Summary
The plant family 1 UDP‐glycosyltransferases (UGTs) are the biggest GT family in plants, which are responsible for transferring sugar moieties onto a variety of small molecules, and control ...many metabolic processes; however, their physiological significance in planta is largely unknown. Here, we revealed that two Arabidopsis glycosyltransferase genes, UGT79B2 and UGT79B3, could be strongly induced by various abiotic stresses, including cold, salt and drought stresses. Overexpression of UGT79B2/B3 significantly enhanced plant tolerance to low temperatures as well as drought and salt stresses, whereas the ugt79b2/b3 double mutants generated by RNAi (RNA interference) and CRISPR‐Cas9 strategies were more susceptible to adverse conditions. Interestingly, the expression of UGT79B2 and UGT79B3 is directly controlled by CBF1 (CRT/DRE‐binding factor 1, also named DREB1B) in response to low temperatures. Furthermore, we identified the enzyme activities of UGT79B2/B3 in adding UDP‐rhamnose to cyanidin and cyanidin 3‐O‐glucoside. Ectopic expression of UGT79B2/B3 significantly increased the anthocyanin accumulation, and enhanced the antioxidant activity in coping with abiotic stresses, whereas the ugt79b2/b3 double mutants showed reduced anthocyanin levels. When overexpressing UGT79B2/B3 in tt18 (transparent testa 18), a mutant that cannot synthesize anthocyanins, both genes fail to improve plant adaptation to stress. Taken together, we demonstrate that UGT79B2 and UGT79B3, identified as anthocyanin rhamnosyltransferases, are regulated by CBF1 and confer abiotic stress tolerance via modulating anthocyanin accumulation.
Significance Statement
The physiological roles of most UDP‐glycosyltransferases (UGTs) are unknown. Here, we used overexpression and RNA interference or CRISPR‐Cas9 strategies to show that two anthocyanin rhamnosyltransferases play crucial roles in enhancing tolerance to cold, salt and drought.
Summary
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.
Significance Statement
Lignin provides mechanical support to plant stems and helps protect plants from pathogen attack. Although monolignol glucosides were reported in planta in the 1970s, whether they were important for cell wall lignification was unknown. Here we characterize a mutant in a UDP‐glycosyl transferase and show that monolignol glucosylation indeed plays an essential role in normal cell wall lignification.
SUMMARY
Recent studies have shown that global metabolic reprogramming is a common event in plant innate immunity; however, the relevant molecular mechanisms remain largely unknown. Here, we ...identified a pathogen‐induced glycosyltransferase, UGT73C7, that plays a critical role in Arabidopsis disease resistance through mediating redirection of the phenylpropanoid pathway. Loss of UGT73C7 function resulted in significantly decreased resistance to Pseudomonas syringae pv. tomato DC3000, whereas constitutive overexpression of UGT73C7 led to an enhanced defense response. UGT73C7‐activated immunity was demonstrated to be dependent on the upregulated expression of SNC1, a Toll/interleukin 1 receptor‐type NLR gene. Furthermore, in vitro and in vivo assays indicated that UGT73C7 could glycosylate p‐coumaric acid and ferulic acid, the upstream metabolites in the phenylpropanoid pathway. Mutations that lead to the loss of UGT73C7 enzyme activities resulted in the failure to induce SNC1 expression. Moreover, glycosylation activity of UGT73C7 resulted in the redirection of phenylpropanoid metabolic flux to biosynthesis of hydroxycinnamic acids and coumarins. The disruption of the phenylpropanoid pathway suppressed UGT73C7‐promoted SNC1 expression and the immune response. This study not only identified UGT73C7 as an important regulator that adjusts phenylpropanoid metabolism upon pathogen challenge, but also provided a link between phenylpropanoid metabolism and an NLR gene.
Significance Statement
Global metabolic reprogramming is a common event in plant innate immunity; however, the relevant molecular mechanisms remain largely unknown. Here, we identified that the pathogen‐induced glycosyltransferase UGT73C7 is an important regulator that adjusts phenylpropanoid metabolism upon pathogen challenge and promotes SNC1‐dependent Arabidopsis immunity, thus providing a link between phenylpropanoid metabolism and an NLR gene.
Key message
This study revealed that the Arabidopsis UGT75B1 plays an important role in modulating ABA activity by glycosylation when confronting stress environments.
The cellular ABA content and ...activity can be tightly controlled in several ways, one of which is glycosylation by family 1 UDP-glycosyltransferases (UGTs). Previous analysis has shown UGT75B1 activity towards ABA in vitro. However, the biological role of UGT75B1 remains to be elucidated. Here, we characterized the function of UGT75B1 in abiotic stress responses via ABA glycosylation. GUS assay and qRT-PCR indicated that
UGT75B1
is significantly upregulated by adverse conditions, such as osmotic stress, salinity and ABA. Overexpression of
UGT75B1
in Arabidopsis leads to higher seed germination rates and seedling greening rates upon exposure to salt and osmotic stresses. In contrast, the big
UGT75B1
overexpression plants are more sensitive under salt and osmotic stresses. Additionally, the
UGT75B1
overexpression plants showed larger stomatal aperture and more water loss under drought condition, which can be explained by lower ABA levels examined in
UGT75B1
OE plants in response to water deficit conditions. Consistently,
UGT75B1
ectopic expression leads to downregulation of many ABA-responsive genes under stress conditions, including
ABI3, ABI5
newly germinated seedlings and
RD29A
,
KIN1
,
AIL1
in big plants. In summary, our results revealed that the Arabidopsis UGT75B1 plays an important role in coping with abiotic stresses via glycosylation of ABA.
• Family 1 glycosyltransferases comprise the greatest number of glycosyltransferases found in plants. The widespread occurrence and diversity of glycosides throughout the plant kingdom underscore the ...importance of these glycosyltransferases. • Here, we describe the identification and characterization of a late‐flowering Arabidopsis (Arabidopsis thaliana) mutant, in which a putative family 1 glycosyltransferase gene, UGT87A2, was disrupted. The role and possible mechanism of UGT87A2 in the regulation of flowering were analyzed by molecular, genetic and cellular approaches. • The ugt87a2 mutant exhibited late flowering in both long and short days, and its flowering was promoted by vernalization and gibberellin. Furthermore, the mutant flowering phenotype was rescued by the wild‐type UGT87A2 gene in complementation lines. Interestingly, the expression of the flowering repressor FLOWERING LOCUS C was increased substantially in the mutant, but decreased to the wild‐type level in complementation lines, with corresponding changes in the expression levels of the floral integrators and floral meristem identity genes. The expression of UGT87A2 was developmentally regulated and its protein products were distributed in both cytoplasm and nucleus. • Our findings imply that UGT87A2 regulates flowering time via the flowering repressor FLOWERING LOCUS C. These data highlight an important role for the family 1 glycosyltransferases in the regulation of plant flower development.
Glycosyltransferase (GT) family‐1, the biggest GT family in plants, typically participates in modification of small molecules and affects many aspects during plant development. In Arabidopsis ...thaliana, although some UDP glycosyltransferases (UGTs) of family‐1 have been functionally characterized, functions of most the UGTs remain unknown or fragmentary. Here, we report data for the Arabidopsis UGT87A2, a stress‐regulated GT. We found that UGT87A2 could be dramatically induced by salinity, osmotic stress, drought and ABA. Overexpression of UGT87A2 (87A2OE) leads to accelerated germination and greening, higher survival rate as well as increased root length against abiotic stresses compared with those of wild‐type (WT) plants. In addition, we observed lower water loss rate in the 87A2OE plants due to smaller stomatal apertures. The transgenic plants also showed reduced levels of H2O2 and superoxide under low water status compared with those of WT plants. Consistently, function loss of UGT87A2 in ugt87a2 knockout lines resulted in opposite performances under these conditions. A transcriptome profiling revealed that 121 genes were differentially regulated upon UGT87A2 overexpression, and a large number of stress‐induced genes were upregulated in UGT87A2 overexpression plants. Expression of seven genes among them were assessed by quantitative real‐time polymerase chain reaction (qRT‐PCR), including CPK32, CYP81F2, MYB96, DREB2A, FBS1, PUB23 and RAV2 under both control and stress treatments, and the results greatly validated our transcriptome data. Taken together, our findings support an explicit role of UGT87A2 in adaptation to abiotic stresses.
Drought is one of the most important environmental constraints affecting plant growth and development and ultimately leads to yield loss. Uridine diphosphate (UDP)-dependent glycosyltransferases ...(UGTs) are believed to play key roles in coping with environmental stresses. In rice, it is estimated that there are more than 200
genes. However, most of them have not been identified as their physiological significance. In this study, we reported the characterization of a putative glycosyltransferase gene
in rice.
gene is significantly upregulated by drought stress and abscisic acid (ABA) treatment. The overexpression of
led to an enhanced tolerance in transgenic rice plants to drought stress, while the
mutants of rice showed a more sensitive phenotype to drought stress. Further studies indicated that
overexpression induced ABA accumulation, stomatal closure, enhanced reactive oxygen species (ROS) scavenging capacity, increased proline and sugar contents, and upregulated expression of stress-related genes under drought stress conditions. Moreover, when
was ectopically overexpressed in Arabidopsis, the transgenic plants showed increased tolerance to drought as well as in rice. Our findings suggest that
plays an important role in mediating plant response to drought and oxidative stresses. This work may provide a promising candidate gene for cultivating drought-tolerant crops both in dicots and monocots.
Abiotic stresses greatly influence plant growth and productivity. While glycosyltransferases are widely distributed in plant kingdom, their biological roles in response to abiotic stresses are ...largely unknown. In this study, a novel Arabidopsis glycosyltransferase gene UGT85A5 was identified as significantly induced by salt stress. Ectopic expression of UGT85A5 in tobacco enhanced the salt stress tolerance in the transgenic plants. There were higher seed germination rates, better plant growth and less chlorophyll loss in transgenic lines compared to wild type plants under salt stress. This enhanced tolerance of salt stress was correlated with increased accumulations of proline and soluble sugars, but with decreases in malondialdehyde accumulation and Na(+)/K(+) ratio in UGT85A5-expressing tobacco. Furthermore, during salt stress, expression of several carbohydrate metabolism-related genes including those for sucrose synthase, sucrose-phosphate synthase, hexose transporter and a group2 LEA protein were obviously upregulated in UGT85A5-expressing transgenic plants compared with wild type controls. Thus, these findings suggest a specific protective role of this glycosyltransferase against salt stress and provide a genetic engineering strategy to improve salt tolerance of crops.
Auxin is one type of phytohormones that plays important roles in nearly all aspects of plant growth and developmental processes. The glycosylation of auxins is considered to be an essential mechanism ...to control the level of active auxins. Thus, the identification of auxin glycosyltransferases is of great significance for further understanding the auxin regulation. In this study, we biochemically screened the group L of Arabidopsis thaliana glycosyltransferase superfamily for enzymatic activity toward auxins. UGT74D1 was identified to be a novel auxin glycosyltransferase. Through HPLC and LC-MS analysis of reaction products in vitro by testing eight substrates including auxins and other compounds, we found that UGT74D1 had a strong glucosylating activity toward indole-3-butyric acid IBA, indole-3-propionic acid IPA, indole-3-acetic acid IAA and naphthaleneacetic acid NAA, catalyzing them to form corresponding glucose esters. Biochemical characterization showed that this enzyme had a maximum activity in HEPES buffer at pH 6.0 and 37°C. In addition, the enzymatic activity analysis of crude protein and the IBA metabolite analysis from transgenic Arabidopsis plants overexpressing UGT74D1 gene were also carried out. Experimental results indicated that over-production of the UGT74D1 in plants indeed led to increased level of the glucose conjugate of IBA. Moreover, UGT74D1 overexpression lines displayed curling leaf phenotype, suggesting a physiological role of UGT74D1 in affecting the activity of auxins. Our current data provide a new target gene for further genetic studies to understand the auxin regulation by glycosylation in plants.
Cytokinins are a class of phytohormones that play a crucial role in plant growth and development. The gene UGT76C2 encoding cytokinin N-glucosyltransferase of Arabidopsis thaliana has been previously ...identified. To determine the in planta role of UGT76C2 in cytokinin metabolism and response, we analyzed the phenotypes of its loss-of-function mutant (ugt76c2) and its overexpressors. The accumulation level of the cytokinin N-glucosides was significantly decreased in ugt76c2, but substantially increased in UGT76C2 overexpressors compared with the wild type. When treated with exogenously applied cytokinin, ugt76c2 showed more sensitivity and UGT76C2 overexpressors showed less sensitivity to cytokinin in primary root elongation, lateral root formation, Chl retention and anthocyanin accumulation. Under normal growth conditions ugt76c2 had smaller seeds than the wild type, with accompanying lowered levels of active and N-glucosylated cytokinin forms. The expression levels of cytokinin-related genes such as AHK2, AHK3, ARR1, IPT5 and CKX3 were changed in ugt76c2, suggesting homeostatic control of cytokinin activity. Studies of spatiotemporal expression patterns showed that UGT76C2 was expressed at a relatively higher level in the seedling and developing seed. In their entirety, our data, based mainly on this comparison and opposite phenotypes of knockout and overexpressors, strongly suggest that UGT76C2 is involved in cytokinin homeostasis and cytokinin response in planta through cytokinin N-glucosylation.
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