Full-length tran sequencing provides insight into lignan and lignin metabolism relation

Flax (Linum usitatissimumL.) is an important economic crop worldwide. The lignin content of flax stems directly determines the quality of flax fiber, and excessively high lignin content in the fiber leads to pollutant discharge by the textile industry. Flax seeds also contain lignans, a group of compounds that are structurally similar to lignin and highly beneficial for human health. The biosynthesis of lignan and lignin occurs in the same metabolic pathway. To elucidate the metabolic relationship between these two compounds and the regulatory nodes of their metabolic processes, third generation (Iso-Seq) and second generation (Illumina) sequencing technologies were used in this study to obtain the transcriptomes of a pair of flax cultivars with significant differences in lignan content. The results showed that the differentially expressed genes (DEGs) are significantly enriched in the lignin and lignan biosynthesis pathways. Ten genes with significant differences in expression (|Log2 FC|>4) were selected for quantitative real-time polymerase chain reaction (qRT-PCR) analysis. The expression levels of these genes all were significantly different in Shuangya 4 and NEW at different stages of flax seed and stem development. We speculated that these genes were most likely closely related to the lignan and lignin metabolism. We also found that the lignan and lignin content are significantly negatively correlated with each other during flax seed and stem development. The findings of this study provide a scientific basis for the application of biotechnological methods to the development of new high-quality flax cultivars with high lignan and low lignin content.