The tomato suppressor of prosystemin-mediated responses2 gene encodes a fatty acid desaturase required for the biosynthesis of jasmonic acid and the production of a systemic wound signal for defense gene expression.
Genetic analysis of the wound response pathway in tomato indicates that systemin and its precursor protein, prosystemin, are upstream components of a defensive signaling cascade that involves the synthesis and subsequent action of the octadecatrienoic acid (18:3)-derived plant hormone jasmonic acid (JA). The suppressor of prosystemin-mediated responses2 (spr2) mutation, which was isolated previously as a suppressor of (pro)systemin-mediated signaling, impairs wound-induced JA biosynthesis and the production of a long-distance signal for the expression of defensive Proteinase inhibitor genes. Using a map-based cloning approach, we demonstrate here that Spr2 encodes a chloroplast fatty acid desaturase involved in JA biosynthesis. Loss of Spr2 function reduced the 18:3 content of leaves to <10% of wild-type levels, abolished the accumulation of hexadecatrienoic acid, and caused a corresponding increase in the level of dienoic fatty acids. The effect of spr2 on the fatty acyl content of various classes of glycerolipids indicated that the Spr2 gene product catalyzes most, if not all, omega3 fatty acid desaturation within the "prokaryotic pathway" for lipid synthesis in tomato leaves. Despite the reduced levels of trienoic fatty acids, spr2 plants exhibited normal growth, development, and reproduction. However, the mutant was compromised in defense against attack by tobacco hornworm larvae. These results indicate that jasmonate synthesis from chloroplast pools of 18:3 is required for wound- and systemin-induced defense responses and support a role for systemin in the production of a transmissible signal that is derived from the octadecanoid pathway.
Li
Chuanyou
C
Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
Liu
Guanghui
G
Xu
Changcheng
C
Lee
Gyu In
GI
Bauer
Petra
P
Ling
Hong-Qing
HQ
Ganal
Martin W
MW
Howe
Gregg A
GA
D000818:Animals; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D003517:Cyclopentanes / Q000378:metabolism*; D044943:Fatty Acid Desaturases / Q000235:genetics* / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007113:Immunity, Innate / Q000235:genetics; D007313:Insecta / Q000254:growth & development; D007814:Larva / Q000254:growth & development; D018551:Solanum lycopersicum / Q000235:genetics* / Q000378:metabolism / Q000469:parasitology; D008969:Molecular Sequence Data; D054883:Oxylipins; D010455:Peptides / Q000378:metabolism; D010641:Phenotype; D010802:Phylogeny; D010935:Plant Diseases / Q000469:parasitology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D013314:Stress, Mechanical
D003517:Cyclopentanes; D005231:Fatty Acids, Unsaturated; D054883:Oxylipins; D010455:Peptides; D010940:Plant Proteins; C034104:proteinase inhibitor II protein, plant; C073705:prosystemin protein, Lycopersicon esculentum; C073704:systemin; C011006:jasmonic acid; D044943:Fatty Acid Desaturases; C078565:omega-3 fatty acid desaturase