Pathogen-induced systemic activation of a plant defensin gene in Arabidopsis follows a salicylic acid-independent pathway.
A 5-kD plant defensin was purified from Arabidopsis leaves challenged with the fungus Alternaria brassicicola and shown to possess antifungal properties in vitro. The corresponding plant defensin gene was induced after treatment of leaves with methyl jasmonate or ethylene but not with salicylic acid or 2,6-dichloroisonicotinic acid. When challenged with A. brassicicola, the levels of the plant defensin protein and mRNA rose both in inoculated leaves and in nontreated leaves of inoculated plants (systemic leaves). These events coincided with an increase in the endogenous jasmonic acid content of both types of leaves. Systemic pathogen-induced expression of the plant defensin gene was unaffected in Arabidopsis transformants (nahG) or mutants (npr1 and cpr1) affected in the salicylic acid response but was strongly reduced in the Arabidopsis mutants eln2 and col1 that are blocked in their response to ethylene and methyl jasmonate, respectively. Our results indicate that systemic pathogen-induced expression of the plant defensin gene in Arabidopsis is independent of salicylic acid but requires components of the ethylene and jasmonic acid response.
Penninckx
I A
IA
F. A. Janssens Laboratory of Genetics, Katholieke Universiteit Leuven, Heverlee, Belgium.
Eggermont
K
K
Terras
F R
FR
Thomma
B P
BP
De Samblanx
G W
GW
Buchala
A
A
Métraux
J P
JP
Manners
J M
JM
Broekaert
W F
WF
D000528:Alternaria / Q000472:pathogenicity*; D000595:Amino Acid Sequence; D000935:Antifungal Agents; D017360:Arabidopsis / Q000382:microbiology / Q000502:physiology*; D001483:Base Sequence; D003517:Cyclopentanes / Q000378:metabolism; D023082:Defensins; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007700:Kinetics; D008969:Molecular Sequence Data; D016296:Mutagenesis; D054883:Oxylipins; D018515:Plant Leaves; D010940:Plant Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
D000935:Antifungal Agents; D003517:Cyclopentanes; D023082:Defensins; D054883:Oxylipins; D010940:Plant Proteins; D012333:RNA, Messenger; C011006:jasmonic acid