Characterization and analysis of the cotton cyclopropane fatty acid synthase family and their contribution to cyclopropane fatty acid synthesis

Three genes encoding cyclopropane synthase homologues GhCPS1, GhCPS2 and GhCPS3 were identified in cotton. Determination of gene transcript abundance revealed differences among the expression of GhCPS1, 2 and 3 showing high, intermediate and low levels, respectively, of transcripts in roots and stems; whereas GhCPS1 and 2 are both expressed at low levels in seeds. Analyses of fatty acid composition in different tissues indicate that the expression patterns of GhCPS1 and 2 correlate with cyclic fatty acid (CFA) distribution. Deletion of the N-terminal oxidase domain lowered GhCPS's ability to produce cyclopropane fatty acid by approximately 70%. GhCPS1 and 2, but not 3 resulted in the production of cyclopropane fatty acids upon heterologous expression in yeast, tobacco BY2 cell and Arabidopsis seed.In cotton GhCPS1 and 2 gene expression correlates with the total CFA content in roots, stems and seeds. That GhCPS1 and 2 are expressed at a similar level in seed suggests both of them can be considered potential targets for gene silencing to reduce undesirable seed CPE accumulation. Because GhCPS1 is more active in yeast than the published Sterculia CPS and shows similar activity when expressed in model plant systems, it represents a strong candidate gene for CFA accumulation via heterologous expression in production plants.Fatty acids containing three-carbon carbocyclic rings, especially cyclopropane fatty acids, occur infrequently in plants and their major plant producers include Malvaceae, Sterculiaceae, Bombaceae, Tilaceae, Gnetaceae and Sapindaceae [1-4]. They can represent a significant component of seed oils and accumulate to as much as 40% in Litchi chinensis [1,5].Cyclopropane synthases (CPSs) catalyze the cyclopropanation of unsaturated lipids in bacteria [6,7], plants [8,9] and parasites [10]. There are two principle classes of bacterial cyclopropane synthases: the Escherichia coli cyclopropane synthase (ECPS) type that uses unsaturated phospholipids as substra