UC Davis

Eicosapolyenoic fatty acids are integral components of oomycete pathogens that can act as microbe-associated molecular patterns (MAMPs) to induce disease resistance in plants. Defense inducing eicosapolyenoic fatty acids include arachidonic (AA) and eicosapentaenoic acids, and are strong elicitors in solanaceous plants with bioactivity in other plant families. Similarly, extracts of the brown seaweed, Ascophyllum nodosum, used in sustainable agriculture as a biostimulant of plant growth, may also induce disease resistance. A. nodosum, similar to other macroalgae, is rich in eicosapolyenoic fatty acids, which comprise as much as 25% of total fatty acid composition. I investigated the response of roots and leaves from AA or a commercial A. nodosum extract (ANE) on root-treated tomatoes via RNA sequencing, phytohormone profiling, and disease assays. AA and ANE significantly altered transcriptional profiles relative to control plants, inducing numerous defense-related genes with both substantial overlap as well as differences in gene expression patterns. Root treatment with AA and, to a lesser extent, ANE also altered both salicylic acid and jasmonic acid levels while inducing local and systemic resistance to oomycete and bacterial pathogen challenge. The transcriptomic portion of this dissertation study highlights overlap in both local and systemic defense induced by AA and ANE, with potential for inducing broad-spectrum resistance against pathogens. Results of the conducted RNA sequencing analysis coupled with the shared induced resistance phenotype indicated that AA and ANE treatment may also elicit similar metabolic changes in tomato. In this dissertation work, untargeted metabolomic analysis via LCMS was conducted to investigate the local and systemic metabolome-wide remodeling events induced by AA- and ANE-root treatment. This study demonstrated AA and ANE’s capacity to locally and systemically alter the metabolome of tomato with enrichment of chemical classes and accumulation of metabolites associated with defense-related secondary metabolism. AA and ANE root-treated plants showed enrichment of fatty acyl-glycosides and strong modulation of hydroxycinnamic acids and derivatives. Identification of specific metabolites whose accumulation was affected by AA and ANE treatment revealed shared metabolic changes related to ligno-suberin biosynthesis and the synthesis of phenolic compounds. The metabolomics portion of this dissertation highlights the extensive local and systemic metabolic changes in tomato induced by treatment with a fatty acid MAMP and a seaweed-derived plant biostimulant with implications for induced resistance and crop improvement.