stress, cross talk between biotic and abiotic stresses

1. Submitted to:
DR. SHAILESH KUMAR
Assistant Professor
Dept. of Botany And Plant Physiology,
DRPCAU, PUSA

2. Introduction
Stress- anything that exert disadvantageous influence on the plants.
According to john et al 1989- “an overpowering pressure of some
adverse forces that prevent or decrease the normal system of
functioning.”
Types of stress in plant
1. Biotic stress
2. Abiotic stress

3. Biotic and abiotic stress
Biotic stress
• Insect
• Microbial pathogen- virus, fungi and bacteria
• Weeds
• Animal
Abiotic stress
Atmospheric
• Light
• Temperature
• Air pollutant
Edaphic
• Salt
• Water

4. Interaction between biotic and abiotic
When the presence of initial or previous stress alters a plant normal
responses to second stress as a result of acclimation response the
stress factor can be said to interact.
There are both positive and negative interaction depending on the
timing , nature , severity of each stress.

5. Types of interaction
Positive or additive interaction
• Abiotic stress response can be beneficial for pathogen resistance
 e.g.in barley increasing salt-induced osmotic stress was directly correlated with
resistance ton powdery mildew and while drought stress enhance resistance to
the fungus Botrytis cineria in tomato.
• Pathogens may also actively interfere with plant water relations in order to
increase pathogenesis .
e.g. They may cause stomatal closure to reduce water loss from infected tissues,
thus having positive effect on abiotic stress .
• The herbivore Spodoptera exigua showed reduced ability to feed on drought
stressed tomato eat tissue due to higher level of defence compound.

6. • Infection with virus can provide protection from drought stress
e.g. in virus infected tobacco, rice and beet, drought symptom appear later and
leaves maintained water longer than their uninfected counterparts. Metabolic
analysis suggested that it might be due to virus induced accumulation of
osmoproctectant and antioxidant such as anthocyanin.
Many type of bacteria and arbuscular mycorrhizal fungi are known to enhance
stress tolerance in many range of crop by producing antioxidant, supressing
ethylene production, stabilizing soil structure, increasing osmolyte production
and improving ABA regulation.

7. Negative interaction
• An increase in temperature can negative interactive effect by lowering resistance
to bacterial, viral, fungal and nematode pathogen.
• In wheat, it was observed that higher mean temperatures for longer period
increases susceptibility to fungus.
• The nematode and aphid resistance gene mi-1.2 is also known to be inactivated
at higher temperature more than 28 degree, promoting higher infection rate.
• Drought stress can cause detrimental effect to plant pathogen resistance.
• In both sorghum and the common bean, drought treated plant had a higher
susceptibility to the charcoal rot fungus. Similar case was observed in date palm
and Arabidopsis .

8. Physiological responses common to both biotic and abiotic stresses are
1. Level of calcium and ROS increases
2. Accumulation of phytohormones
3. Activation of defence response genes
Abiotic stress response are largely controlled by the Hormone ABA while defence against biotic stress
is specified by antagonism between Salicylic acid and Jasmonic acid/Ethylene signalling pathway.
Mechanism and controller involved in interaction
1. ABA (Abscisic acid)
ABA can act both synergistically and antagonistically with biotic stress signalling, creating a complex
network of interacting pathways with cross talk at different level.
Different cases:
• The lack of ABA can induce higher level of pathogen resistance.
• ABA treatment represses the systemic Acquired resistance pathway both upstream and downstream
of Salicylic acid induction as well as inhibiting the accumulation of crucial defence compound such
as lignin and phenylporpanoids and also Salicylic acid can also interfere with abiotic stress signalling
and increase susceptibility and supress abiotic stress resistance

9. • Resistant can be mediated by precise balanced between ABA level and S.A level
• ABA can also antagonize Jasmonic acid/Ethylene and in turn ethylene treatment
activate ABI1 and ABI2 , two negative regulator of ABA signalling
• ABA can also have positive defensive strategy of plants to prevent microbial
invasion through opening of stomata that also required SA signalling and is also
necessary for callose deposition against fungal pathogen but also inhibit callose
deposition during bacterial infection.
• The ABA inducible genes ERD-15 and ATAF1 have been identified as switches that
may activate ABA dependent biotic stress response at the expense of abiotic
response. However ABA level arising from abiotic stress may repress the SA, JA
and ethylene
Influence of ABA depends on time scale of infection and also nature of attackers .
ABA is considered as global regulator of stress responses that can dominantly
supress biotic stress defence pathways, thus controlling the switch in priority
between the response to biotic or abiotic stress allowing plant to respond in a
severe threat.

11. Transcription factor
• Transcription factors are key importance in generating specificity to stress
responses.
• MYC-2 is the central to the interaction between biotic and abiotic signal pathways
as it is positive regulator of specially JA induced defence system but repressed
gene induced by combined JA/ethylene
• it act as key repressor of SA pathway and also get activated by ABA, and myc2
mutant lack ABA responsive gene expression therefore may act as central
regulatory by which ABA control biotic stress signalling pathway.
• The MYB family of transcriptions factor is becoming increasingly associated with
the control of both biotic and abiotic stress responses, in particular in regulation
of phenylpropanoid biosynthesis pathways.
• NAC and AP2/ERF TFs have also found associated with stress signalling
• Many transcription factors confers a growth impediment when overexpressed ,
indicative of a shift in balance between allocation of resource into stress
protection rather then growth

12. MAPK(mitogen- activated protein kinases
cascade
• Plants have particularly large of no of MAPK component allowing for
control over wide range of stress response pathway.
• MAPK cascade are particularly important in controlling cross talk between
stress Reponses, as many MAPKs are activated by more than one type of
stress or plant hormone, and are thus able to integrate different signals.
• In rice least five of the identified MAPK are inducible by both biotic and
abiotic stress and certain MAPK influence both the pathway directly.
• Exposure to one stress can cause desensitization of the MAPK cascade to
another stress, a phenomenon resulting from the transient refractory state
of MAPKs after activation, underlining the similarity between responses
• MAPK cascade may be activated by and indeed regulate the production of
ROS such as H2O2 , which play a crucial role in signal cross talk.

13. HSFs(heat shocks factors)
• HSPs bind and stabilize protein that have been become denatured
during stress conditions and function as molecular chaperone which
prevent protein aggregation
• Specific combinations HSPs are included flowing different type of
abiotic stresses, and they play an important role in protecting plant
from oxidative stress
• HSPs are controlled by HSFs which may act a molecular sensor to
detect the presence of ROS and H2O2 and activate downstream stress
responsive gene accordingly.

14. Reactive oxygen species
• ROS are critical to both type of stress response , but act differently in each.
But plant have also adapted to use it as signal transduction molecule, and a
unique footprint of ROS responsive gene is induced by each type of biotic
and abiotic stress.
• H2O2 is produced by membrane bound NADPH oxidases immediately on
pathogen infection or wounding and ROS production is further more
required for ABA driven stomatal closure. ABA induces the NADPH oxidase
which generate in guard cell as signalling intermediaries.
• This commonality between biotic and abiotic stress induced ROS
production may contribute toward the positive effect of ROS on early
pathogen response, however can also have negative effect on ROS mediate
pathogen defence as demonstrated by ABA deficient sitens mutant.

15. Small Rna
• The ability of small Rna to modulate ROS regulation and controlling
gene may explain their function in both biotic and abiotic stress
pathway.
• small Rna control ROS scavenging system and it could be factor
determining the stress response of a plant.

16. Thank you

17. Reference
Nicky J.Attkinnson et al.,2012 :The interaction of plant biotic and
abiotic stresses : from gene to the field