During III semester of Ph.D. program, I presented on a topic- Signal Transduction – Salicylic Acid Pathway. The Salicylic acid plays the role in induction of flowering, in disease resistance (HR, SAR activation). In this presentation, I have tried to explain complex pathway of salicylic acid production during the signal tranduction.

1. WELCOME

2. ENT-608
Advanced Host Plant Resistance 1+1=2
Harshvardhan Dattatraya Gaikwad
Plant Pathology (2016/49)
Topic- Signal Transduction – Salicylic Acid
Pathway

3. Signal Transduction Pathways
Transduction Pathways
CELL
WALL
CYTOPLASM
1 Reception 2 Transduction 3 Response
Receptor
Relay molecules
Activation
of cellular
responses
Hormone or
environmental
stimulus
Plasma membrane

4. • Insect, herbivory, mechanical damage, and pathogens such as bacteria
and fungi can set off a variety of peptide warning signals in plants,
which respond by increasing phytohormones, particularly Salicylic
acid (SA), jasmonic acid or jasmonate (JA), ethylene (ET), reactive
oxygen species , and nitric oxide. These mediate plant responses to
pathogen and herbivore attack.
• To survive, plants recognize and respond differently to different
attackers deploying chemical or morphological defenses that kill,
starve, poison, repel, and trap their attackers or attract the natural
enemies of these attackers.
• Some of the key endogenous chemical mediators of plant defense
signal transduction.
• Numerous genes and/or proteins have been identified that mediate
plant defense signal transduction.

5. Pathways
• Metabolic pathways are a series of chemical reactions occurring
within a cell.
• In each pathway, a principal chemical is modified by a series of
chemical reactions.
• Enzymes catalyze these reactions, and often require dietary minerals,
vitamins, and other cofactors in order to function properly.
• Numerous distinct pathways co-exist within a cell and are
compartmentalized.
• A metabolic pathway involves the step-by-step modification of an
initial molecule to form another product.
• The resulting product can be used in one of three ways:
-- To be used immediately, as the end-product of a metabolic pathway
-- To initiate another metabolic pathway, called a flux generating step
-- To be stored by the cell
• The products of one reaction are the substrates for subsequent
reactions, and so on.

6. Signal Transduction
stimulus    response
• Signal transduction is defined as the ability of a cell to change
behaviour in response to a receptor-ligand interaction.
• The ligand is the primary messenger.
• For a stimulus to elicit a response the cell must have an appropriate
receptor.
• Often a cascade of changes occur within the cell which results in a
change in the cell’s function or identity.

7. Signal Transduction Pathways
Signal transduction pathways link signal reception to
response.
Messenger molecules may be amino acids, peptides,
proteins, fatty acids, lipids, nucleosides or nucleotides.
Hydrophilic messengers bind to cell membrane receptors.
Hydrophobic messengers bind to intracellular receptors
which regulate expression of specific genes.

8. • Link cellular responses to plant hormonal signals
• Binding of a hormone to a membrane receptor
may stimulate production of secondary
messengers
• The activation of protein kinases, which in turn
activate other proteins is a common component of
signal transduction in plants
• Hormones may enter the cell to bind with a
receptor
• Environmental stimuli can also trigger signal-
transduction pathways
Signal Transduction Pathways

9. Abiotic signal
cold draught salinity
Osmotic stress
Abscisic acid
Jasmonic acid Salicylic acid
Herbivore signal Pathogen signal

10. Stimulus
Signalling molecules- Hormones, cytokine interferon, integrin , etc.
Environmental stimuli- antigens, pathogens, insects
Receptors (proteins that change in response to specific stimuli)
 On the plasma membrane, or internal
Extracellular receptors- integral transmembrane proteins, tyrosine
kinase, phosphatases
Intracelluar–receptors- nuclear receptors, cytoplasmic receptors
Secondary messengers
Calcium (Ca2+ ), G-proteins, Inositol, Phosphate, nitric oxide etc.
Effector molecules
Protein kinases or phosphatases
Transcription factors
Response
Stomatal closure
Change in growth direction
Gene activations and metabolism alterations
Signal Transduction Components

11. Reception … Transduction … Response
Reception: Internal and external signals are detected by receptors
(proteins that change in response to specific stimuli)
Transduction: Second messengers transfer and amplify signals
from receptors to proteins that cause specific responses
Response: Results in regulation of one or more cellular activities. In
many cases this involves the increased activity of certain enzymes.
CELL
WALL
CYTOPLASM
1 Reception 2 Transduction 3 Response
Receptor
Relay molecules
Activation
of cellular
responses
Hormone or
environmental
stimulus
Plasma membrane

12. Signal-transduction pathways in plants

13. STIMULUS
R
R
Ca2+
Ca2+
Kin
Phos
TF
Plasma
membrane
Nuclear
membrane
DNA
Signal transduction
Simplified model
TF-transcription factor

14. Hormones
• Brassinosteroids - growth hormone
• Salicylic acid
• Jasmonic acid stress hormones
• Oligosaccharines

15. Salicylic acid (SA)
Some roles include:
Induction of flowering
Thermogenesis regulation
Well-characterized role in disease resistance
(Hypersensitive response and Systemic Acquired
Resistance)

16. Salicylic acid (SA)

17. SA is important for local defense responses
Resistance of Arabidopsis to
Hyaloperonospora parasitica (cause of downy mildew)
Trypan blue-staining of leaves at 1, 3, 5, 7, and 9 days after infection
Blue staining indicates spread of the fungus

18. SA is also important for defense in distal parts
of the plant (systemic responses)
pick on mobile signal

19. Initial pathogen infection may increase resistance to
future pathogen attack through development of SAR

20. Methyl Salicylate Is a Critical Mobile Signal for
Plant Systemic Acquired Resistance

21. Methyl Salicylate Is a Critical Mobile Signal for
Plant Systemic Acquired Resistance

26. Figure 1. A model for SA-mediated defense networks. The networks are
grouped into three intricately interconnected sectors, SA biosynthesis, SA
accumulation and SA signaling. For SA biosynthesis, SID2 contributes to
the majority of SA production while SID2-independent pathway(s) plays
a minor role, as denoted by the thickness of the arrows. For SA
accumulation, there are multiple independent regulatory pathways. PAD4
andSAG101 physically interact with EDS1, likely acting downstream of EDS1
in two separate pathways. NDR1 is known to act independently of EDS1,
likewise, ALD1 and PAD4 function in different pathways. Expression of
many SA regulators in this group is inducible with SA treatment, suggestion
that these regulators and SA form signal amplification loops. For SA
signaling, there are both NPR1-dependent and -independent pathways.
The NPR1 node includes NIMIN proteins and transcriptions factors, such
as TGAs and WRKYs. Components in the NPR1 node can both positively
and negatively regulate plant defense. Question mark indicates that the
functional relationship of a SA regulator with other regulators is unclear.
Dotted arrow indicates the possibility that components regulating SA
accumulation may directly or indirectly affect the biosynthetic pathways.
Note not all SA regulators are shown because of space limitation.
• SID2-Dependent and SID2-Independent SA Biosynthesis
• NPR1-Dependent and NPR1-Independent Pathways Transduce SA Signaling
• SA-Mediated Defense Networks are Interconnected

27. • A localized foliar infection of plants can lead to SAR, a long lasting resistance
against a broad spectrum of pathogens at the systemic level. Gao and
coworkers summarize the importance of SA in establishing SAR in plants (Gao
et al.).
• In addition, treating plants with the SAR-related molecule diterpenoid
dehydrobietinal leads to SA accumulation in the absence of pathogen infection
(Chaturvedi et al., 2012).
• Given the critical roles of SA in plant defense and our lack of a complete
understanding of SA signaling, it is important to uncover additional genes
involved in SA-mediated defense.

30. Salicylic Acid Signaling in Plant Innate Immunity – Springer
Chapter 2
Salicylic Acid Signaling in Plant Innate Immunity
Plants are endowed with innate immune system to protect against invading
pathogens. The innate immune system serves as a surveillance system against
possible attack by viral, bacterial, fungal, and oomycete pathogens. The innate
immune system is a sleeping giant to fight against pathogens, and specific signals
are needed to activate them. The pathogen’s signature, pathogen-associated
molecular pattern (PAMP), switches on the plant innate immune system. The
PAMPs are perceived as alarm signals by plant pattern recognition receptors
(PRRs), which have a “receptor” and a “signaling domain” in one molecule to
perceive and transduce the PAMP signal. Several second messengers are involved
in delivering the message generated by the PAMP/PRR signaling complex to plant
hormone signals.
Salicylic acid (SA) is the important endogenous plant hormone signal in delivering
the extracellular PAMP message into the plant cell to initiate the transcription of
defense genes.

33. Plant defense signaling is complex

34. Thank You