Genome-Wide Identification and Expression Pattern Analysis of the F5H Gene Family in Flax (Linum usitatissimum L.)

Ferulate 5-hydroxylase (F5H) is a cytochrome P450-dependent monooxygenase that plays a key role in the biosynthesis of syringyl (S) lignin. In this study, mining of flax (Linum usitatissimum) genomic data enabled the identification of nine LuF5H genes. Bioinformatics analysis revealed the physicochemical properties, gene structures, conserved motifs, phylogenetic evolutionary features and promoter cis-acting elements related to these genes and their encoded proteins. Based on the gene structural and phylogenetic features, the nine LuF5Hs were assigned to two subclasses. The expression levels of the nine LuF5Hs was analyzed by the RNA-seq technique, and the RNA-seq data were verified by qRT-PCR. The results of the RNA-seq analysis showed that LuF5H genes belonging to the same subclass exhibited similar expression patterns. Notably, the transcripts of the LuF5H3 and LuF5H7 subclass 1 genes accumulated at high levels in stem tissues, thus indicating that LuF5H3 and LuF5H7 are the main LuF5H genes involved in flax lignin biosynthesis. Furthermore, the expression levels of LuF5H1, LuF5H3, LuF5H4 and LuF5H7 were upregulated 1.2-1.9-fold under drought, NaCl stress and brassinosteroid treatment conditions. This first comprehensive study of the flax F5H gene family provides valuable data for use in gene function analysis toward improving flax fiber quality and reducing flax manufacturing costs and associated environmental pollution.