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Overexpression of Arabidopsis Fatty Acid Amide Hydrolase (FAAH) Promotes Plant Growth and Modifies Sensitivity to Exogenous N-acylethanolamines. Y.-S. Wang¹, R. Shrestha², K. D. Chapman², and E.B. Blancaflor^{1 1}Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma, ²Center for Plant Lipid Research, Department of Biological Sciences, Univ of North Texas, USA

   N-acylethanolamines (NAEs) have emerged as a group of lipid mediators involved in a wide range of animal physiological processes. One of the polyunsaturated NAEs, namely anandamide (NAE20:4), is an important component of the endocannabinoid signaling pathway that modulates a variety of physiological and behavioral processes in vertebrates. Its signaling activity within the endocannabinoid pathway is terminated by a fatty acid amide hydrolase (FAAH) that catalyzes NAEs into their corresponding free fatty acids and ethanolamines. Despite the lack of the complete endocannabinoid machinery in plants to date, several NAE types have been identified and quantified in plants. Moreover, bioinformatic approaches led to the identification of a FAAH homolog in Arabidopsis (AtFAAH; At5g64440) that is capable of hydrolyzing NAEs in vitro. We generated plants overexpressing AtFAAH to better understand the physiological role (s) of NAEs in plant development. Here we report the localization and functional characterization of the AtFAAH. An AtFAAH-GFP fusion localized to an ER-like compartment, which is consistent with its endomembrane localization in mammals. Constitutively overexpressing the AtFAAH in Arabidopsis made seedlings more tolerant to elevated levels of exogenous NAEs, which typical is inhibitory to seedling development and led to plants with significantly larger organs, partly due to increased cell size. Moreover, RT-PCR suggested constitutive AtFAAH expression in all tissues, whereas a promoter study revealed its preferential expression in rapidly elongating cells such as expanding hypocotyls cells in the dark and the elongation zone of primary roots. Taken together, we propose that overexpression of AtFAAH promotes cell enlargement/elongation, possibly through the depletion of endogenous NAEs

(Supported by DOE Biosciences grant DE-FG02-05ER15647 to KDC and EBB).