Identification of FAD family genes in the genome of Spirulina (Arthrospira platensis) microalgae and investigation of cellular functions in response to abiotic stresses

Arthrospira platensis (Spirulina) is a valuable photosynthesizing prokaryote with numerous industrial and food applications. Fatty acid desaturase enzymes (FADs) are responsible for the production of monounsaturated and polyunsaturated fatty acids. In the present study, the genome of A. platensis C1 was investigated using bioinformatics methods in order to identify ApFAD genes family. A total of 8 ApFAD genes were identified in Spirulina genome and classified into Omega, Sphingolipid, CrtR_beta-carotene-hydroxylase and Acyl-CoA groups. Four conserved histidine motifs that are essential for binding to the di-iron structures and catalytic activities were identified. Investigation of post-translational modifications of ApFAD proteins revealed a wide range of glycosylation and phosphorylation changes. Evaluation of FAD gene promoter regions revealed different types of cis-regulatory elements responsive to phytohormones and stress conditions, especially in Omega (ApFAD-6) and Acyl-lipid (ApFAD-3) desaturases. Also, protein-protein interaction networks showed the relations between ApFADs and genes involved in dealing with stresses through the biosynthetic process of secondary metabolites and electron transfer. Analysis of RNA-seq data of orthologous genes in Arabidopsis showed the potential of Omega and Acyl-lipid genes, such as ApFAD-3, ApFAD-6 and ApFAD-7, in response to various environmental stresses. In general, the results of this study can contribute to a more complete understanding of the function of FAD genes in Spirulina and lay the basis for the transgenic study of these genes with the aim of increasing the content of unsaturated fatty acids, improving the nutritional value of oils, as well as promoting the stress tolerance of plants.