Phospholipase‐dependent signalling during the AvrRpm1‐ and AvrRpt2‐induced disease resistance responses in Arabidopsis thaliana

Abstract

SummaryBacterial pathogens deliver type III effector proteins into plant cells during infection. On susceptible host plants, type III effectors contribute to virulence, but on resistant hosts they betray the pathogen to the plant's immune system and are functionally termed avirulence (Avr) proteins. Recognition induces a complex suite of cellular and molecular events comprising the plant's inducible defence response. As recognition of type III effector proteins occurs inside host cells, defence responses can be elicited by in planta expression of bacterial type III effectors. We demonstrate that recognition of either of two type III effectors, AvrRpm1 or AvrRpt2 from Pseudomonas syringae, induced biphasic accumulation of phosphatidic acid (PA). The first wave of PA accumulation correlated with disappearance of monophosphatidylinosotol (PIP) and is thus tentatively attributed to activation of a PIP specific phospholipase C (PLC) in concert with diacylglycerol kinase (DAGK) activity. Subsequent activation of phospholipase D (PLD) produced large amounts of PA from structural phospholipids. This later wave of PA accumulation was several orders of magnitude higher than the PLCdependent first wave. Inhibition of phospholipases blocked the response, and feeding PA directly to leaf tissue caused cell death and defence-gene activation. Inhibitor studies ordered these events relative to other known signalling events during the plant defence response. Influx of extracellular Ca 2þ occurred downstream of PIPdegradation, but upstream of PLD activation. Production of reactive oxygen species occurred downstream of the phospholipases. The data presented indicate that PA is a positive regulator of RPM1-or RPS2-mediated disease resistance signalling, and that the biphasic PA production may be a conserved feature of signalling induced by the coiled-coil nucleotide binding domain leucine-rich repeat class of resistance proteins.

SOBER1 phospholipase activity suppresses phosphatidic acid accumulation and plant immunity in response to bacterial effector AvrBsT

“…A mixture of neomycin and 1-butanol was required to inhibit HR induced by Pst DC3000 AvrRpt2 (Fig. 3 B and C and Table S1), consistent with the finding that both PLD and PLC activity contribute to RPS2-mediated disease resistance (19). These data suggest that distinct PLD isoform activity is required for AvrBsT-dependent PA accumulation and HR in Pi-0.…”

“…2) or produce HR (13). By contrast, SOBER1 did not affect AvrRpt2-elicited HR (Table S1), a response mediated by PA produced by both the PLD-and PLC-dependent pathways (19). This suggests that SOBER1 is not a general suppressor of PA-mediated immune responses during infection.…”

Synergism between elevated <i>p</i>CO<sub>2</sub> and temperature on the Antarctic sea ice diatom <i>Nitzschia lecointei</i>

“…The filters were submerged in boiling isopropanol for 5 min and dried under a stream of N 2 . Total lipids were extracted in chloroform:methanol:water (1 : 2 : 0.8, by volume) as described in Andersson et al (2006). The total lipid extract was subjected to alkaline transesterification (Christie, 1976) and analysed by gas chromatography-mass spectrometry (GC-MS) using an Agilent 7820 GC coupled to an Agilent 5975 mass selective detector.…”

Oxylipin Profiling of the Hypersensitive Response inArabidopsis thaliana

“…We are using this system to analyze the involvement of lipid-derived signal transduction processes in orchestrating the progression of the HR. We previously took advantage of this system to demonstrate the involvement of phospholipase C and D in the HR (21). In this study, the system was used to study the involvement of oxylipins in plant defense responses after recognition of P. syringae Avr proteins.…”

“…We were thus interested to test whether the recognition of AvrRpt2 also induced the accumulation of arabidopside E. To this end, we used chemically induced expression of AvrRpt2 in wild type (AvrRpt2/ Col-0) or the rps2 mutant background (AvrRpt2/rps2) (19,20). Expression of AvrRpt2 in the wild type background led to cell death but at a significantly slower rate than after expression of AvrRpm1 (21). To measure arabidopside E formation, we used [ 14 C]acetate labeling of the plant tissue before induction of AvrRpm1 and AvrRpm2 expression.…”