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Systemic root-to-shoot defense signaling induced by arachidonic acid and extract of the brown seaweed, Ascophyllum nodosum

Richard Bostock: University of California

<div>Eicosapolyenoic fatty acids (EP) are integral components of oomycete pathogens that act as pathogen associated molecular patterns (PAMP) capable of inducing resistance in plants. EPs include arachidonic acid (AA), a robust elicitor of oxylipin pathway genes and plant defense in pepper and tomato roots. Oxylipin pathway enzymes produce antimicrobial divinyl ethers and the defense hormone jasmonic acid. A commercial extract from the seaweed <em>Ascophyllum nodosum </em>(Acadian Seaplants Ltd.; ANE) is a stimulant of plant growth that contains EPs and may also harbor the ability to induce resistance to fungal-like pathogens of Solanaceous crops similarly to AA. To investigate systemic signaling and the overlap in mechanism of action between the compounds, transcriptional analyses of oxylipin and defense marker genes were conducted. The roots of hydroponically grown tomato and pepper were treated with AA or ANE. Tissue was harvested at different times after treatment to assess local (root) and systemic (leaf) induction of target genes associated with induced resistance. Relative transcript abundance of 9- and 13-oxylipin pathway genes and jasmonate- and salicylate-inducible markers was quantified by qRT-PCR. Root treatment with either ANE or AA dramatically induced the same local and systemic transcripts. These data demonstrate that EP treatment not only protects against a root-colonizing oomycete, but also induces a systemic response in aerial tissue.</div>