A MADS-box transcription factor, XsMADS1 promotes fatty acid synthesis of seed kernels in Yellowhorn (Xanthoceras sorbifolium) by targeting XsSAD1/XsKCS1

Yellowhorn (Xanthoceras sorbifolium) is a highly promising woody oilseed tree species, with seed kernels that are rich in high-value components such as oleic acid and nervonic acid, which has significant economic and application potential. Our previous transcriptome analysis results indicate that XsSAD1 and XsKCS1 are potential key genes involved in the oleic acid and the nervonic acid synthesis pathway, respectively. However, the specific molecular mechanism by which XsSAD1 and XsKCS1 participate in fatty acid synthesis is still unclear. In this study, the correlation analysis results showed that the expression levels of XsSAD1 and XsKCS1 were positively correlated with the contents of the oleic acid and nervonic acid, respectively. Simultaneously, heterologous expression of XsSAD1 in Arabidopsis thaliana increased oleic acid content by 37.3 % and XsKCS1 raised nervonic acid levels by 31.4 %. Silencing the expression of XsSAD1 and XsKCS1 in the yellowhorn seeds reduced the accumulation of oleic acid and nervonic acid accordingly. Furthermore, it was found that expression level of transcription factor XsMADS1 is not only related to XsSAD1 and XsKCS1, but also binds to MBS elements in their promoters and induced their transcriptional expression. Our study elucidated a novel molecular mechanism of the XsMADS1-XsSAD1/XsKCS1 in regulating the fatty acid synthesis in yellowhorn seed kernels, which offers a theoretical basis for the genetic improvement of high-quality oil-type yellowhorn varieties.