate only ~12%of the cold-responsive transcriptome (Fowler, S. and Thomashow, M.F., 2002)
◦ Cold-induced transcription factor ZAT12 controls the expression of 24 COR genes (Vogel etal., 2005).
◦ BZR1 also modulates other COR genes uncoupled with CBFs, such as WRKY6, PYL6, SOC1, JMT and SAG12,
to regulate plant freezing tolerance (Li et al., 2017).
◦ WRKY33, ERF5, CZF1, RAV1, CZF2, MYB73, and HSFC1 are also cold-induced transcription factors function
in a similar manner to CBFs to induce the expression of COR genes under cold stress (Park et al., 2015).
◦ HSFA1 was found to positively regulate cold acclimation by inducing expression of heat stress-responsive genes,
which are also one type of COR genes, in a CBF-independent manner (Olate et al., 2018).
◦ HSFA1 transcription activity is activated by NPR1, a SA receptor (Ding et al., 2018)
◦ NPR1 interacts with HSFA1 in the nucleus to modulate the expression of HSFA1-regulated genes independently
of SA or TGA transcription factors (Olate et al., 2018).
15. Phytohormone dependence transcription
◦ SA is necessary for activating CBFs genes, however, overaccumulation
of SA reduce cold tolerance (Scott et al., 2004), and SA deficient NahG
and enhanced disease susceptibility (Xia et al., 2009). The expression of
NahG line and npr1‐1 mutant plants indicated that SA and NPR1 are
differentially required for the activation or inhibition of
immune‐related genes by cold stress (Wu et al., 2019).
◦ Like SA, JA also sometimes necessary for activating cold regulated
genes. JA is synthesised from linolenic acid and is activated by
conjugation with isoleucine, which enables binding to CORONATINE
INSENSITIVE 1 (COI1), an F-box protein that acts as a JA receptor.
COI1 initiates JA signalling by ubiquitinating and thereby stimulating
proteasome-dependent degradation of JASMONATE ZIM DOMAIN
(JAZ) proteins. JAZ1 and JAZ4, which physically interact with ICE1
and ICE2 to repress their transcriptional activity. JAZ4 inhibited
expression of CBFs and their downstream targets and repressed
freezing tolerance before and after cold acclimation (Hu et al., 2013).
◦ ABA also necessary for cold regulation transcription, however, ABA
dependence transcription regulation is independence to CBFs. But later
finding indicated directly or indirectly dependent to CBFs (Marina,
Wilfried & Brigitte, 2016).
ABA SA JA
RCAR/PYL COI1
MYB96
HHP2 HHP3
CAMTA ICE2
ZAJ1/4
Non CBFs
ICEs
SAR etc.
NPR1
CBFs
Cold acclimation
?
signalsignal
perception
Signaltransduction&
primaryresponse
Secondary
response
Cold
ICE1/2
16. Conclusion
◦ In summary:
◦ Hormones act as central regulators of cold stress responses in plants. However, our knowledge of their regulatory
activities remains limited and seemingly contradicting results have occasionally been published.
◦ ICE1 to CBFs regulation is well known roles in cold acclimation. The transcription represses MYB15.
◦ HOS1,9 and 10 have negatively regulate cold-induced DREB1/CBF expression.
◦ PIF3/4/7,CFPK1, MPK3/6, phyB, etc. have also negatively regulate CBFs regulation pathways
◦ The expression of CBFs is also negatively regulated by MYB15 and ZAT12.
◦ SAG12, WRKY33, ERF5, CZF1, RAV1, CZF2, MYB73, PYL6, HOS15, SOC1, JMT etc. can induce CORs genes by
CBFs independent manner.
◦ HSFC/HSFA1,2 can also regulated CORs genes by means of NPR1 in CBFs independent manner.
◦ Then, transcriptions of cold regulated genes can be dependent to phytohormone signaling pathways such as SA and
or JA.
◦ And, depend on the experiments condition, environments, methods and species, the signaling pathways or regulatory
mechanism may difference.
