Discovery of salicyl benzoate UDP‐glycosyltransferase, a central enzyme in poplar salicinoid phenolic glycoside biosynthesis

Abstract

SUMMARY The salicinoids are anti‐herbivore phenolic glycosides unique to the Salicaceae (Populus and Salix). They consist of a salicyl alcohol glucoside core, which is usually further acylated with benzoic, cinnamic or phenolic acids. While salicinoid structures are well known, their biosynthesis remains enigmatic. Recently, two enzymes from poplar, salicyl alcohol benzoyl transferase and benzyl alcohol benzoyl transferase, were shown to catalyze the production of salicyl benzoate, a predicted potential intermediate in salicinoid biosynthesis. Here, we used transcriptomics and co‐expression analysis with these two genes to identify two UDP‐glucose‐dependent glycosyltransferases (UGT71L1 and UGT78M1) as candidate enzymes in this pathway. Both recombinant enzymes accepted only salicyl benzoate, salicylaldehyde and 2‐hydroxycinnamic acid as glucose acceptors. Knocking out the UGT71L1 gene by CRISPR/Cas9 in poplar hairy root cultures led to the complete loss of salicortin, tremulacin and tremuloidin, and a partial reduction of salicin content. This demonstrated that UGT71L1 is required for synthesis of the major salicinoids, and suggested that an additional route can lead to salicin. CRISPR/Cas9 knockouts for UGT78M1 were not successful, and its in vivo role thus remains to be determined. Although it has a similar substrate preference and predicted structure as UGT71L1, it appears not to contribute to the synthesis of salicortin, tremulacin and tremuloidin, at least in roots. The demonstration of UGT71L1 as an enzyme of salicinoid biosynthesis will open up new avenues for the elucidation of this pathway.

Cell Wall Acetylation in Hybrid Aspen Affects Field Performance, Foliar Phenolic Composition and Resistance to Biological Stress Factors in a Construct-Dependent Fashion

“…Despite this deficiency, the greater impact of the 35S promoter compared to the WP promoter on SPG profiles was obvious. The synthesis of phenolic compounds belonging to the SPG group is still unresolved due to reticulate pathways with no apparent direct connection to the most simple salicinoid, salicin (Babst et al, 2010;Fellenberg et al, 2020), although it is increasingly accepted that the specialized metabolism of phenolic compounds is tightly linked to primary metabolism (Harding et al, 2013), and our study further suggests that cell wall acetylation may indeed alter, and determine levels of, phenolic compounds in aspen.…”

UGT86C11 is a novel plant UDP-glycosyltransferase involved in labdane diterpene biosynthesis

“…S5 B and S7 ) ( 45 ). Although UGTs of the diterpene pathway were not well studied, some UGTs that participate in phenylpropanoid, sterol, and phytohormone pathways were previously characterized ( 10 , 18 , 20 , 21 , 25 , 26 , 46 , 47 , 48 ). To shortlist candidate UGTs of kalmegh diterpene pathway, a phylogenetic analysis was carried out using biochemically characterized UGTs.…”

Mycorrhiza-Tree-Herbivore Interactions: Alterations in Poplar Metabolome and Volatilome

“…Herbivory also induced salicin levels. Salicin is a β-glucoside of saligenin (salicyl alcohol) and characteristic for the defense response within the Salicaceae [31]. The volatile metabolites, styrene and benzaldehyde, were significantly elevated in the MB leaves as well as four non-volatile isoprenoids (secologanin, delphinine, cephalomannine and 2,3-bis-O-(geranylgeranyl)glycerol 1-phosphate) that also can be associated to defense responses.…”

“…Beetle-infested poplars, in addition, released an aldoxime-derived volatile nitrile, benzeneacetonitrile. Aldoximes have been shown to be especially effective defense compounds mediating plant-herbivore interactions [22,23,31].…”