Search Results (5)

Rice blast disease is a serious disease in rice caused by Magnaporthe oryzae (M. oryzae). Ascorbic acid (AsA), or vitamin C, is a strong antioxidant that prevents oxidative damage to cellular components and plays an essential role in plant defense response. GDP-D-mannose pyrophosphorylase (GMP or VTC1) is an enzyme that generates GDP-D-mannose for AsA, cell wall, and glycoprotein synthesis. The OsVTC1 gene has three homologs in the rice genome: OsVTC1-1, OsVTC1-3, and OsVTC1-8. Using OsVTC1-1 RNAi lines, this study investigated the role of the OsVTC1-1 gene during rice blast fungus inoculation. The OsVTC1-1 RNAi inoculated with rice blast fungus induced changes to cell wall monosaccharides, photosynthetic efficiency, reactive oxygen species (ROS) accumulation, and malondialdehyde (MDA) content. Additionally, the OsVTC1-1 RNAi lines were shown to be more resistant to rice blast fungus than the wild type. Genes and proteins related to defense response, plant hormone synthesis, and signaling pathways, especially salicylic acid and jasmonic acid, were up-regulated in the OsVTC1-1 RNAi lines after rice blast inoculation. These results suggest that the OsVTC1-1 gene regulates rice blast resistance through several defense mechanisms, including hormone synthesis and signaling pathways. Full article

Ascorbic acid (AsA) or Vitamin C is an antioxidant molecule and plays an important role in many biological processes in plants. GDP-D-mannose pyrophosphorylase (GMP or VTC1) catalyzes the synthesis of GDP-D-mannose, which is a precursor for AsA production and is used for cell wall polysaccharide and glycoprotein synthesis. In rice, the OsVTC1 gene consists of three homologs, including OsVTC1-1, OsVTC1-3 and OsVTC1-8. In this study, we characterized wild type (WT) and OsVTC1-1 RNAi lines (RI1-2 and RI1-3) and showed that the transcript levels of most genes in the AsA synthesis pathway, AsA content and leaf anatomical parameters in RNAi lines were reduced, revealing that OsVTC1-1 is involved in AsA synthesis. To further study the role of OsVTC1-1 gene, cell wall monosaccharide composition, transcriptome and proteome were compared, with specific attention paid to their wild type and OsVTC1-1 RNAi lines. Mannose and galactose composition (mole%) were decreased in OsVTC1-1 RNAi lines. Additionally, reduction of cell wall-associated proteins, such as kinesin, expansin, beta-galactosidase and cellulose synthase were observed in OsVTC1-1 RNAi lines. Our results suggest that OsVTC1-1 gene plays an important role in AsA synthesis and in cell wall-related processes. Full article

Background: Leishmaniasis, a vector-borne disease caused by the protozoan parasite from the genus Leishmania, is endemic to tropical and subtropical areas. Few treatments are available against leishmaniasis, with all presenting issues of toxicity, resistance, and/or cost. In this context, the development of new antileishmanial drugs is urgently needed. GDP-mannose pyrophosphorylase (GDP-MP), an enzyme involved in the mannosylation pathway, has been described to constitute an attractive therapeutic target for the development of specific antileishmanial agents. Methods: In this work, we produced, purified, and analyzed the enzymatic properties of the recombinant L. infantum GDP-MP (LiGDP-MP), a single leishmanial GDP-MP that presents mutation of an aspartate instead of an alanine at position 258, which is also the single residue difference with the homolog in L. donovani: LdGDP-MP. Results: The purified LiGDP-MP displayed high substrate and cofactor specificities, a sequential random mechanism of reaction, and the following kinetic constants: V_m at 0.6 µM·min⁻¹, K_m from 15–18 µM, k_cat from 12.5–13 min⁻¹, and k_cat/K_m at around 0.8 min⁻¹µM⁻¹. Conclusions: These results show that LiGDP-MP has similar biochemical and enzymatic properties to LdGDP-MP. Further studies are needed to determine the advantage for L. infantum of the A258D residue change in GDP-MP. Full article

Leishmaniasis is a vector-borne disease caused by the protozoan parasite Leishmania found in tropical and sub-tropical areas, affecting 12 million people around the world. Only few treatments are available against this disease and all of them present issues of toxicity and/or resistance. In this context, the development of new antileishmanial drugs specifically directed against a therapeutic target appears to be a promising strategy. The GDP-Mannose Pyrophosphorylase (GDP-MP) has been previously shown to be an attractive therapeutic target in Leishmania. In this study, a chemical library of 5000 compounds was screened on both L. infantum (LiGDP-MP) and human (hGDP-MP) GDP-MPs. From this screening, oncostemonol D was found to be active on both GDP-MPs at the micromolar level. Ten alkyl-resorcinol derivatives, of which oncostemonols E and J (2 and 3) were described for the first time from nature, were then evaluated on both enzymes as well as on L. infantum axenic and intramacrophage amastigotes. From this evaluation, compounds 1 and 3 inhibited both GDP-MPs at the micromolar level, and compound 9 displayed a three-times lower IC₅₀ on LiGDP-MP, at 11 µM, than on hGDP-MP. As they displayed mild activities on the parasite, these compounds need to be further pharmacomodulated in order to improve their affinity and specificity to the target as well as their antileishmanial activity. Full article

Ascorbic acid (AsA) has high antioxidant activities, and its biosynthesis has been well studied by engineering of a single structural gene (SG) in staple crops, such as tomato (Solanum lycopersicum). However, engineering the AsA metabolic pathway by multi-SG for biofortification remains unclear. In this study, pyramiding transgenic lines including GDP-Mannose 3′,5′-epimerase (GME) × GDP-d-mannose pyrophosphorylase (GMP), GDP-l-Gal phosphorylase (GGP) × l-Gal-1-P phosphatase (GPP) and GME × GMP × GGP × GPP, were obtained by hybridization of four key genes to get over-expression transgenic plants (GME, GMP, GGP, and GPP) in tomato. Pyramiding lines exhibited a significant increase in total ascorbate in leaves and red fruits except for GGP × GPP. Expression analysis indicated that increased accumulation of AsA in pyramiding transgenic lines is due to multigene regulation in AsA biosynthesis. Substrate feeding in leaf and fruit suggested that AsA biosynthesis was mainly contributed by the d-Man/l-Gal pathway in leaves, while alternative pathways may contribute to AsA accumulation in tomato fruit. Pyramiding lines showed an enhanced light response, stress tolerance, and AsA transport capacity. Also, fruit shape, fruit size, and soluble solids were slightly affected by pyramiding. This study provides the first comprehensive analysis of gene pyramiding for ascorbate biosynthesis in tomato. SGs pyramiding promotes AsA biosynthesis, which in turn enhances light response and oxidative stress tolerance. Also, the data revealed an alternative ascorbate biosynthesis pathway between leaves and fruit of tomato. Full article