Validamycin Research Articles

Control efficacy of validamycin A against Fusarium wilt correlated with the severity of phytotoxic necrosis formed on tomato tissues

Employing 20 race 2-susceptible tomato cultivars, the effect of validamycin A (VMA) treatment on the disease severity (DS) of Fusarium wilt (race 2), salicylic acid (SA) concentration, and plant injury index (PT) was examined. Statistical analysis of the obtained results suggested a negative correlation between the amount of SA and DS without VMA treatment, and between PT and DS with VMA treatment. PT with VMA treatment was positively correlated with the amount of SA with/without VMA treatment. Moreover, the possibility of the rapid screening of plant activators using phytotoxicity as a marker of plant-activator-sensitive cultivars was suggested. The intensity of enhanced systemic acquired resistance (SAR) may depend on the genetic background of each cultivar and its quantity of SAR gene expression.

Functional Analysis of the Validamycin Biosynthetic Gene Cluster and Engineered Production of Validoxylamine A

A 45 kb DNA sequencing analysis from Streptomyces hygroscopicus 5008 involved in validamycin A (VAL-A) biosynthesis revealed 16 structural genes, 2 regulatory genes, 5 genes related transport, transposition/integration or tellurium resistance; another 4 genes had no obvious identity. The VAL-A biosynthetic pathway was proposed, with assignment of the required genetic functions confined to the sequenced region. A cluster of eight reassembled genes was found to support VAL-A synthesis in a heterologous host, S. lividans 1326. In vivo inactivation of the putative glycosyltransferase gene (valG) abolished the final attachment of glucose for VAL production and resulted in accumulation of the VAL-A precursor, validoxylamine, while the normal production of VAL-A could be restored by complementation with valG. The role of valG in the glycosylation of validoxylamine to VAL-A was demonstrated in vitro by enzymatic assay.

Foliar Spray of Validamycin A or Validoxylamine A Controls Tomato Fusarium Wilt

ABSTRACT Tomato wilt, caused by the soilborne fungus Fusarium oxysporum f. sp. lycopersici, is effectively controlled by a foliar spray of validamycin A (VMA) or validoxylamine A (VAA) (>/=10 mug/ml); however, neither VMA nor VAA is antifungal in vitro. In pot tests, the effect of a foliar application of VMA or VAA at 100 mug/ml lasted for 64 days. Plants sprayed with VMA or VAA accumulated salicylic acid and had elevated expression of the systemic acquired resistance (SAR) marker genes P4 (PR-1), Tag (PR-2), and NP24 (PR-5). Foliar spray of VMA also controlled late blight and powdery mildew of tomato. The disease control by VMA and VAA lasted up to 64 days after treatment, was broad spectrum, and induced the expression of PR genes, all essential indicators of SAR, suggesting that VMA and VAA are plant activators. The foliar application of plant activators is a novel control method for soilborne diseases and may provide an economically feasible alternative to soil fumigants such as methyl bromide.

Effective Control of Cabbage Black Rot by Validamycin A and Its Effect on Extracellular Polysaccharide-Production of Xanthomonas campestris pv. campestris

Foliar sprays of validamycin A (VMA) controlled cabbage black rot effectively in pot and field trials. In a pot test, VMA reduced the number of Xanthomonas campestris pv. campestris (Xcc) in leaves. VMA inhibited the production of extracellular polysaccharide (EPS) on yeast-peptone (YP) agar containing carbohydrates. Injection of EPS from Xcc on medium containing VMA produced fewer lesions than that without VMA. These results suggested that VMA might inhibit the multiplication of Xcc in plants and affect the quantity and quality of EPS. © Pesticide Science Society of Japan

Antibacterial Activity of Validamycin A against Pseudomonas solanacearum and Its Efficacy against Tomato Bacterial Wilt.

Validamycin A (VM-A), the active ingredient of Validacin®, inhibits fungal growth by inhibiting trehalase activity. Therefore, VM-A was tested against Pseudomonas solanacearum for its efficacy in controlling tomato bacterial wilt. In media containing trehalose as the sole carbohydrate, VM-A at 50μg/ml inhibited growth of P. solanacearum to rates similar to that of the bacteria in media without carbohydrate for seven days after inoculation. VM-A also gave excellent control of tomato bacterial wilt in greenhouse pot tests, when directly injected into plant stems. In field tests, foliar sprays of VM-A at 250μg/ml five days before and two days after inoculation had reduced disease by 47.4% by four weeks after inoculation. In the tomato stem between 0 and 5cm above the soil line, the bacteria population in the non-treated plot reached 3.84×1010cfu/g fresh weight, whereas that in the VM-A (500μg/ml)-treated plot reached 2.13×109cfu/g fresh weight. Inhibition of bacteria growth by VM-A may delay the appearance of disease symptoms of tomato bacterial wilt.

Effects of Validamycin A on the Growth of and Trehalose Content in Mycelia of Rhizoctonia solani Incubated in a Medium Containing Several Sugars as the Sole Carbon Source.

Trehalose was the main sugar accumulated in the mycelia of Rhizoctonia solani and the trehalose content was 8% and more in dry weight mycelia irrespective of the sugar sources used for incubation. The addition of validamycin A (VM-A), an inhibitor of trehalases, increased the trehalose content even more. The inhibition of growth of the mycelia of R. solani by VM-A occurred when the fungus was incubated in a medium containing trehalose as the sole carbon source but not when incubated in a medium containing various sugars and carbohydrate polymers. The results indicated that trehalose was used as a storage molecule to supply glucose required for growth of R. solani and that the anti-fungal activity of VM-A resulted from the anti-trehalase activity of the chemical.

Studies on glutamine synthetase from Streptomyces hygroscopicus var. jinggangensis.

Streptomyces hygroscopicus var. jinggangensis produces validamycin, an important antibiotic used in agriculture. It was found that there was a positive correlation between the specific activity of mycelial glutamine synthetase (GS) and validamycin biosynthesis in our laboratory. So, in this paper, the purification, characteristics and regulatory properties of GS are reported. The native enzyme had a molecular weight of approximately 530,000 and was composed of 12 identical subunits, each 43,000. Electronic microscopic examination of preparations negatively stained disclosed that the subunits were arranged in two hexagonal rings that lay one on top of the other in a face-to-face fashion. Mg2+ or Mn2+ was absolutely needed as cofactor for GS activity. The enzyme activity was regulated by feedback inhibition and cumulative feedback inhibition. In addition, it was also regulated through a covalent modification, adenylylation and deadenylylation, suggesting that the covalent modification of GS exists not only in Gram-negative bacteria but also in some Gram-positive bacteria.

Validamycin G and validoxylamine G, new members of the validamycins.

Validamycin G and validoxylamine G, new members of the validamycins.

Change in a cell-wall component of Rhizoctonia solani inhibited by validamycin.

Cell-walls prepared from Rhizoctonia solani, cultured with or without validamycin (VM), and fractionated into four fractions (F-I, II, III and IV) by treatment with an alkali or an acid. A quantitative decrease in only cell-wall fraction III (F-III, glycan). i.e., not the other fractions (F-I, F-II and F-IV), due to VM inhibition was observed. The component sugars of individual fractions were investigated by means of acid hydrolysis, methylation analysis, paper chromatography or Smith degradation.From the results, fractions I, II and IV were each assumed to be proteoglycan, free glucose containing oligosaccharides or a chitin, respectively, while fraction III was assumed to be (1→3)-linked glucomannan containing small amounts of pentoses (ribose, arabinose and xylose). With the VM inhibition, the sugar components of the individual fractions, I, II, III and IV, were little affected, but in fraction III the amount of (1→3)-linked glucose or xylose increased, whereas the amount of (1→3)-linked mannose or -ar...

Effect of validamycin A on infection of Rhizoctonia solani in rice sheaths.

Pathological changes of rice sheath tissues caused by Rhizoctonia solani treated with validamycin A (VM-A) was anatomically observed. In sheaths inoculated with mycelial disks after dipping in solutions of 0.63, 1.25, and 2.5ppm VM-A, browning of sheaths and small elliptical spots arose, but no hyphae were observed in the inner space of the sheath. On the other hand, in the lessions formed by inoculation of untreated mycelial disks, abundant hyphae were present in the inner space of the sheaths and the parenchyma cells were severely damaged. Spraying of 10ppm VM-A at 8hr after inoculation of R. solani inhibited the penetration of hyphae into sheath tissues and the browning of sheaths on inoculated part or small elliptical spots were seen on the 4th day. When VM-A was sprayed 16hr after inoculation, hyphae became to be seen in the sheath tissues on the 4th day. Their growth, however, was strikingly inhibited accompanying with little damage of the tissues compared with the lesions formed by the untreated hyphae. The results demonstrate that VM-A is effective against R. solani by both preventing hyphal penetration and retarding its growth.

SYNTHESIS OF 1-O-β-d-GLUCOPYRANOSYL-1l-(1,3,4/2,6)-4-AMINO-6-HYDROXYMETHYL-1,2,3-CYCLOHEXANETRIOL. ON THE STRUCTURE OF THE ANTIBIOTIC, VALIDAMYCIN A

Abstract 1-O-β-d-Glucopyranosyl-1l-(1,3,4/2,6)-4-amino-6-hydroxymethyl-1,2,3-cyclohexanetriol (12) was synthesized and found to be identical with β-d-glucopyranosyl-validamine derived from validamycin A. The position at which validamine moiety was substituted with d-glucopyranose was revised to C-l on the basis of the present synthesis.