Glucosyltransferase CsUGT78A14 Regulates Flavonols Accumulation and Reactive Oxygen Species Scavenging in Response to Cold Stress in Camellia sinensis

Abstract

Glycosyltransferases (UGTs) play diverse roles in cellular metabolism by altering regulatory metabolites activities. However, the physiological roles of most members of UGTs in crops in response to abiotic stresses are unknown. We have identified a novel glycosyltransferase CsUGT78A14 in tea crops, an important economic crops, whose expression is strongly induced by cold stress. Biochemical analyses confirmed that CsUGT78A14-1 showed the highest activity toward kaempferol and is involved in the biosynthesis of kaempferol-diglucoside, whereas the product of CsUGT78A14-2, which differs from CsUGT78A14-1 by a single amino acid, was identified as 3-O-glucoside. The accumulation of kaempferol monoglucosides and diglucosides was consistent with the expression levels of CsUGT78A14 in response to cold stress, as well as in different tissues and genotypes of tea plants. Down-regulation of CsUGT78A14 resulted in reduced accumulation of flavonols, reactive oxygen species (ROS) scavenging capacity and finally reduced tea plant stress tolerance under cold stress. The antioxidant capacity of flavonols aglycon was enhanced by glucosylation catalyzed by CsUGT78A14. The results demonstrate that CsUGT78A14 plays a critical role in cold stress by increasing flavonols accumulation and ROS scavenging capacity, providing novel insights into the biological role of UGTs and flavonoids in plants.

Sesquiterpene glucosylation mediated by glucosyltransferase UGT91Q2 is involved in the modulation of cold stress tolerance in tea plants

“…To silence UGT91Q2 in the tea leaves still attached to the whole plant, 1 ml 20 μM AsODN UGT91Q2 solution was injected into tea plant seedlings, tea plant seedlings injected with the sense oligonucleotides (sODN) were used as control. After 24 h incubation, the leaves were harvested and kept at −8°C before analysis (Zhao et al , ).…”

You Want it Sweeter: How Glycosylation Affects Plant Response to Oxidative Stress

“…Furthermore, increased kaempferol and quercetin content obtained by transient overexpression in tobacco of the Crocus sativus CsBGLU12 , coding for a β-glucosidase active on flavonol glycosides, resulted in leaves more tolerant to ultraviolet B, dehydration and salt exposure, as shown by higher chlorophyll content and lower lipid peroxidation after stress application ( Baba et al, 2017 ). We may suggest that the phenotypes related to oxidative stress tolerance observed in tea with down-regulation of UGT78A14 ( Zhao et al, 2019 ) and tobacco with over-expression of CsBGLU12 ( Baba et al, 2017 ) are partially explained by different pools of antioxidant molecules, which are not restricted to the few flavonoids developed in this review. Other specialized metabolites, whose molecular structures and contents are highly variable between distinct species, may explain this difference.…”

“…These observations suggest that UGTs partake in plant global response to abiotic stresses. For instance, the down-regulation of two UGT s from tea, UGT78A14 and UGT91Q2 , was shown to result in lower tolerance to cold stress ( Zhao et al, 2019 ; Zhao et al, 2020 ), which also triggers oxidative stress. Interestingly, expression of these two genes is cold-inducible, suggesting that their function in planta is closely related to tolerance to this abiotic stress.…”

“…Their leaves are characterized by an increased accumulation of superoxide radicals and H 2 O 2 , which may result in lipid peroxidation and decreased photosynthetic efficiency. The UGT78A14 glycosylation products of kaempferol and quercetin have higher ROS scavenging activity than their corresponding aglycones as assessed by FRAP, DPPH and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays ( Zhao et al, 2019 ). This result is contradictory to previous observations, which stated that flavonoid aglycones show higher antioxidant capacity than their glycosylated forms, as demonstrated for quercetin and luteolin using another method, the Trolox equivalent antioxidant activity (TEAC) test ( Rice-Evans et al, 1996 ; Hopia and Heinonen, 1999 ; Montoro et al, 2005 ).…”

“…Other specialized metabolites, whose molecular structures and contents are highly variable between distinct species, may explain this difference. Moreover, Zhao and colleagues ( 2019 ) investigated tolerance to cold stress, while Baba and colleagues ( 2017 ) focused on ultraviolet B, dehydration and salt exposure. While all these conditions result in oxidative stress, they most likely do not invoke the same cellular and molecular consequences and responses.…”