Tomato <i>γ</i>-Glutamylhydrolases: Expression, Characterization, and Evidence for Heterodimer Formation

Akhtar, Tariq A.; McQuinn, Ryan P.; Naponelli, Valeria; Gregory, Jesse F.; Giovannoni, James J.; Hanson, Andrew D.

doi:10.1104/pp.108.124479

Cited by 19 publications

(17 citation statements)

References 28 publications

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“…The recycling of pABAGlu/pABAGlu n starts with an enzymatic cleavage of the Glu tail, if any present, mediated by gamma-glutamyl hydrolase (GGH) (Figure 3) (Akhtar et al, 2008, 2010). The enzyme is located in vacuoles (Orsomando et al, 2005; Akhtar et al, 2008). Despite a very high GGH activity, polyglutamylated folates still exist in vacuoles.…”

Section: Folate Salvagementioning

confidence: 99%

Folates in Plants: Research Advances and Progress in Crop Biofortification

et al. 2017

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Folates, also known as B9 vitamins, serve as donors and acceptors in one-carbon (C1) transfer reactions. The latter are involved in synthesis of many important biomolecules, such as amino acids, nucleic acids and vitamin B5. Folates also play a central role in the methyl cycle that provides one-carbon groups for methylation reactions. The important functions fulfilled by folates make them essential in all living organisms. Plants, being able to synthesize folates de novo, serve as an excellent dietary source of folates for animals that lack the respective biosynthetic pathway. Unfortunately, the most important staple crops such as rice, potato and maize are rather poor sources of folates. Insufficient folate consumption is known to cause severe developmental disorders in humans. Two approaches are employed to fight folate deficiency: pharmacological supplementation in the form of folate pills and biofortification of staple crops. As the former approach is considered rather costly for the major part of the world population, biofortification of staple crops is viewed as a decent alternative in the struggle against folate deficiency. Therefore, strategies, challenges and recent progress of folate enhancement in plants will be addressed in this review. Apart from the ever-growing need for the enhancement of nutritional quality of crops, the world population faces climate change catastrophes or environmental stresses, such as elevated temperatures, drought, salinity that severely affect growth and productivity of crops. Due to immense diversity of their biochemical functions, folates take part in virtually every aspect of plant physiology. Any disturbance to the plant folate metabolism leads to severe growth inhibition and, as a consequence, to a lower productivity. Whereas today's knowledge of folate biochemistry can be considered very profound, evidence on the physiological roles of folates in plants only starts to emerge. In the current review we will discuss the implication of folates in various aspects of plant physiology and development.

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Section: Folate Salvagementioning

confidence: 99%

Folates in Plants: Research Advances and Progress in Crop Biofortification

et al. 2017

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“…In bacteria, overexpression of GGH causes extensive deconjugation of polyglutamates and decreased folate retention, without a major effect on growth rate (Sybesma et al. , 2003; Akhtar et al. , 2008).…”

Section: Introductionmentioning

confidence: 99%

“…To further examine this relationship, we turned to the recently described GGH systems of Arabidopsis and tomato ( Solanum lycopersicum ) (Orsomando et al. , 2005; Akhtar et al. , 2008).…”

Section: Introductionmentioning

confidence: 99%

A central role for gamma-glutamyl hydrolases in plant folate homeostasis

et al. 2010

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SUMMARYMost cellular folates carry a short poly-c-glutamate tail, and this tail is believed to affect their efficacy and stability. The tail can be removed by c-glutamyl hydrolase (GGH; EC 3.4.19.9), a vacuolar enzyme whose role in folate homeostasis remains unclear. In order to probe the function of GGH, we modulated its level of expression and subcellular location in Arabidopsis plants and tomato fruit. Three-fold overexpression of GGH in vacuoles caused extensive deglutamylation of folate polyglutamates and lowered the total folate content by approximately 40% in Arabidopsis and tomato. No such effects were seen when GGH was overexpressed to a similar extent in the cytosol. Ablation of either of the major Arabidopsis GGH genes (AtGGH1 and AtGGH2) alone did not significantly affect folate status. However, a combination of ablation of one gene plus RNA interference (RNAi)-mediated suppression of the other (which lowered total GGH activity by 99%) increased total folate content by 34%. The excess folate accumulated as polyglutamate derivatives in the vacuole. Taken together, these results suggest a model in which: (i) folates continuously enter the vacuole as polyglutamates, accumulate there, are hydrolyzed by GGH, and exit as monoglutamates; and (ii) GGH consequently has an important influence on polyglutamyl tail length and hence on folate stability and cellular folate content.

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“…Recently this ubiquitous enzyme has been well characterized in soy, tomato, and Arabidopsis . 23,37,38 Plants usually have several GGH genes, although animals have only one. Several plant isoforms of GGH have been described with various pH optima and substrate specificities.…”

Section: Resultsmentioning

confidence: 99%

Influence of High-Pressure Processing on the Profile of Polyglutamyl 5-Methyltetrahydrofolate in Selected Vegetables

Wang

Riedl

Somerville

et al. 2011

J. Agric. Food Chem.

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In plants, folate occurs predominantly as 5-methyltetrahydrofolate (5MTHF) polyglutamyl forms. Differences in stability and bioavailability of food folate compared to synthetic folic acid have been attributed to the presence of the polyglutamyl chain. High-pressure processing (HPP) was tested for whether it might shorten polyglutamyl chains of 5MTHF species in fresh vegetables by enabling action of native γ-glutamylhydrolase (GGH). A validated ultrahigh-performance reversed-phase liquid chromatography–tandem mass spectrometry method using stable isotope as internal standard was applied for characterizing 5MTHF polyglutamyl profiles. HPP conditions included 300, 450, and 600 MPa at 30 °C for 0 or 5 min, and vegetables were vacuum-packed before treatment. Investigated vegetables included cauliflower (Brassica oleracea), baby carrots (Daucus carota), and carrot greens (D. carota). HPP treatment caused conversion of polyglutamyl 5MTHF species to short-chain and monoglutamyl forms. Maximal conversion of polyglutamyl folate to monoglutamyl folate occurred at the highest pressure/time combination investigated, 600 MPa/30 °C/5 min. Under this condition, cauliflower monoglutamyl folate increased nearly 4-fold, diglutamyl folate 32-fold, and triglutamyl folate 8-fold; carrot monoglutamyl increased 23-fold and diglutamyl 32-fold; and carrot greens monoglutamyl increased 2.5-fold and the diglutamyl form 19-fold. Although some folate degradation was observed at certain intermediate HPP conditions, total 5MTHF folate was largely preserved at 600 MPa/5 min. Thus, HPP of raw vegetables is a feasible strategy for enhancing vegetable monoglutamate 5MTHF.

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Tomato γ-Glutamylhydrolases: Expression, Characterization, and Evidence for Heterodimer Formation

Cited by 19 publications

References 28 publications

Folates in Plants: Research Advances and Progress in Crop Biofortification

Folates in Plants: Research Advances and Progress in Crop Biofortification

A central role for gamma-glutamyl hydrolases in plant folate homeostasis

Influence of High-Pressure Processing on the Profile of Polyglutamyl 5-Methyltetrahydrofolate in Selected Vegetables

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