Mosses are small avascular bryophytes with a haploid dominant gametophyte and a diploid sporophyte stage. The gametophyte cells are single layered and lack a protective cuticle, which is the first line of defense in vascular plants. These factors would render them highly susceptible to stress but on the contrary, mosses have flourished on land for the past 450 million years with tolerance to both abiotic and biotic stress. Occurrence of unique lipids in bryophytes was considered as an adaptive means to survive harsh terrestrial condition. A recent study identified a lipid metabolite, anandamide in the Physcomitrella patens. Anandamide (NAE 20:4) belongs to a group of fatty acid ethanolamides or N –acylethanolamines (NAEs). In eukaryotes, NAEs were shown to play an important role in mediating stress responses. In plants, NAE 14:0 has been implicated in biotic stress response; its levels increased up to 50-fold in elicitor-treated tobacco plants, along with induction of defense gene expression and inhibition of alkalization. In animals anandamide acts as an endocannabinoid ligand and mediates several physiological responses including stress. This study aims to use P. patens as the model system because of its available genomic database and prior studies on biotic stress, to examine if NAE 20:4 contributes to their ability to tolerate biotic stress. It is hypothesized that the occurrence of anandamide will play a role in mediating biotic stress tolerance in P. patens. To test this hypothesis, three specific aims are proposed. They are to determine the effect of 1) elicitor-treatment on NAE and fatty acid profile in the moss, 2) anandamide on elicitor-induced morphological and physiological changes in the moss and 3) anandamide on elicitor-induced defense gene expression in moss. Mosses utilize similar defense mechanisms as flowering plants and disease symptoms can easily be studied using microscopy because of their haploid dominant gametophyte stage with monolayer cells. The induction of defense gene expression will be studied by quantitative PCR and changes in lipid profile by selective lipidomics. This study is expected to provide novel insights into the role of anandamide in early land plants, specifically in response to biotic stress.