Gatlin and Barrows are Chair and Vice-chair, respectively, of the Plant Products in Aquafeeds Working Group, and coordinated the development of this document; all other authors are listed in alphabetical order. AbstractContinued growth and intensi¢cation of aquaculture production depends upon the development of sustainable protein sources to replace ¢sh meal in aquafeeds. This document reviews various plant feedstu¡s, which currently are or potentially may be incorporated into aquafeeds to support the sustainable production of various ¢sh species in aquaculture. The plant feedstu¡s considered include oilseeds, legumes and cereal grains, which traditionally have been used as protein or energy concentrates as well as novel products developed through various processing technologies. The nutritional composition of these various feedstu¡s are considered along with the presence of any bioactive compounds that may positively or negatively a¡ect the target organism. Lipid composition of these feedstu¡s is not speci¢cally considered although it is recognized that incorporating lipid supplements in aquafeeds to achieve proper fatty acid pro¢les to meet the metabolic requirements of ¢sh and maximize human health bene¢ts are important aspects. Speci¢c strategies and techniques to optimize the nutritional composition of plant feedstu¡s and limit potentially adverse e¡ects of bioactive compounds are also described. Such information will provide a foundation for developing strategic research plans for increasing the use of plant feedstu¡s in aquaculture to reduce dependence of animal feedstu¡s and thereby enhance the sustainability of aquaculture.

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Specialized metabolic enzymes biosynthesize chemicals of ecological importance, often sharing a pedigree with primary metabolic enzymes1. However, the lineage of the enzyme chalcone isomerase (CHI) remained a quandary. In vascular plants, CHI-catalyzed conversion of chalcones to chiral (S)-flavanones is a committed step in the production of plant flavonoids, compounds that contribute to attraction, defense2, and development3. CHI operates near the diffusion limit with stereospecific control4,5. While associated primarily with plants, the CHI-fold occurs in several other eukaryotic lineages and in some bacteria. Here we report crystal structures, ligand-binding properties, and in vivo functional characterization of a non-catalytic CHI-fold family from plants. A. thaliana contains five actively transcribed CHI-fold genes, three of which additionally encode amino-terminal chloroplast-transit sequences (cTP). These three CHI-fold proteins localize to plastids, the site of de novo fatty acid (FA) biosynthesis in plant cells. Furthermore, their expression profiles correlate with those of core FA biosynthetic enzymes, with maximal expression occurring in seeds and coinciding with increased FA storage in the developing embryo. In vitro, these proteins are Fatty Acid-binding Proteins (FAP). FAP knockout A. thaliana plants exhibit elevated alpha-linolenic acid levels and marked reproductive defects, including aberrant seed formation. Notably, the FAP discovery defines the adaptive evolution of a stereospecific and catalytically ‘perfected’ enzyme6 from a non-enzymatic ancestor over a defined period of plant evolution.

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