UDP‐glycosyltransferase 72B1 catalyzes the glucose conjugation of monolignols and is essential for the normal cell wall lignification in Arabidopsis thaliana

Abstract

Glycosylation of monolignols has been found to be widespread in land plants since the 1970s. However, whether monolignol glycosylation is crucial for cell wall lignification and how it exerts effects are still unknown. Here, we report the identification of a mutant ugt72b1 showing aggravated and ectopic lignification in floral stems along with arrested growth and anthocyanin accumulation. Histochemical assays and thioacidolysis analysis confirmed the enhanced lignification and increased lignin biosynthesis in the ugt72b1 mutant. The loss of UDP-glycosyltransferase UGT72B1 function was responsible for the lignification phenotype, as demonstrated by complementation experiments. Enzyme activity analysis indicated that UGT72B1 could catalyze the glucose conjugation of monolignols, especially coniferyl alcohol and coniferyl aldehyde, which was confirmed by analyzing monolignol glucosides of UGT72B1 transgenic plants. Furthermore, the UGT72B1 gene was strongly expressed in young stem tissues, especially xylem tissues. However, UGT72B1 paralogs, such as UGT72B2 and UGT72B3, had weak enzyme activity toward monolignols and weak expression in stem tissues. Transcriptomic profiling showed that UGT72B1 knockout resulted in extensively increased transcript levels of genes involved in monolignol biosynthesis, lignin polymerization and cell wall-related transcription factors, which was confirmed by quantitative real-time PCR assays. These results provided evidence that monolignol glucosylation catalyzed by UGT72B1 was essential for normal cell wall lignification, thus offering insight into the molecular mechanism of cell wall development and cell wall lignification.

The Arabidopsis UDP‐glycosyltransferases UGT79B2 and UGT79B3, contribute to cold, salt and drought stress tolerance via modulating anthocyanin accumulation

“…Coniferin and sinapinic alcohol glucoside were extracted and their levels were determined according to Lin et al . (). Phenolic acids were extracted and analyzed with small modifications according to Li et al .…”

“…Using 2-week-old seedlings as material, flavonols were extracted according to Burbulis et al (1996) and determined spectrophotometrically at 270 nm. Coniferin and sinapinic alcohol glucoside were extracted and their levels were determined according to Lin et al (2016). Phenolic acids were extracted and analyzed with small modifications according to .…”

PbrmiR397a regulates lignification during stone cell development in pear fruit

“…The expression of six genes (PbrLAC1, PbrLAC2, PbrLAC18, PbrPOD1, PbrPOD2 and PbrUGT72E) at the injection sites was analysed by q-PCR. PbrPOD1, PbrPOD2 and PbrUGT72E are putative orthologous genes involved in the transfer of monolignols in Arabidopsis (Lin et al, 2016). Injection of the PbrmiR397a overexpression construct decreased the expression of PbrLAC1, PbrLAC2 and PbrLAC18 but increased the expression of PbrPOD1, PbrPOD2 and PbrUGT72E.…”

Compensatory guaiacyl lignin biosynthesis at the expense of syringyl lignin in4CL1-knockout poplar

“…As F5Hs occupy the branch-point into S lignin biosynthesis, their downregulation is consistent with the preferential reduction of S lignin in 4cl1 mutants. Other genes implicated in lignification, including a UDP-glycosyltransferase (Potri.014G096100) orthologous to Arabidopsis UGT72B1 involved in monolignol glycosylation (Lin et al, 2016) and a laccase (Potri.010G193100) involved in oxidative coupling of monolignols (Ranocha et al, 2002; Lu et al, 2013), were also downregulated in the mutants (Figure 4A). In contrast, transcript levels of two lignin genes increased significantly, and they encode enzymes acting immediately upstream (caffeoyl shikimate esterase, CSE1) and downstream (caffeoyl-CoA O -methyltransferase, CCoAOMT1) of the 4CL reaction with caffeic acid.…”