Comprehensive analysis of the UDP‑glycosyltransferase gene family in flax [Linum usitatissimum L.] and functional verification of the role of LuUGT175 in the regulation of lignin biosynthesis

Flax (Linum usitatissimum L.) is an important fiber crop worldwide, but the lignin in L. usitatissimum fiber leads to hard and brittle fiber, reducing its quality and resulting in poor spinnability. UDP glycosyltransferases (UGTs) play an important role in plant secondary metabolism. Therefore, the identification and characterization of L. usitatissimum UGTs and the screening and validation of UGTs related to lignin biosynthesis are research priorities. In this study, the conserved PSPG motif was used to identify 190 L. usitatissimum UGT genes (LuUGTs) with uneven distribution on chromosomes and scaffolds. The genes were divided into 16 phylogenetic groups. L. usitatissimum UGT family members in the same groups had similar protein motifs and gene structures, but there were some differences between the groups. Whole genome duplication and segmental duplication were the main replication events that led to the expansion of the L. usitatissimum UGT family. The expression patterns of LuUGTs in different tissues and at different developmental stages of L. usitatissimum can be divided into three types: low expression, constitutive expression, and tissue-specific expression. It was found that lack of function of LuUGT175 in L. usitatissimum led to slow plant growth, serious lignification in stems and ectopic lignification in fibers. LuNAC61 was identified as an upstream negative regulator of LuUGT175. In vivo and in vitro validation confirmed a direct interaction between the two. Our research provides key theoretical and material support for an in-depth and comprehensive understanding of the mechanism of L. usitatissimum lignin synthesis and the use of biotechnology to reduce the lignin content of L. usitatissimum fiber. It also provides an important breakthrough and a research opportunity for analyzing the contribution of glycosylation to lignin metabolism and cell wall lignification.