Characterization of the Fatty Acid Desaturase Genes in Cucumber: Structure, Phylogeny, and Expression Patterns

Abstract

Fatty acid desaturases (FADs) introduce double bonds into the hydrocarbon chains of fatty acids to produce unsaturated fatty acids, and therefore play a critical role in plant development and acclimation to environmental stresses. In this study, 23 full-length FAD genes in cucumber (Cucumis sativus L.) were identified through database searches, including three CsFAB2 genes, two CsFAD2 genes, fourteen CsFAD5 genes, and one gene each for CsFAD3, CsFAD4, CsFAD6 and CsFAD7. These cucumber FAD genes were distributed on all seven chromosomes and two additional scaffolds. Based on a phylogenetic analysis, the cucumber FAD proteins were clustered into five subfamilies with their counterparts from other plants. Gene structures and protein sequences were considerably conserved in each subfamily. All three CsFAB2 proteins shared conserved structure with the known plant soluble FAD proteins. The other cucumber FADs belonged to the membrane-bound FADs and contained three highly conserved histidine boxes. Additionally, the putative endoplasmic reticulum retention signal was found at the C-termini of the CsFAD2 and CsFAD3 proteins, while the N-termini of CsFAD4, CsFAD5, CsFAD6, CsFAD7 and three CsFAB2s contained a predicted chloroplast signal peptide, which was consistent with their associated metabolic pathways. Furthermore, a gene expression analysis showed that CsFAD2 and CsFAD3 were universally expressed in all tested tissues, whereas the other cucumber FAD genes were preferentially expressed in the cotyledons or leaves. The tissue-specific expression patterns of cucumber FAD genes were correlated well with the differences in the fatty acid compositions ofroots and leaves. Finally, the cucumber FAD genes showed a cold-induced and heat-repressed expression pattern, although with distinct regulatory time courses among the different CsFAD members, which indicates the potential roles of the FADs in temperature stress resistance in cucumber.

Apple fruit superficial scald resistance mediated by ethylene inhibition is associated with diverse metabolic processes

“…In general, another mechanism that is employed in the fruit to repair damages induced by cold stress is the activation of FAD expression. FAD proteins catalyze the insertion of double bonds into the hydrocarbon chain of fatty acids, thereby increasing the membrane fluidity (Zhang et al ., ; Dong et al ., ).…”

The Family of Peanut Fatty Acid Desaturase Genes and a Functional Analysis of Four ω-3 AhFAD3 Members

“…3), raising the possibility that they are pseudogenes. FAD genes are known to be readily duplicated: for instance, in cucumber, 12 of the 14 FAD5s present appear to cluster closely together, suggestive of a frequent occurrence of gene duplication events following speciation (Dong et al 2016). Similarly, the cotton ω-3 FAD gene family appears to have undergone rapid expansion (Yurchenko et al 2014).…”

“…FAD2 has been shown to be required by A. thaliana to combat salinity stress, because it helps to maintain the level of desaturation of vacuolar and plasma membrane fatty acids necessary for the functioning of Na + /H + exchangers . In cucumber, some FAD genes can be induced by low temperature and repressed by high temperature, which has been taken to imply that FADs form part of the species' machinery to cope with temperature stress (Dong et al 2016). In sunflower, in contrast, a FAD2 gene has been reported as being repressible by both low temperature and salinity (Zhou et al 2017).…”

Cloning and Functional Analysis of the FAD2 Gene Family from Desert Shrub Artemisia sphaerocephala

“…Whole-genome sequencing of soybean revealed two genome duplication events occurred fifty-nine and thirteen million years ago [ 32], and seven soybean FAD2 genes were generated as a result in previous study [ 33]. In cucumber, two FAD2 genes also originated through gene duplication [ 34]. A. sphaerocephala is a cross-pollinated diploid wild plant [ 35], in the absence of genomic data, it is unclear whether this species has undergone whole-genome duplication or not.…”