1
Introduction
In plant cells, the perception of stimuli triggered by small perturbations in their
surrounding environment, and a prompt response, is mounted to prevent severe and
perhaps irreversible damage. An early response to external stimuli allows plants to
cope with stress, and the perception time ranges from seconds to minutes or hours of
exposure. Failure to rapidly perceive stimuli, transduce the signal, and regulate the
relevant genes at the appropriate time ultimately results in the inability of plant
growth and development, which eventually leads to death [1].
In plants, the concept of “early response” is related to the type and intensity of
response to external stimuli. Biotic stimuli caused by viruses, bacteria, fungi,
herbivores, and plants have different levels of intensity that correspond to different
response rates. A few hours is considered an early response time when some
responses to stimuli take days to become apparent. However, the extremely rapid
response to the rapid and intense cell and tissue damage caused by herbivores
requires response times that range from the fraction of seconds to minutes. Therefore, when defining the term “early,” we must always consider the intensity and
duration of the external stimulus.
Regardless of the type of biotic stimulus, the first general sensor is the plasma
membrane, which is considered to be the first barrier between a living cell and the
outside environment. As a dynamic system, the plasma membrane contains receptors, proteins, enzymes, transporters, and channels that all contribute to the stimulus
perception and subsequent signal transduction [1]. Second messengers have a basic
role in signal transduction, and intracellular calcium variations are involved in the
early signals of many biotic stimuli perceptions, representing a common mechanism
of the cellular response to the external environment. Tissues and organs exposed to
the environment respond specifically and sometimes differently to stimuli, allowing
the plant to make an integrated response. The timing of detection of plant responses
is important to better assess productivity, stress adaptation, natural variation, population dynamics, and plant-plant interactions in changing environmental conditions.
From this perspective, we will examine the different timing of plant responses to
biotic environmental stimuli by exploring the variability of early responses caused
by viruses, bacteria, fungi, herbivores, and nearby plants.
2
Early Perception of Stress Caused by Microorganisms
Pathogenic and beneficial microbes are initially perceived as harmful aggressors in
order to limit their invasion [2]. Early perception of pathogenic and beneficial
microbes takes place by pattern recognition receptors (PRRs) in the plant plasma
membrane. PRRs play a key role in recognizing microbe- or pathogen-associated
molecular patterns (MAMPs/PAMPs) which are microorganism molecular signatures. These molecular signatures include microbial structures, such as cell wall
components (chitin, chitin fragments (chitooligosaccharides), peptidoglycan (PNG))
and motility organs (flagellin) [3–5]. The PRRs are generally receptor-like kinases
24 Decrypting Early Perception of Biotic Stress on Plants
579
Introduction
In plant cells, the perception of stimuli triggered by small perturbations in their
surrounding environment, and a prompt response, is mounted to prevent severe and
perhaps irreversible damage. An early response to external stimuli allows plants to
cope with stress, and the perception time ranges from seconds to minutes or hours of
exposure. Failure to rapidly perceive stimuli, transduce the signal, and regulate the
relevant genes at the appropriate time ultimately results in the inability of plant
growth and development, which eventually leads to death [1].
In plants, the concept of “early response” is related to the type and intensity of
response to external stimuli. Biotic stimuli caused by viruses, bacteria, fungi,
herbivores, and plants have different levels of intensity that correspond to different
response rates. A few hours is considered an early response time when some
responses to stimuli take days to become apparent. However, the extremely rapid
response to the rapid and intense cell and tissue damage caused by herbivores
requires response times that range from the fraction of seconds to minutes. Therefore, when defining the term “early,” we must always consider the intensity and
duration of the external stimulus.
Regardless of the type of biotic stimulus, the first general sensor is the plasma
membrane, which is considered to be the first barrier between a living cell and the
outside environment. As a dynamic system, the plasma membrane contains receptors, proteins, enzymes, transporters, and channels that all contribute to the stimulus
perception and subsequent signal transduction [1]. Second messengers have a basic
role in signal transduction, and intracellular calcium variations are involved in the
early signals of many biotic stimuli perceptions, representing a common mechanism
of the cellular response to the external environment. Tissues and organs exposed to
the environment respond specifically and sometimes differently to stimuli, allowing
the plant to make an integrated response. The timing of detection of plant responses
is important to better assess productivity, stress adaptation, natural variation, population dynamics, and plant-plant interactions in changing environmental conditions.
From this perspective, we will examine the different timing of plant responses to
biotic environmental stimuli by exploring the variability of early responses caused
by viruses, bacteria, fungi, herbivores, and nearby plants.
2
Early Perception of Stress Caused by Microorganisms
Pathogenic and beneficial microbes are initially perceived as harmful aggressors in
order to limit their invasion [2]. Early perception of pathogenic and beneficial
microbes takes place by pattern recognition receptors (PRRs) in the plant plasma
membrane. PRRs play a key role in recognizing microbe- or pathogen-associated
molecular patterns (MAMPs/PAMPs) which are microorganism molecular signatures. These molecular signatures include microbial structures, such as cell wall
components (chitin, chitin fragments (chitooligosaccharides), peptidoglycan (PNG))
and motility organs (flagellin) [3–5]. The PRRs are generally receptor-like kinases
24 Decrypting Early Perception of Biotic Stress on Plants
579