UGT72B1 Is Involved In Lignin Biosynthesis And Flower Development In Arabidopsis

Glycosylation is a common way of decorating small molecular compounds in plants.Glycosylation modifies the corresponding aglycones to alter their activity,solubility,stability and localization.It plays important roles in hormone homeostasis,detoxification of xenobiotics,abiotic and biotic stress responses and synthesis of specialized metabolites.Therefore,glycosylation modification of small molecule compounds affects many aspects of plant growth and development.Here we demonstrate that glycosylation of a small molecule compound is critical for flower development in Arabidopsis.Loss of glycosyltransferase gene UGT72B1resulted in flower development defects.Nontargeted metabolomics analysis of UGT72B1 knockout and overexpression transgenic lines using ultra-high performance liquid chromatography-quadrupole time-of-flight(UPLC-q TOF)mass spectrometer identified vanillyl alcohol(4-hydroxy-3-methoxybenzyl alcohol)as a substrate of UGT72B1.In vitro and in vivo enzymatic analysis also showed that UGT72B1 strongly favors vanillyl alcohol as substrate.Loss of UGT72B1 caused over accumulation of vanillyl alcohol and related C₆C₁ structural metabolites,which affected flower development of plants.Bioinformatics analysis showed that UGT72B1 was co-expressed with shikimate and monolignol biosynthetic genes.In addition,absence of CAD4/5 that directly catalyze hydroxycinnamyl alcohol formation in monolignol biosynthesis pathway aggravated the phenotype of ugt72b1.Further analysis of cell wall constituents including lignin,phenolic acid compounds,flavonoids and wall-bound phenolics showed the metabolic process of vanillyl alcohol was closely related to vanillin,which was involved in the metabolic process of cell wall.Analysis results also showed vanillin biosynthesis genetically interacted with monolignol biosynthesis.These results indicated that over accumulation of vanillin biosynthesis pathway related C₆C₁structural metabolites including vanillyl alcohol affected the elasticity of pollen wall and stigma papillar cell wall in UGT72B1 knockout lines,thus the fertility of mutants was compromised.Loss of UGT72B1 also resulted in redirection of carbon flux from vanillin biosynthesis toward monolignol biosynthesis and aggravated lignification.In conclusion,this research provides the first evidence that glycosylation of vanillyl alcohol is essential for flower development and normal cell wall lignification.Moreover,it has been demonstrated that vanillin metabolites may play an important role in monolignol biosynthesis pathway and cell wall synthesis.These findings not only provide us a better understanding of the function of glycosyltransferase family in plants,but also supply exploratory evidence for the study of biosynthetic pathways of vanillin metabolites.Our work also provides a new direction for the study of flower development.