5
Conclusions
Plant responses to environmental stimuli are proportional to the intensity and the rate
of the stimulus and can occur within seconds to hours or days. The concept of
“early” is relative and depends on the dynamics of tissue and organ damage. Early
cellular responses always occur within seconds to minutes, but the resulting
responses of the signaling pathways depend on the intensity of the input perceived.
Although calcium signaling is common to various responses to environmental
stimuli, the effects of calcium on the signaling cascade and the eventual genetic
response may differ in time depending on the type of stimulus perceived. In plant
responses to biotic and abiotic environment, the term “early” is often used to indicate
the first visible or detectable effect of a stress condition. Scheme 2 summarizes some
of the biotic timing of response to biotic stimuli. The intensity and level of stress by
the biotic stressor might differ, but the downstream signaling remains somehow
similar.
In pathogenic microbes, first plant cell wall-degrading enzymes disrupt cellular
integrity. Cellular debris, ATP, and carbohydrates are sensed by DAMP that initiate
the early signaling to induce an immune response and instantly trigger signaling
from MAMP receptors that perceive conserved pathogenic proteins. In symbiotic
microbes, similar cellular damage is not sustained, and therefore, the DAMP receptors are thought to be silent and consequently repress plant immune signaling.
Concurrently, a set of mutualistic MAMP receptors also signal to repress cellular
defenses. In insect herbivore injury, the first herbivore injury causes mechanical
damage that disrupts cellular integrity and followed by the action of elicitors. Similar
to pathogenic microbes, signaling cascade cellular debris, ATP, and carbohydrates
are sensed by DAMPs that initiate the early signaling to induce an immune response
and instantly trigger signaling from HAMP receptors that perceive herbivoreassociated proteins and can also be manipulated by pathogenic effector proteins/
molecules and small interfering RNA. It is unknown whether the herbivore associated pathways in crosstalk with symbiotic or pathogenic microbes via plant miRNAs
and by mutualistic effector proteins/molecules. Neighboring plants can also rapidly
perceive root exudates and other seconder metabolites and detect these stimuli early
and trigger cascade signals (Schemes 1 and 2).
The assessment of early responses might also be dependent on the experimental
setup and the ease to quickly measure a response. It is still a matter of debate whether
early responses measured under controlled conditions, where plants can be rapidly
exposed to different environmental stimuli, will actually also occur naturally under
field conditions. Nevertheless, the ability to identify early perception of environmental stimuli can significantly improve our capability to timely detect productivity
and stress adaptation of nutritional and energy crop plants both at the local scale and
the global scale. Herbivory and other biotic stresses are quickly sensed by plants, and
timing of detection of plant responses might be crucial in rapidly changing pest and
environmental conditions.
24 Decrypting Early Perception of Biotic Stress on Plants
587
Conclusions
Plant responses to environmental stimuli are proportional to the intensity and the rate
of the stimulus and can occur within seconds to hours or days. The concept of
“early” is relative and depends on the dynamics of tissue and organ damage. Early
cellular responses always occur within seconds to minutes, but the resulting
responses of the signaling pathways depend on the intensity of the input perceived.
Although calcium signaling is common to various responses to environmental
stimuli, the effects of calcium on the signaling cascade and the eventual genetic
response may differ in time depending on the type of stimulus perceived. In plant
responses to biotic and abiotic environment, the term “early” is often used to indicate
the first visible or detectable effect of a stress condition. Scheme 2 summarizes some
of the biotic timing of response to biotic stimuli. The intensity and level of stress by
the biotic stressor might differ, but the downstream signaling remains somehow
similar.
In pathogenic microbes, first plant cell wall-degrading enzymes disrupt cellular
integrity. Cellular debris, ATP, and carbohydrates are sensed by DAMP that initiate
the early signaling to induce an immune response and instantly trigger signaling
from MAMP receptors that perceive conserved pathogenic proteins. In symbiotic
microbes, similar cellular damage is not sustained, and therefore, the DAMP receptors are thought to be silent and consequently repress plant immune signaling.
Concurrently, a set of mutualistic MAMP receptors also signal to repress cellular
defenses. In insect herbivore injury, the first herbivore injury causes mechanical
damage that disrupts cellular integrity and followed by the action of elicitors. Similar
to pathogenic microbes, signaling cascade cellular debris, ATP, and carbohydrates
are sensed by DAMPs that initiate the early signaling to induce an immune response
and instantly trigger signaling from HAMP receptors that perceive herbivoreassociated proteins and can also be manipulated by pathogenic effector proteins/
molecules and small interfering RNA. It is unknown whether the herbivore associated pathways in crosstalk with symbiotic or pathogenic microbes via plant miRNAs
and by mutualistic effector proteins/molecules. Neighboring plants can also rapidly
perceive root exudates and other seconder metabolites and detect these stimuli early
and trigger cascade signals (Schemes 1 and 2).
The assessment of early responses might also be dependent on the experimental
setup and the ease to quickly measure a response. It is still a matter of debate whether
early responses measured under controlled conditions, where plants can be rapidly
exposed to different environmental stimuli, will actually also occur naturally under
field conditions. Nevertheless, the ability to identify early perception of environmental stimuli can significantly improve our capability to timely detect productivity
and stress adaptation of nutritional and energy crop plants both at the local scale and
the global scale. Herbivory and other biotic stresses are quickly sensed by plants, and
timing of detection of plant responses might be crucial in rapidly changing pest and
environmental conditions.
24 Decrypting Early Perception of Biotic Stress on Plants
587