De novo assembly of transcriptome and unsaturated fatty acid biosynthesis candidate genes Mining and functional Identification.

Unsaturated fatty acids (UFA) in lipids are the key to nutraceutical oil applications, with various potential applications in nutraceutical functional foods and pharmaceutical industries. In (Salicaceae), more than 80 % of UFA have been found in the fruits; yet, the underlying genetic mechanism remains poorly understood. Due to the lack of theoretical research on the genes related to lipid biosynthesis and the complete genetic transformation system of fruit, the selection and breeding of , an excellent oil tree, has been severely restricted. In-depth understanding of the molecular mechanism and gene function of lipid biosynthesis of fruit is therefore of great significance for the development of resources. This is not only conducive to the genetic improvement of by molecular breeding technologies but can also provide a reference for the study of the gene functions of other oil plants. In this study, the FA accumulation patterns of fruits during 8 growth periods were analysed. Fruit from two developmental periods with different UFA levels were analysed for RNA sequencing by an Illumina NovaSeq 6000 HiSeq platform. transcriptome assembly presented 115,350 unigenes and 4382 differentially expressed genes (DEGs). Functional annotation in the KEGG pathway and combined with DEG data revealed candidate genes potentially involved in UFA biosynthesis. Expression analysis of q-PCR of and suggested that these genes are highly involved in UFA biosynthesis. Full-length candidate genes were cloned and analysed by bioinformatic tools, and function analysis of and showed that these genes regulated the products of linoleic acid metabolism. This study provides a foundation for UFA biosynthesis in , facilitating its genetic breeding in the future.