[Plant Signaling & Behavior 3:12, 1099-1100; December 2008]; ©2008 Landes Bioscience
sources for signaling messengers.6-8 Phospholipase D (PLD) hydro-
lyzes membrane phospholipids to generate phosphatidic acids (PA), a
signaling molecule involved in a variety of biological processes, such
as freezing,9 auxin and vesicular trafficking,10 root hair growth,11,12
ABA signaling in stomatal movement,13,14 and phosphorus starva-
tion.15,16 The activation of PLD and PA elevation occur in plants
under hyperosmotic stress such as dehydration17 and salt treat-
ment.18,19 However, the physiological effect of the PLD activation
and the role of specific PLDs in responses to salinity and water deficit
are largely unknown.
Plant PLD consists of a family of heterogenous enzymes.
Arabidopsis has 12 PLDs, including 10 C2-PLDs with α (3), β (2),
γ (3), δ and ε and two PH/PX-PLDζ1 and PLDζ2.20 PLDα1 is the
most abundant PLD in plants and is involved in plant water loss.
PLDα1 plays an important role in stomatal movements through
mediating ABA signaling.13,14 PLDα1-derived PA tethers ABI1 to
membrane to sequester the negative effect of ABI1 on ABA stimu-
lated stomatal closure.13 Of the three PLDs in the α group, PLDα3
is more distantly related to PLDα1 than is PLDα2. We have recently
found that PLDα3 plays a positive role in hyperosmotic stress.22
PLDα3-knockout (KO) plants are less tolerant to salt stress than
WT plants. In addition, under water deficit conditions, PLDα3-KO
plants flower later, whereas PLDα3-overexpressed (OE) plants
flower earlier than WT plants. Unlike PLDα1 that is involved in
stomatal movement through mediating ABA signaling,13,14 altera-
tion of PLDα3 does not change stomatal movement and water loss,22
suggesting that PLDα3 is involved in hyperosmotic stress response
in a mechanism different from that of PLDα1. PLDα3-KO plants
are capable of ABA accumulation induced by hyperosmotic stress.
But PLDα3-KO plants display higher levels of ABA-responsive gene
expression and ABA inhibitions on seedling growth than WT plants.
PLDα3-KO plants have fewer and shorter roots, whereas OE plants
have more and longer roots than WT plants under hyperosmotic
stress. Collectively, these results suggest that PLDα3 promotes root
growth to enhance hyperosmotic tolerance.22
Biochemical analysis shows that PLDα3 uses multiple substrates
with distinguishable preferences.22 Results of lipid profiling indi-
cate that PLDα3-KO plants accumulate less PA, suggesting that
PLDα3 contributes to PA formation under hyperosmoitc stress.22
PA has been found to be an activator of several Ser/Thr protein
kinases involved in organismal growth. In plants, PA activates PDK1
Membranes are the primary sites of perception for extracellular
stimuli and are rich sources for signaling messengers. Phospholipase
D (PLD) hydrolyzes membrane lipids to produce the messenger
phosphatidic acid (PA), and the activation of PLD occurs under
different hyperosmotic stresses, including dehydration and salt
stress. We have recently found that PLDα3 that plays a positive
role in hyperosmotic stress. PLDα3 hydrolyzes multiple substrates
with distinguishable preferences. The involvement of PLDα3 in
hyperosmotic stress is through a different mechanism from that
PLDα1, which mediates the effect of abscisic acid on stomatal
movements. PLDα3 enhances root growth and accelerates flow-
ering time under hyperosmotic stress. Alterations of PLDα3 affect
the level of PA, transcripts of TOR and AGC2.1, ABA-responsive
genes, and phosphorylated S6K protein under hyperosmotic stress.
Our further observation shows that PLDα3 is also involved in
glucose response. PLDα3-KO seeds and seedlings are less sensitive
to glucose whereas PLDα3-overepressed seeds are more sensitive
than wild type. These results point to a possibility that PLDα3-
mediated lipid signaling may play a role in integrating nutrient
sensing, protein kinase activation, and hormones responses to regu-
late growth and development under hyperosmotic stress.
Hyperosmotic stress is a critical factor that limits plant growth
and agricultural productivity. Plants experience hyperosmotic stress
under different growth conditions including high salinity and
drought. Plants have evolved to adapt various stress environments
through changes in morphological, physiological, biochemical or
molecular response.1,2 Several classes of regulatory components, such
as plant hormones, transcription factors, proteins kinases, and Ca2+
play important roles in plant response to salinity or drought signaling
processes.3-5 Increasing results show that membrane lipids are rich
*Correspondence to: Xuemin Wang; University of Missouri; Department of Biology;
R223 Research Building; One University Boulevard; St. Louis, Missouri 63121-4400
USA; Tel.: 314.516.6219; Fax: 314.516.6233; Email: firstname.lastname@example.org
Submitted: 09/05/08; Accepted: 09/16/08
Previously published online as a Plant Signaling & Behavior E-publication:
Addendum to: Hong Y, Pan X, Welti R, Wang X. Phospholipase Dα3 is involved
in the hyperosmotic response in Arabidopsis. Plant Cell 2008; 20:803–16; PMID:
18364466 ; DOI: 10.1105/tpc.107.056390.
The effect of phospholipase Dα3 on Arabidopsis response
to hyperosmotic stress and glucose
Yueyun Hong,1,2 Xiangqing Pan,1,2 Ruth Welti3 and Xuemin Wang1,2,*
1Department of Biology; University of Missouri; St. Louis, Missouri USA; 2Donald Danforth Plant Science Center; St. Louis, Missouri USA; 3Kansas Lipidomics Research Center;
Division of Biology; Kansas State University; Manhattan, Kansas USA
Key words: hyperosmotic stress, phosphatidic acid, TOR, S6K, lipid signaling, phospholipase D, glucose sensing
www.landesbioscience.comPlant Signaling & Behavior1099
The effect of phospholipase Dα3 in Arabidopsis response to hyperosmotic stress and glucose
1100 Plant Signaling & Behavior2008; Vol. 3 Issue 12
16. Cruz-Ramirez A, Oropeza-Aburto A, Razo-Hernandez F, Ramirez-Chavez E, Herrera-
Estrella L. Phospholipase DZ2 plays an important role in extraplastidic galactolipid
biosynthesis and phosphate recycling in Arabidopsis roots. Proc Natl Acad Sci USA 2006;
17. Katagiri T, Takahashi S, Shinozaki K. Involvement of a novel Arabidopsis phospholipase D,
At PLDδ, in dehydration-inducible accumulation of phosphatidic acid in stress signaling.
Plant J 2001; 26:595-605.
18. Frank W, Munnik T, Kerkmann K, Salamini F, Bartel D. Water deficit triggers phospho-
lipase D activity in the resurrection plant Craterostigma plantagineum. Plant Cell 2000;
19. Munnik T, Meijer H, Riet BT, Hirt H, Frank W, Bartels D, Musgrave A. Hyperosmotic
stress stimulates phospholipase D activity and elevates the level of phosphatidic acid and
diacylglycerol pyrophosphate. Plant J 2000; 22:147-54.
20. Qin C, Wang X. The Arabidopsis phospholipase D family. Characterization of a calcium-
independent and phosphatidylcholine-selective PLDζ1 with distinct regulatory domains.
Plant Physiol 2002; 128:1057-68.
21. Li G, Lin F, Xue HW. Genome-wide analysis of the phospholipase D family in Oryza sativa
and functional characterization of PLD beta1 in seed germination. Cell Res 2007; 17:881-94.
22. Hong Y, Pan X, Welti R, Wang X. Phospholipase Dα3 is involved in the hyperosmotic
response in Arabidopsis. Plant Cell 2008; 20:803-16; DOI: 10.1105/tpc.107.056390
23. Fang Y, Vilella-Bach M, Barchmann R, Flanigan A, Chen J. Phosphatidic acid-mediated
mitogenic activation of mTOR signaling. Science 2001; 294:1942-5.
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to phosphorylate AGC2.1 and promotes root hair growth.12 In
animals, PLD1-derived PA activates mammalian target of rapamycin
(mTOR) kinase to phosphorylate downstream kinase, ribosomal S6
kinase (S6K), PA can also directly interact with and activate S6K
to enhance cell growth.23,24 However, the linkage between PA and
TOR-S6K pathway in plants remains unknown. Further analysis
shows that KO of PLDα3 renders plants lower, whereas OE plants
have higher levels of phosphorylated S6K protein and transcripts of
TOR and AGC 2.1 than WT under hyperosmotic stress.22 These
results raise an intriguing question of whether PLDα3 is involved
in the activation of Ser/Thr protein kinases, thus regulating plants
growth and development under hyperosmotic stress.
In addition, our recent results show that alterations of PLDα3
result in changes in glucose sensitivity (Fig. 1). When seeds are
germinated in MS containing 3 and 6% glucose, PLDα3-KO seeds
and seedlings are less sensitive to glucose, as indicated by the earlier
germination and less glucose inhibition of growth, whereas OE of
PLDα3 enhances glucose sensitivity, as indicated by delayed germina-
tion and greater inhibition of seedling growth and development (Fig.
1). The effect of glucose on seed germination and seedling growth is
not due to hyperosmotic stress imposed by glucose because the effect
is opposite to that under hyperomotic stress.22 Glucose is not only a
metabolite, but also is an important signaling molecule involved in
growth, development and stress response.25 An Arabidopsis defect
in glucose sensing causes plant growth retardation.25 PLDα3 may
be involved in the crosstalk among glucose sensing, ABA response,
and S6K activation to regulate growth and development. It will be of
interest in future studies to investigate the complex network between
lipid signaling, Ser/Thr protein kinase, and nutrient sensing and
hormone response in plants.
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Figure 1. Changes in glucose sensitivity in PLDα3-KO and OE seedlings.
Seeds were germinated in MS containing 3% and 6% glucose. Values are
means ± SD (n = 3) of three experiments. Each genotype contained at least
100 seeds in each experiment.