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.

Expression characteristics of predicted CesA/Csl genes of fiber flax variety ‘Diana’ were investigated using RNA-seq data obtained during the fast-growing stage. First, flax stem anatomic analysis revealed differing developmental processes from bottom to top, with middle and lower stem fiber cells exhibiting significantly thickened cell walls. Moreover, stem cellulose/hemicellulose content exhibited positional biases, with a top-to-bottom increase in cellulose content and bottom-to-top increase in hemicellulose content observed. Most CesA/Csl genes were predominantly expressed in stems, roots, and less in leaves. The correlations between the expression levels of CesA/Csl genes and the contents of cellulose and hemicellulose were analyzed. The expression levels of LuCesA4, LuCesA8A and LuCesA8B genes showed significantly positive correlations with cellulose content (P < 0.05), while expression levels of two LuCesA3, three LuCesA6, two LuCslA2, and four LuCslC genes revealed significantly positive correlations with hemicellulose content (P < 0.05). CesA/Csl protein interaction network analysis revealed five transcription factors (TFs) that had high protein–protein interaction (PPI) scores with CesA/Csl proteins: LuNAC10 (Lus10015392), LuNAC12 (Lus10001664), LuNAM (Lus10017915), LuMyb42 (Lus10038913), LuMyb46 (Lus10027369). Therefore, these TFs may play critical regulatory roles in cellulose/hemicellulose synthesis. This study provides a theoretical foundation for investigating flax fiber cell wall synthesis and regulatory mechanisms.

Hyperhydricity is a frequently occurring physiological disorder in plant tissue culture that impairs the regeneration and survival of vitrified plant materials, leading to significant losses and complicating research applications. Although numerous studies have focused on strategies to mitigate hyperhydricity, its molecular mechanisms remain poorly characterized. In this study, transcriptome sequencing and endogenous hormone content analysis were conducted on hyperhydric and normal callus of flax (Linum usitatissimum L.). Transcriptomic analysis revealed 2698 differentially expressed genes (DEGs) between these two tissue types. Pathway analysis through KEGG demonstrated that these DEGs predominantly linked to metabolic processes including phenylpropanoid formation, MAPK signaling cascades, and plant hormone signal transduction. Moreover, quantification of endogenous hormone levels indicated a significant reduction in all hormones except cytokinins (ZRs) in hyperhydric tissues. The observed disruption in endogenous hormone levels suggests its potential role in the development of plant vitrification. These findings provide valuable insights into the molecular processes underlying hyperhydricity, contributing to a more comprehensive understanding of this phenomenon.