Abstract
BackgroundCyclopropane fatty acids (CPA) have been found in certain gymnosperms, Malvales, Litchi and other Sapindales. The presence of their unique strained ring structures confers physical and chemical properties characteristic of unsaturated fatty acids with the oxidative stability displayed by saturated fatty acids making them of considerable industrial interest. While cyclopropenoid fatty acids (CPE) are well-known inhibitors of fatty acid desaturation in animals, CPE can also inhibit the stearoyl-CoA desaturase and interfere with the maturation and reproduction of some insect species suggesting that in addition to their traditional role as storage lipids, CPE can contribute to the protection of plants from herbivory.ResultsThree 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.ConclusionsIn 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.
Highlights
Cyclopropane fatty acids (CPA) have been found in certain gymnosperms, Malvales, Litchi and other Sapindales
There are two principle classes of bacterial cyclopropane synthases: the Escherichia coli cyclopropane synthase (ECPS) type that uses unsaturated phospholipids as substrates and Mycobacterium tuberculosis cyclopropane mycolic acid synthases (CMAs) that perform the introduction of cis-cyclopropane rings at proximal and distal positions of unsaturated mycolic acids [11,12,13,14]
The cotton cyclopropane fatty acid synthase family consists of three highly conserved members A database search of the cotton genome database identified three genes predicted to encode proteins with high sequence similarity to Sterculia Cyclopropane synthases (CPSs) (Figure 1)
Summary
Cyclopropane fatty acids (CPA) have been found in certain gymnosperms, Malvales, Litchi and other Sapindales. 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 [1,2,3,4] They can represent a significant component of seed oils and accumulate to as much as 40% in Litchi chinensis [1,5]. There are two principle classes of bacterial cyclopropane synthases: the Escherichia coli cyclopropane synthase (ECPS) type that uses unsaturated phospholipids as substrates and Mycobacterium tuberculosis cyclopropane mycolic acid synthases (CMAs) that perform the introduction of cis-cyclopropane rings at proximal and distal positions of unsaturated mycolic acids [11,12,13,14] Despite their different substrates the two classes of enzymes share up to 33% sequence identity suggesting a common fold and reaction mechanism. A shared reaction mechanism is suggested by the fact that both E. coli CPS and M. tuberculosis CMA active site residues are almost completely conserved and harbor a bicarbonate ion in their active site [15,16]
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