Phospholipids Signaling System in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 378

the function of the negative regulator ABI1, thus promoting ABA signaling. It is
also shown that ABI1 is a direct target of PA and there is a functional link between
the two signaling enzymes, phospholipase and phosphatase (Zhang et al. 2004 ).
Phospholipase D (PLD) has been shown to be involved in ABA signaling-
mediated stomatal closure immune response (Uraji et al. 2012 ). Two Arabidopsis
PLDs (PLD ) are involved in ABA stomatal closure signaling in guard

cells. ABA induced stomatal closure was suppressed in the pld

α 1and PLD δ

α 1 pld δ double

mutant but not in the pld single mutants. The pld mutations reduced

ABA-induced phosphatidic acid production. During ABA-induced stomatal clo-
sure, wild-type guard cells ROS and NO and showed increased cytosolic alkaliza-
tion. These changes were reduced in guard cells of the pld

α 1 and pld δ

double mutant
plants. Inward-rectifying K + channel currents of guard cells were inhibited by ABA
in the wild-type but not in pld

α 1pld δ

mutant plants (Uraji et al. 2012 ). ABA signal-
ing system has been shown to involve ROS, NO, and phosphatidic acid, the product
of PLD activity, in Arabidopsis . PLD seems to act downstream of NO and ROS
(Distéfano et al. 2012 ). These studies suggest that ABA induces production of phos-
phatidic acid through the action of phospholipase D and the phosphatidic acid act-
ing as a second messenger triggers ROS, NO, and Ca 2+ signaling systems triggering
stomatal closure immune response.

α 1pld δ

8.7 Phosphatidic Acid in Phosphorylation/

Dephosphorylation System

PA activates a calcium-dependent protein kinase (CDPK) and a mitogen-activated
kinase (MAPK) (Munnik et al. 1995 ; Farmer and Choi 1999 ; Lee et al. 2001 ).
Together with DAG, IP3 activates protein kinase C (Munnik et al. 1995 ; Chasan
1995 ). A phosphatidic acid-activated protein kinase C isoform phosphorylates
p22 phox , an NADPH oxidase component (Regier et al. 1999 ). PA binds with ABI1
(ABA insensitive1), a protein phosphatase 2C (PP2C) that is a negative regulator of
abscisic acid (ABA) in Arabidopsis . The PA binding decreases PP2C activity and
also appears to reduce its translocation to nuclei in response to ABA by tethering
ABI1 to the plasma membrane (Zhang et al. 2004 ; Wang 2005 ; Mishra et al. 2006 ).
These results suggest that activation of PLD inhibits the function of the negative
regulator ABI1, thus promoting ABA signaling (Wang 2005 ) .

References

Alexandre J, Lassales JP, Kado RT (1990) Opening of Ca 2+ channels in isolated red beet vacuole
membrane by inositol-1,4,5-trisphosphate. Nature 343:567-570
Andersson MX, Kourtchenko O, Dangl JL, Mackey D, Ellerstrom M (2006) Phospholipase- dependent
signaling during the AvrRpm1- and AvrRpt2-induced disease resistance responses in
Arabidopsis thaliana . Plant J 47:947-959