Identification and Analysis of KAS II, FAT, SAD, and FAD Gene Families in Hippophae rhamnoides

<i>KAS II</i> (β-ketoacyl-acyl carrier protein (ACP) synthases II), <i>FAT</i> (fatty acid thioesterases), <i>SAD</i> (stearoyl-ACP desaturase), and <i>FAD</i> (fatty acid desaturases) are the vital gene families involved in fatty acid (FA) synthesis in <i>Hippophae rhamnoides</i> L. However, information on the number and location of these genes and which ones are key to the formation of FAs in fruit seeds and pulp was not complete. Our study aimed to solve this issue using the available genomic sequences and transcriptome data that we obtained. We compared the protein sequences of sea buckthorn with those of <i>Arabidopsis thaliana</i> and checked for the presence of conserved domains. As a result of structure and phylogenetic analyses, 4 <i>KAS II</i>, 8 <i>FAT</i>, 9 <i>SAD</i>, and 12 <i>FAD</i> genes were identified in the <i>H. rhamnoides</i> genome, which were classified into subfamilies: <i>KAS II, FATA</i>, <i>FATB</i>, <i>FAD2</i>, <i>FAD3</i>, <i>FAD6</i>, and <i>FAD7/8</i>. To analyze the expression of the identified genes, we sequenced the transcriptomes of sea buckthorn seeds and fruit pulp at four development stages, as well as leaves. The analysis revealed representatives of the <i>FAT</i>, <i>SAD</i>, and <i>FAD</i> families with high tissue-and stage-specific expression in seeds and pulp. These genes are likely to play a key role in the biosynthesis of sea buckthorn FAs. The obtained results may help to establish the precise biosynthesis mechanisms of FAs and will promote the breeding of new sea buckthorn varieties that have oil with a defined FA composition.