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.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Salicylic acid (SA) plays a crucial role in plant innate immunity. The deployment of SA-associated immune responses is primarily affected by SA concentration, which is determined by a balance between ...SA biosynthesis and catabolism. However, the mechanisms regulating SA homeostasis are poorly understood. In this study, we characterized a unique UDP-glycosyltransferase, UGT76D1, which plays an important role in SA homeostasis and associated immune responses in Arabidopsis (Arabidopsis thaliana). Expression of UGT76D1 was induced by treatment with both the pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 and SA. Overexpression of UGT76D1 resulted in high SA accumulation, significant up-regulation of pathogen-related genes, and a hypersensitive response (HR)-like lesion mimic phenotype. This HR-like phenotype was not observed following UGT76D1 overexpression in SA-deficient NahG transgenic or sid2 plants, suggesting that the phenotype is SA dependent. Biochemical assays showed that UGT76D1 glycosylated 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA), the major catabolic forms of SA, to their Glc and Xyl conjugates in vitro and in vivo. Moreover, in a mutant background blocked in the formation of 2,3-DHBA and 2,5-DHBA, UGT76D1 overexpression did not cause a HR-like lesion mimic phenotype. Following infection with Pst DC3000, UGT76D1 knockout mutants displayed a delayed immune response, with reduced levels of DHBA glycosides and SA, and down-regulated SA synthase expression. By contrast, UGT76D1 overexpression lines showed an enhanced immune response and increased SA biosynthesis before and after pathogen infection. Thus, we propose that UGT76D1 plays an important role in SA homeostasis and plant immune responses by facilitating glycosylation of dihydroxybenzoic acids.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
• 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.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Plant systemic acquired resistance (SAR) provides an efficient broad-spectrum immune response to pathogens. SAR involves mobile signal molecules that are generated by infected tissues and transported ...to systemic tissues. Methyl salicylate (MeSA), a molecule that can be converted to salicylic acid (SA), is an essential signal for establishing SAR, particularly under a short period of exposure to light after pathogen infection. Thus, the control of MeSA homeostasis is important for an optimal SAR response. Here, we characterized a uridine diphosphate-glycosyltransferase, UGT71C3, in Arabidopsis (
), which was induced mainly in leaf tissue by pathogens including
DC3000/
(
pv tomato strain DC3000 expressing avrRpt2). Biochemical analysis indicated that UGT71C3 exhibited strong enzymatic activity toward MeSA to form MeSA glucosides in vitro and in vivo. After primary pathogen infection by
DC3000/
,
knockout mutants exhibited more powerful systemic resistance to secondary pathogen infection than that of wild-type plants, whereas systemic resistance in
overexpression lines was compromised. In agreement, after primary infection of local leaves,
knockout mutants accumulated significantly more systemic MeSA and SA than that in wild-type plants. whereas
overexpression lines accumulated less. Our results suggest that MeSA glucosylation by UGT71C3 facilitates negative regulation of the SAR response by modulating homeostasis of MeSA and SA. This study unveils further SAR regulation mechanisms and highlights the role of glucosylation of MeSA and potentially other systemic signals in negatively modulating plant systemic defense.
•Expression of UGT76C2 is downregulated by ABA and water deficit conditions.•UGT76C2 overexpression and loss of function alters the plant response to water deprivation in opposite manners.•Expression ...of stress inducible genes and cytokinin marker genes were altered in UGT76C2 overexpression and mutant plants under drought stress.
The Arabidopsis uridine diphosphate (UDP)-glycosyltransferase 76C2 (UGT76C2), a member of family 1 UGTs, is described as a cytokinin glycosyltransferase. In this study, we demonstrate a novel role of UGT76C2 in response to water deficit. QRT-PCR assay identified that the expression of this gene was downregulated by drought, osmotic stress and abscisic acid (ABA). Compared with wild type (WT) plants, transgenic lines ectopically expressing UGT76C2 exhibited reduced tolerance to ABA and osmotic stress during postgermination growth, while enhanced adaptation to drought stress at mature stage. Consistently, the ugt76c2 mutant plants showed opposite responses to these conditions. To explore the possible mechanisms of UGT76C2 contributing to drought stress adaptation, six stress inducible genes including DREB2A, RD22, RD29B, LEA, COR47 and KIN1 were detected, which showed significant upregulation in UGT76C2 overexpression plants under drought stress. Besides, five cytokinin marker genes AHK2, AHK3, AHK4, ARR1 and ARR2 were also evaluated, which showed less induced in UGT76C2 overexpression plants in response to drought stress. Our results reveal that UGT76C2, as a cytokinin glycosyltransferase, is involved in the plant response to drought stress and might represent novel cues in abiotic stress adaptation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Background and Aims
Nowadays, the plant family 1 glycosyltransferases (UGTs) are attracting more and more attention since members of this family can improve the properties of secondary ...metabolites and have significantly enriched the chemical species in plants. Over the past decade, most studies on UGTs have been conducted in Arabidopsis thaliana and they were proved to play diverse roles during the plant life cycle. The Zea mays (maize) GT1 family comprises a large number of UDP-glycosyltransferase (UGT) members. However, their enzyme activities and the biological functions are rarely revealed. In this study, a maize flavonol glycosyltransferase, UFGT2, is identified and its biological role is characterized in detail.
Methods
The UFGT2 enzyme activity, the flavonol and glycoside levels in planta were examined by high- performance liquid chromatography (HPLC) and liquid chromatography–mass spectrometry (LC-MS). The functions of UFGT2 in modifying flavonols, mediating flavonol accumulation and improving stress tolerance were analysed using two ufgt2 mutants and transgenic arabidopsis plants.
Key Results
By in vitro enzyme assay, the maize UFGT2 was found to show strong activity towards two flavonols: kaemferol and quercetin. Two ufgt2 knockout mutants, Mu689 and Mu943, exhibited obvious sensitivity to salt and drought stresses. The endogenous quercetin and kaempferol glycosides, as well as the total flavonol levels were found to be substantially decreased in the two ufgt2 mutants, with declined H2O2-scavenging capacity. In contrast, ectopic expression of UFGT2 in arabidopsis led to increased flavonol contents and enhanced oxidative tolerance. Moreover, expression of typical stress-related genes in arabidopsis and maize were affected in UFGT2 overexpression plants or knockout mutants in response to abiotic stresses. UFGT2 was also transferred into the arabidopsis ugt78d2 mutant and it was found to recover the deficient flavonol glycoside pattern in the ugt78d2 mutant, which confirmed its catalysing activity in planta.
Conclusion
It is demonstrated in our study that a maize glycosyltransferase, UFGT2, involved in modifying flavonols, contributes to improving plant tolerance to abiotic stresses.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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