Transcript Induced Resistance

Induced Plant Resistance to
Bacteria
By Irda Safni
Materi Patogenesis Tumbuhan
1. Induced resistance to bacteria
(2 Mei 2015)
2. Phytoalexins (9 Mei 2015)
3. Effect of pathogens of plant physiology
(16 Mei 2015)  Libur
Kuliah Pengganti: ?
Introduction
Plants are central players in a complex food web
in which many members take advantages of the
plant’s resources.
Food for:
Human
Animals
Insects
Microorganisms
(fungi, bacteria, virus,
nematode, etc)
Plant faces challenges from
various herbivores &
microbes at all stages and
all organs
However, most plant are
resistant to most potential
pathogens in most times !!
Because plants have
evolved defense systems to
protect themselves!!
Plants has a good relationships with
commensal and mutualistics microbes that
provides the plants with essential services,
such as enhanced mineral uptake, nitrogen
fixation, growth promotion, and protection from
pathogens.
 These plant microbiota are predominantly
hosted by the root system  deposits up to 40% of
the plant’s photosynthetically fixed carbon into the
rhizosphere.
 Several genera of the rhizosphere microbiota,
such as plant growth–promoting rhizobacteria
(PGPR) and fungi (PGPF), can enhance plant
growth and improve health
Properties of PGPR
- Stimulate growth
• N fixation
• Increase solubility of limiting nutrients
(siderophores)
• Stimulate nutrient delivery and uptake
• Production of phytohormones
• Modulation of plant development (e.g. reduce
ethylene enhances root growth)
- Plant-mediated disease suppression
• Non-pathogens antagonize pathogens
(competition, antibiotics, lytic enzymes)
• Activating plant to better defend itself (ISR)
• Induced resistance observed on spatially
separated parts of same plant
 Some experimental studies proved evidence
that PGPR can promote plant health through
stimulation of the plant immune system.
Examples:
 The inoculation of PGPR strain Pseudomonas fluorescens
in the root system of carnation, aboveground parts of the
plant acquired an enhanced level of resistance against
infection by the fungal pathogen Fusarium oxysporum (Van
Peer et al., 1991).
 Colonization of roots by different beneficial Pseudomonas
and Serratia PGPR strains resulted in a significant reduction
in disease symptoms after challenge inoculation of leaves
with the anthracnose pathogen Colletotrichum orbiculare
(Wei et al., 1991).
Mutualism relationships between
nitrogen fixing bacteria & plants
N2 + 8H + 8e- + 16 ATP  2NH3 +H2 + 16 ADP + 16Pi
Induced Resistance
Induced resistance:
The induced state of resistance in plants
triggered by biological and chemical inducers,
which protects non-exposed plant parts against
future attacks by pathogenic microbes and
herbivorous insects.
Induced resistance can be triggered by certain
chemicals, nonpathogens, avirulent forms of
pathogens, incompatible races of pathogens or
virulent pathogen under circumstances.
 Plants can develop induced resistance as
a results of infection:
- by a pathogen or
- by a herbivorous insects, or
- after colonization of beneficial microbes, or
- after treatments with specific chemicals.
 Generally, induced resistance is systemic.
 Because of this systemic character, induced
resistance is commonly referred to as systemic
acquired resistance (SAR).
 However, induced resistance is not always
expressed systemically: Localized acquired
resistance (LAR) occurs when only those tissues
exposed to the primary invader become more
resistant.
Figure 1
Schematic representation of biologically
induced resistance triggered by pathogen
infection (red arrow),
insect herbivory (blue arrow), and
colonization of the roots by beneficial
microbes ( purple arrows).
Characteristics of induced resistance
 The activation of latent defence mechanisms.
 Induced resistance is expressed locally and
systemically (ISR).
 Induced resistance confers an enhanced level of
protection against a broad spectrum of attackers.
 Induced resistance is regulated by a network of
interconnected signaling pathways in which
plant hormones play a major regulatory role.
The Plant Immune System and Induced Resistance
What is Plant immunity?
It is a state of defense against infectious pathogens
(fungi, bacteria, virus, nematodes, etc).
Mode of entry of pathogen depend on the type of
pathogen.
 Fungi: haustoria
 Bacteria : stomata, hydatodes, and wounds
 Nematode : stylet
Gene-for-gene- Hypothesis
(by H.H. Flor)
Disease resistance in plants requires two
complementary genes: an avirulence (Avr) gene in
the pathogen and a matching, resistance (R) gene
in the host.
Principle of plant immunity
Pathogen-Induced Systemic Acquired Resistance
Signalling
Systemic Acquired Resistance (SAR):
uninfected systemic plant parts become more
resistant in response to a localized infection
elsewhere in the plant.
In the current concept of the plant immune
system, the onset of pathogen-induced SAR is
triggered upon local activation of a PTI or ETI
response.
In systemic tissues, SAR is characterized by
increased levels of the hormone salicylic
acid (SA) and pathogenesis-related proteins (PRs)..
Component & mechanism involved in ISR, HIR,SAR triggered by
beneficial microbes
 Systemic acquired resistance (SAR)
is typically activated in healthy
systemic tissues of locally infected
plants.
 Induced systemic resistance (ISR) is
typically activated upon colonization
of plant roots by beneficial
microorganisms
Hormonal Regulation of Induced Systemic
Resistance by Beneficial Microbes
Induced Systemic Resistance
 The plant hormone Jasmine Acid (JA) and Ethylene (ET) are
the central player of in the regulation of rhizobacteria-mediated
ISR.
Systemic Acquired Resistance
Several PGPR have been reported to trigger an SAdependent type of ISR that resembles pathogen induced
SAR
The Roots of Induced Systemic Resistance
Root colonization
Initiation of ISR requires beneficial microbes to
efficiently colonize the root system of host plants
For a successful mutualistic association, host
plants and microbes need to respond to reciprocal
signals and accordingly prioritize their responses so
as to develop a lifestyle that provides mutual benefits
Root colonization by beneficial soil bacteria
Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75
Plant growth-promoting effects of P. fluorescens WCS417r
Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75
Systemic protection against Cucumber mosaic virus
Nonbacterized
Bacillus pumulis strain SE34
Kloepper. 2004. Phytopathology. 94:1259-1266
Modulation of Root Immunity
Like pathogens, beneficial microbes need to
overcome or evade plant immune responses in
order to establish a prolonged and intimate
mutualistic interaction with the host.
Molecules and strategies commonly used by
pathogens to suppress host immunity are also
employed by soilborne ISR-inducing microbes.
 Many bacterial pathogens deliver immune
suppressive effectors in the plant cell via a type III
secretion system.
 Along with suppressing local host defenses to
facilitate colonization, PGPR effectors may also
function as host-range specificity determinants under
control of host resistance (R) proteins, as in the case
of the Rhizobium-legume symbiosis.
 This would allow host plants to utilize components
of their immune system to select for their mutualistic
partners.
The Rhizosphere Microbiome and Induced
Systemic Resistance
Coevolution of plant-beneficial microbe
interactions for the benefit of plant health occurs
in nature is evidenced by the existence of
disease-suppressive soils.
The disease suppressiveness of these soils is
generally based on specific microbial populations
that antagonize pathogens.
Disease-suppressive soils occur worldwide,
and some develop following prolonged
monoculture of a specific crop.
E.g. Pseudomonas (the most important player),
Trichoderma, Fusarium, Streptomyces,
Bacillus, Actinomyces spp.
Table 1. Bacterial determinants and types of systemic induced resistance
Bacterial Strain
Plant species: bacterial
determinant
Type
Pseudomonas aeruginosa :
strain 7NSK2
Tobacco: salicylic acid
SAR
Bean: salicylic acid
SAR
Tobacco: siderophore
SAR
Radish: lipopolysaccharide,
siderophore, iron-regulated factor
ISR
Carnation: lipopolysaccharide
ISR
Radish: lipopolysaccharide, ironregulated factor
ISR
Arabidopsis: lipopolysaccharide
ISR
Arabidopsis: lipopolysaccharide,
siderophore
ISR
Pseudomonas fluorescens:
CHAO
WCS417
Pseudomonas putida:
WCS358
Possible mechanisms of disease suppression:
 Competition for space and (micro)nutrients
 Hyperparasitism
 Antagosism via microbial production
of secondary metabolites, such as iron-chelating
siderophores, antibiotics, and lytic enzymes
 Elicitation of ISR
Many Pseudomonas spp. strains that have
been isolated worldwide for their excellent plant
protective properties appear to be genetically very
closely related.
Some of these closely related strains were
isolated from different plant species and thus
might embody a group of universal PGPR,
whereas others were isolated from the same plant
species and could represent plant speciesspecific beneficials.
SUMMARY POINTS
1. Beneficial microbes produce different MAMPs
and elicitors that can trigger ISR.
2. Local suppression of root immune responses is
a common feature of ISR-eliciting beneficial
microbes that possibly aids in root colonization.
3. ISR triggered by beneficial soilborne microbes
is often regulated by a JA/ET-dependent signaling
pathway, but beneficial microbes that elicit the
SA-dependent SAR pathway exist as well.
4. Plants have mechanisms by which they enrich
their microbiome with beneficial microbes that
provide protection against diseases.
5. ISR is a plant immune function mediated by the
root microbiome.
6. Disease-suppressive soils are enriched with
beneficial microbes that promote plant health.