Recently Camoni et al. [59] reported that the earliest event induced by
Spodoptera littoralis feeding on leaves is the depolarization of the Vm. Although
this herbivore-induced Vm depolarization depends on a calcium-dependent opening
of potassium channels, the attacked leaf remains depolarized for an extended period,
which cannot be explained by the sole action of potassium channels. The plasma
membrane H
+
-ATPase of Phaseolus lunatus leaves is strongly inhibited by
S. littoralis OS. Inhibition of the H
+
-ATPase was also found in plasma membranes
purified from leaf sections located distally from the application zone of OS, thus
suggesting a long-distance transport of a signaling molecule(s) [59].
OS originated elicitors includes: Fatty acid amino acid conjugate (FACs)
(volicitin, linolenic and linoleic acids coupled with either glutamine or glutamate)
[51, 54] is one of the model well studied elicitor. Though FAC-related pattern
recognition receptors (FAC-PRRs) are unknown, strikingly most of the downstream
early and late plant defense signaling is similar with MAMP/PAMP signaling. For
instance, FLS2 detects bacterial invasion by recognition and direct binding of
flagellin by bacterial flg22 epitope [12]. In Nicotiana attenuata virus-induced gene
silencing of the FLS2 co-receptor, brassinosteroid-insensitive 1 (BRI1)-associated
kinase 1 (BAK1) impairs OS-elicited JA production [60]. Silencing OS-elicited
N. attenuata CDPK4 and CDPK5 strongly increases herbivore-induced jasmonic
acid accumulations [58]. In Arabidopsis, AtCPK28 acts as a negative regulator of
PAMP-triggered immunity (PTI) signaling by phosphorylating Botrytis-induced
kinase 1 (BIK1). BIK1 is rate limiting in PTI signaling that continuously turned
over to maintain cellular homeostasis and suppressing flg22-mediated signaling
[61]. In Arabidopsis sequential interaction of FLS2, BAK1, and BIK1, the
NADPH oxidase is activated via phosphorylation resulting in increased production
of superoxide (O
2À
) and subsequent reactive oxygen species (ROS) such as H 2 O 2
[62–64]. Furthermore, oviposition by Pieris brassicae induces immune responses in
Arabidopsis that depend on the lectin-domain RLK (LecRLK) LecRLK-I.8 [52], and
the LRR-RLK BAK1 participates in anti-aphid immunity in Arabidopsis [65]. Generally, these suggest that surface-localized LRR-RLKs and/or LRR-RLPs are
involved HAMP.
4
Early Response to Neighboring Plants
Within hours, the most spectacular responses to environmental stimuli are those
aimed to optimize light harvesting under a wide variety of suboptimal conditions.
One of the most common threats to light harvesting in plants is the presence of
neighbor plants, which can intercept sunlight [66]. Plant response to the proximity of
competitors starts earlier, much before they become shaded. This depends on the
ability of plants to perceive differences in the far-red (FR) light reflected by the
leaves of the above canopy. This capability is known as the shade avoidance
response and includes rapid photochemical responses and relatively fast morphological adaptation including reduced branching, reduced biomass, increased height,
decreased leaf number, higher specific leaf area, lower chlorophyll a/b ratio,
24 Decrypting Early Perception of Biotic Stress on Plants
585
Spodoptera littoralis feeding on leaves is the depolarization of the Vm. Although
this herbivore-induced Vm depolarization depends on a calcium-dependent opening
of potassium channels, the attacked leaf remains depolarized for an extended period,
which cannot be explained by the sole action of potassium channels. The plasma
membrane H
+
-ATPase of Phaseolus lunatus leaves is strongly inhibited by
S. littoralis OS. Inhibition of the H
+
-ATPase was also found in plasma membranes
purified from leaf sections located distally from the application zone of OS, thus
suggesting a long-distance transport of a signaling molecule(s) [59].
OS originated elicitors includes: Fatty acid amino acid conjugate (FACs)
(volicitin, linolenic and linoleic acids coupled with either glutamine or glutamate)
[51, 54] is one of the model well studied elicitor. Though FAC-related pattern
recognition receptors (FAC-PRRs) are unknown, strikingly most of the downstream
early and late plant defense signaling is similar with MAMP/PAMP signaling. For
instance, FLS2 detects bacterial invasion by recognition and direct binding of
flagellin by bacterial flg22 epitope [12]. In Nicotiana attenuata virus-induced gene
silencing of the FLS2 co-receptor, brassinosteroid-insensitive 1 (BRI1)-associated
kinase 1 (BAK1) impairs OS-elicited JA production [60]. Silencing OS-elicited
N. attenuata CDPK4 and CDPK5 strongly increases herbivore-induced jasmonic
acid accumulations [58]. In Arabidopsis, AtCPK28 acts as a negative regulator of
PAMP-triggered immunity (PTI) signaling by phosphorylating Botrytis-induced
kinase 1 (BIK1). BIK1 is rate limiting in PTI signaling that continuously turned
over to maintain cellular homeostasis and suppressing flg22-mediated signaling
[61]. In Arabidopsis sequential interaction of FLS2, BAK1, and BIK1, the
NADPH oxidase is activated via phosphorylation resulting in increased production
of superoxide (O
2À
) and subsequent reactive oxygen species (ROS) such as H 2 O 2
[62–64]. Furthermore, oviposition by Pieris brassicae induces immune responses in
Arabidopsis that depend on the lectin-domain RLK (LecRLK) LecRLK-I.8 [52], and
the LRR-RLK BAK1 participates in anti-aphid immunity in Arabidopsis [65]. Generally, these suggest that surface-localized LRR-RLKs and/or LRR-RLPs are
involved HAMP.
4
Early Response to Neighboring Plants
Within hours, the most spectacular responses to environmental stimuli are those
aimed to optimize light harvesting under a wide variety of suboptimal conditions.
One of the most common threats to light harvesting in plants is the presence of
neighbor plants, which can intercept sunlight [66]. Plant response to the proximity of
competitors starts earlier, much before they become shaded. This depends on the
ability of plants to perceive differences in the far-red (FR) light reflected by the
leaves of the above canopy. This capability is known as the shade avoidance
response and includes rapid photochemical responses and relatively fast morphological adaptation including reduced branching, reduced biomass, increased height,
decreased leaf number, higher specific leaf area, lower chlorophyll a/b ratio,
24 Decrypting Early Perception of Biotic Stress on Plants
585