Abstracts now available online - Euro Fed Lipid

Phospholipid and oxylipin signaling of the plant innate immune
system
Mats X Andersson*, Olga Kourtchenko*, Åsa Brunnström † , Cornelia Göbel ‡ , Ivo
Feussner ‡ , David Mackey ┼ , Mats Hamberg † and Mats Ellerström*
*Department of Botany, Göteborg University, Box 461, Sweden
†Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Sweden
‡Universität Göttingen, GZMB, Germany
┼Department of Plant Cellular and Molecular Biology, The Ohio State University, USA
Bacterial pathogens deliver type III effector proteins into the plant cell during the course
of infection. In susceptible (r) hosts, type III effectors contribute to virulence, but in the
case of resistant host-plant (R), they betray the pathogen to the plants surveillance
system. Recognition induces a complex suite of cellular and molecular events
comprising the plants inducible defense. As plant recognition of bacterial Avr proteins
occurs in the cytosol, the response can be mimicked using a transgenic system. The
gene encoding the bacterial type III effector AvrRpm1 of Pseudomonas syringae was
introduced as a chemically inducible construct in wild type (R) Arabidopsis and the rpm1
(r) mutant. Recognition of AvrRpm1 causes the sequential activation of
phosphoinositide specific phospholipase C (PLC) and phospholipase D (PLD). PLC acts
in concert with diacylglycerol kinase (DAGK) to produce phosphatidic acid (PA). The
early PLC-DAGK dependent PA production is followed by activation of PLD that
produces large amounts of PA directly from structural phospholipids. That inhibition of
either PLD or PLC inhibited response and direct feeding of PA or PLD caused
response, strongly argues for that PA is an integral part of the signaling pathway and
not just a consequence of response. We have also found that, as a consequence of
AvrRpm1 recognition, a large amount of the jasmonate 12-oxo-phytodienoic acid
(oPDA) accumulates. However, the vast majority of the oPDA is esterified to a
previously uncharacterized galactolipid. Structural determination of this novel
galactolipid (lipid X) is in progress. The accumulation of both free and esterfied oPDA
could be inhibited by inhibition of PLC or PLD, thereby establishing a link between
phospholipid signaling and oxylipins. Moreover, a mutant unable to synthesize oPDA
was clearly hampered in its defense against P. syringae. In summary, our data supports
that PA as well as oxylipins are integral and necessary components of the signal
transduction pathways of the plant innate immune system.