Plastid omega3-fatty acid desaturase-dependent accumulation of a systemic acquired resistance inducing activity in petiole exudates of Arabidopsis thaliana is independent of jasmonic acid.
Systemic acquired resistance (SAR) is an inducible defense mechanism that is activated throughout the plant, subsequent to localized inoculation with a pathogen. The establishment of SAR requires translocation of an unknown signal from the pathogen-inoculated leaf to the distal organs, where salicylic acid-dependent defenses are activated. We demonstrate here that petiole exudates (PeXs) collected from Arabidopsis leaves inoculated with an avirulent (Avr) Pseudomonas syringae strain promote resistance when applied to Arabidopsis, tomato (Lycopersicum esculentum) and wheat (Triticum aestivum). Arabidopsis FATTY ACID DESATURASE7 (FAD7), SUPPRESSOR OF FATTY ACID DESATURASE DEFICIENCY1 (SFD1) and SFD2 genes are required for accumulation of the SAR-inducing activity. In contrast to Avr PeX from wild-type plants, Avr PeXs from fad7, sfd1 and sfd2 mutants were unable to activate SAR when applied to wild-type plants. However, the SAR-inducing activity was reconstituted by mixing Avr PeXs collected from fad7 and sfd1 with Avr PeX from the SAR-deficient dir1 mutant. Since FAD7, SFD1 and SFD2 are involved in plastid glycerolipid biosynthesis and SAR is also compromised in the Arabidopsis monogalactosyldiacylglycerol synthase1 mutant we suggest that a plastid glycerolipid-dependent factor is required in Avr PeX along with the DIR1-encoded lipid transfer protein for long-distance signaling in SAR. FAD7-synthesized lipids provide fatty acids for synthesis of jasmonic acid (JA). However, co-infiltration of JA and methylJA with Avr PeX from fad7 and sfd1 did not reconstitute the SAR-inducing activity. In addition, JA did not co-purify with the SAR-inducing activity confirming that JA is not the mobile signal in SAR.
Chaturvedi
Ratnesh
R
Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA.
Krothapalli
Kartikeya
K
Makandar
Ragiba
R
Nandi
Ashis
A
Sparks
Alexis A
AA
Roth
Mary R
MR
Welti
Ruth
R
Shah
Jyoti
J
D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003517:Cyclopentanes / Q000378:metabolism*; D044943:Fatty Acid Desaturases / Q000235:genetics / Q000378:metabolism; D050556:Fatty Acid-Binding Proteins; D015525:Fatty Acids, Omega-3; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005993:Glycerolphosphate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D054883:Oxylipins / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism*
D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D003517:Cyclopentanes; D050556:Fatty Acid-Binding Proteins; D015525:Fatty Acids, Omega-3; D054883:Oxylipins; C466483:dir1-1 protein, Arabidopsis; C011006:jasmonic acid; D005993:Glycerolphosphate Dehydrogenase; C487187:SFD1 protein, Arabidopsis; D044943:Fatty Acid Desaturases; C084083:Fad7 protein, Arabidopsis; C528623:SFD2 protein, Arabidopsis; C433487:stearoyl ACP desaturase, Arabidopsis; D005700:Galactosyltransferases; C109990:1,2-diacylglycerol 3-beta-galactosyltransferase; C528622:MGD1 protein, Arabidopsis