(GPB-510: Breeding for biotic and abiotic stress resistance in plants)

SIGNAL TRANSDUCTION It’s importance in plant defence

MUSHINENI ASHAJYOTHI A-2014-08-M Dept.of PlantPathology

signal

SIGNAL TRANSDUCTION It’s importance in plant defence

Significance

• Plants do not have immune system.

• Rather possess preformed and inducible defense resistance.

• These include programmed cell death, tissue reinforcement at the infection site,production of anti-microbial metabolites.

• Activation of ‘local’ responses establish secondary immunity throughout the plant (SAR), which is long lasting and effective against a broad spectrum of pathogens.

Meaning.....

• Biologically, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another.

• Signal transduction at the cellular level refers to the movement of signals.

As a defence mechanism....

• The first process in signal transduction is the perception of an extracellular signal and its transmission via the plasma membrane, resulting in accumulation of intracellular signaling molecules and induction of a phosphorylation/dephosphorylation cascade, a cue system for the activation of R gene expression.

Signal Perception

• It is a surface level phenomena in which elicitor from the pathogen are recognized by host receptor.

• Elicitors released during pathogen attack recognized by receptor of the plasma membrane.

Signal Transduction

• Perception of environmental signals, mediated by specific receptors, likely initiates internal signal pathways.

• There are two major pathways by which signal can be transduced i.e. Via protein kinases & Via G-protein.

Signal Transduction Pathways• Refers to a series of sequential events, such as

protein phosphorylations, consequent upon binding of ligand by a transmembrane receptor, that transfer a signal through a series of intermediate molecules until final regulatory molecules, such as transcription factors.

Messengers.....• Secondary messenger system exists in plants to transmit the

primary elicitation signal of pathogen and/or host.• These are:• Calcium ion influx• Protein phosphorylation• Active oxygen species• Salicylic acid• ethyl Jasmonic and Jasmonic Acid• Ethylene• Nitric Oxide

Activation of Calmodulin

• Ca2+ -important second messenger.• Include efflux of K+ ions and influx of Ca2+.• Small change in cytoplasmic Ca2+

concentrations ‘switch on’ the active form of calmodulin.

SIGNAL RESPONSES

• Massive changes in gene expression.

• In Arabidopsis more than 2000 genes changed expression levels within 9 h of inoculation with the pathogen Pseudomonas syringae (Glazebrook et al.,2003).

Agricultural applications

• Most significant payoff from this area could come in the form of strategies for engineering resistance in crops.

• Cross-species transgenic approaches might also prove useful, as overexpression of the SAR regulatory gene NPR1 in

Arabidopsis confers resistance to two different pathogens without a discernible growth penalty to the plant.

• Several promising approaches have already been initiated .

• For example, an analog of SA is being marketed as an alternative to costly and environmentally harmful fungicides.

References:

• Signal transduction in the plant immune response John M. McDowell and Jeffery L. Dangl

• Signal Transduction: Host- Pathogen Interaction PN Sharma

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