Abstract
Background: Cinnamoyl-CoA reductase (CCR) is the first important and committed enzyme in the monolignol synthesis branch of the lignin biosynthesis (LB) pathway, catalyzing the conversion of cinnamoyl-CoAs to cinnamaldehydes and is crucial for the growth of Linum usitatissimum (flax), an important fiber crop. However, little information is available about CCR in flax (Linum usitatissimum L.). Results: In this study, we conducted a genome-wide analysis of the CCR gene family and identified a total of 22 CCR genes. The 22 CCR genes were distributed across 9 chromosomes, designated LuCCR1-LuCCR22. Multiple sequence alignment and conserved motif analyses revealed that LuCCR7/13/15/20 harbor completely conserved NADP-specific, NAD(P)-binding, and CCR signature motifs. Furthermore, each of these LuCCRs is encoded by 5 exons separated by 4 introns, a characteristic feature of functional CCRs. Phylogenetic analysis grouped LuCCRs into two clades, with LuCCR7/13/15/20 clustering with functional CCRs involved in LB in dicotyledonous plants. RNA-seq analysis indicated that LuCCR13/20 genes are highly expressed throughout all flax developmental stages, particularly in lignified tissues such as roots and stems, with increased expression during stem maturation. These findings suggest that LuCCR13/20 play crucial roles in the biosynthesis process of flax lignin. Additionally, LuCCR2/5/10/18 were upregulated under various types of abiotic stress, highlighting their potential roles in flax defense-related processes. Conclusions: This study systematically analyzes the CCR gene family (CCRGF) of flax (Linum usitatissimum L.) at the genomic level for the first time, so as to select the whole members of the CCRGF of flax and to ascertain their potential roles in lignin synthesis. Therefore, in future work, we can target genetic modification of LuCCR13/20 to optimize the content of flax lignin. As such, this research establishes a theoretical foundation for studying LuCCR gene functions and offers a new perspective for cultivating low-lignin flax varieties.