Comprehensive evolutionary analysis of the FAD2 gene family in representatives of campanulids: identification and characterization of candidate genes from the plant polyacetylene metabolism

Abstract

Background Polyacetylenes (PAs) are a kind of specialized plant defense compounds that mainly occur in campanulid plants. Fatty Acid Desaturase 2 (FAD2) catalyzes desaturation in the initial stage of PA biosynthesis, and tends to be involved in later steps of oxidation reactions as well. The FAD2 enzymes not only have desaturase activity, but can also perform other fatty acid modifications, giving rise to various unusual fatty acids, including the precursors to PAs.Methods and results We present a genome-wide survey of FAD2 genes in nine species, covering all main families of PA source in campanulids and the model plant Solanum lycopersicum, and reconstruct the evolutionary history of this gene family. We uncovered the high conservatism of motif composition, gene structural characteristics and expression patterns of the FAD2 members, in spite of their functional diversification. The number of genes expanded extensively in Asterales and Apiales, two main clades of campanulids, by various gene duplication.Conclusion We provided a list of FAD2 candidates that potentially underlying the biosynthesis of PAs using an approach integrating the phylogenetic framework and molecular evolution rates studies. This work will significantly broaden our perspective on the functional diversity of FAD2 enzymes, and lay a foundation for subsequent functional analysis aimed at discovering further FAD2 genes involved in PA biosynthesis.