Behaviour of the fungus Rhizoctonia solani Kiihn in the soil

Rhizoctonia solani was found able to grow as a saprophyte through natural unsterilized soil. Its rate of growth under different soil conditions in glass tumblers was studied by the Rossi-Cholodny soil-plate method. Growth was most rapid at the lowest soil-moisture content tested, viz. 30 % saturation, and was accelerated by forced aeration of the soil. The maximum distance to which mycelial growth could be supported on the food reserves of the agar inoculum alone was some 5 cm., as shown by extent of growth through tubes of moist sand, but in 23 days the fungus grew 21–24 cm through tubes of soil. Removal of the agar disk 2 days after inoculation of the tubes reduced growth through sand by more than half, but through soil by only a small proportion. In soil, Rhizoctonia was able to cause 100% damping-off of radish seedlings planted at a radial distance of 4 cm. from the agar inoculum, and some 40 % damping-off at a distance of 9 cm. The depressing effect of additions of 1 % ground-wheat straw or dried grass to the soil upon growth of the fungus was attributed to (1) the negligible cellulose-decomposing ability of Rhizoctonia, (2) nitrogen starvation of the mycelium, through rapid utilization of the available soil nitrogen by the cellulose-decomposing micro-organisms multiplying upon the fresh organic material, (3) fungistatic action on Rhizoctonia of the respiratory carbon dioxide produced by the cellulose-decomposers.     

Expression of the linear DNA plasmid pRS64 in the plant pathogenic fungus Rhizoctonia solani

The plant pathogenic isolate RI-64 of anastomosis group 4 of Rhizoctonia solani possesses three linear DNA plasmids (pRS64-1, -2, and -3). Unique poly(A)^? RNA, 0.5 kb in length and hybridizable with the pRS64 DNAs was found in mycelial cells of the isolate RI-64. The overall homology at the nucleotide level between pRS64-1, -2, and -3, and the cDNA prepared from the poly(A)^? RNA was 100%, 73%, and 84%, respectively. The open reading frames found in pRS64-1, -2, and -3 (ORF1-1, ORF2-1, and ORF3-1) are 68 amino acids long. The amino acids sequence showed no significant homology with known proteins. Extracts from Escherichia coli cells expressing ORF1-1 contain a specific protein of 7 kDa. Antisera raised against the ORF1-1 product obtained from E. coli cells cross-reacted with the specific proteins found in the mycelia. The results indicate that the DNA plasmids found in R. solani contain a sequence that encodes a specific protein which may be involved in determination of plant pathogenicity.     

Recombinant expression and characterization of a l-amino acid oxidase from the fungus Rhizoctonia solani

Applied Microbiology and Biotechnology - l-Amino acid oxidases (L-AAOs) catalyze the oxidative deamination of l-amino acids to the corresponding α-keto acids, ammonia, and hydrogen peroxide....     

Gene expression profiling of the plant pathogenic basidiomycetous fungus Rhizoctonia solani AG 4 reveals putative virulence factors

Rhizoctonia solani is a ubiquitous basidiomycetous soilborne fungal pathogen causing damping-off of seedlings, aerial blights and postharvest diseases. To gain insight into the molecular mechanisms of pathogenesis a global approach based on analysis of expressed sequence tags (ESTs) was undertaken. To get broad gene-expression coverage, two normalized EST libraries were developed from mycelia grown under high nitrogen-induced virulent and low nitrogen/methylglucose-induced hypovirulent conditions. A pilot-scale assessment of gene diversity was made from the sequence analyses of the two libraries. A total of 2280 cDNA clones was sequenced that corresponded to 220 unique sequence sets or clusters (contigs) and 805 singlets, making up a total of 1025 unique genes identified from the two virulence-differentiated cDNA libraries. From the total sequences, 295 genes (38.7%) exhibited strong similarities with genes in public databases and were categorized into 11 functional groups. Approximately 61.3% of the R. solani ESTs have no apparent homologs in publicly available fungal genome databases and are considered unique genes. We have identified several cDNAs with potential roles in fungal pathogenicity, virulence, signal transduction, vegetative incompatibility and mating, drug resistance, lignin degradation, bioremediation and morphological differentiation. A codon-usage table has been formulated based on 14694 R. solani EST codons. Further analysis of ESTs might provide insights into virulence mechanisms of R. solani AG 4 as well as roles of these genes in development, saprophytic colonization and ecological adaptation of this important fungal plant pathogen.     

Acetone Inhibition of Rhizoctonia solani Growth

Acetone (5% v/v) inhibited growth of four isolates of Rhizoctonia solani which differ in their pathogenicity on squash seedlings. Acetone (5% v/v) showed best inhibition on the most aggressive isolate 4 followed by the less aggressive ones (1, 2 and 3, respectively); IAA had no effect on the growth of all R. solani isolates compared to the controls.     

Unique DNA plasmid pRS64 associated with chromosomal DNAs of the plant pathogenic fungus Rhizoctonia solani.

Unique DNA sequences homologous to the linear DNA plasmid pRS64 were investigated in chromosomal DNAs of isolates belonging to anastomosis group 4 (AG-4) of the plant pathogenic fungus Rhizoctonia solani. Chromosome-sized DNAs of isolates RI-64 and 1271 of AG-4 were separated into six bands by orthogonal-field-alternation gel electrophoresis and hybridized to a cloned segment of pRS64. A small chromosome-sized DNA band of approximately 1.1 Mb carried the sequences homologous to pRS64 DNA. Sequences homologous to pRS64 were also maintained within the chromosomal DNA of isolate 127.1 of AG-4 which does not possess the plasmid. The plasmid showed no homology to the mitochondrial DNA of isolate 1271. The possibility that the linear plasmid pRS64 may act as a transposable genetic element is discussed.     

Quantification of mycoparasitism by the nematode-trapping fungus Arthrobotrys oligospora on Rhizoctonia solani and the influence of nutrient levels

Abstract The influence of nutrient level, type of carbon source and nitrogen concentration on the parasitism of Arthrobotrys oligospora on Rhizoctonia solani were investigated by quantification of coiling frequency. Changes in coiling frequency were also compared with changes in hyphal density and colony radial growth rate. Increasing concentrations of corn meal agar gave increasing coiling frequency up to a concentration of half the recomended strength. At higher concentrations the coiling frequency was constant, although the hyphal density of both fungi increased over the whole concentration range. Coiling frequency was positively correlated with the probability of hyphal encounter, calculated as the product of the hyphal densities of the two fungi, except at high CMA concentrations. Amongst several carbohydrates tested, glucose resulted in the highest, and sucrose the lowest, coiling frequency. The effect of the different carbohydrates on coiling frequency was not correlated with the hyphal densities of the fungi. Addition of a nitrogen source, NaNO₃, removed the differences in coiling frequency between glucose and sucrose and increased coiling frequencies on both sugars.     

Study of the aggressiveness of Rhizoctonia solani isolates

This paper presents an in vitro test to screen the pathogenicity of different Rhizoctonia solani isolates on a host range. The level of aggressivity of the different isolates was different for several host plants tested. There were significant differences between the crops and the isolates tested. In general, the disease level was higher on beans, lettuce and cabbage. In carrot and rye grass the level of infection was lower for the isolates of R. solani tested. The potato isolates of R. solani were less aggressive than the isolates coming from maize, fodder beet and sugar beet. The R. solani isolates were also biochemically characterized by pectic zymograms: the isolates Rs0401 (from maize) and Rs0504 (from sugar beet) belong both to the anastomosis group AG2-2.     

Metabolites produced by the phytopathogenic fungus Rhizoctonia solani: isolation, chemical structure determination, syntheses and bioactivity

The isolation, structure determination, syntheses and biological activity of Nb-acetyltryptamine and three proline containing dioxopiperazines, cyclo(S-Pro-S-Leu) (2), cyclo(S-Pro-S-Ile) (3), and cyclo(S-Pro-S-Val) (4), from cultures of Rhizoctonia solani Kuhn are reported here for the first time. Despite the small amounts isolated, the absolute stereochemistry of these naturally occurring dioxopiperazines was established by 1H NMR using for the first time the chiral solvating agent (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol.     

Biotransformation of the phytoalexin camalexin by the phytopathogen Rhizoctonia solani

The unusual metabolism of the cruciferous phytoalexin camalexin by virulent and weakly virulent isolates of the root rot fungus Rhizoctonia solani Kuhn is reported. This biotransformation proceeded via 5-hydroxycamalexin, which was further biotransformed into more polar metabolites. Importantly, the metabolites resulting from transformation of camalexin were significantly less toxic to the pathogen than camalexin. Thus, it was concluded that R. solani can detoxify camalexin through oxidation of the indole ring. The chemistry involved in the structure determination of the intermediates of this pathway, their synthesis as well as antifungal activity is described.     

Improving the Genome Annotation of Rhizoctonia solani Using Proteogenomics

Background Rhizoctonia solani is a pathogenic fungus that causes serious diseases in many crops, including rice, wheat, and soybeans. In crop production, it is very important to understand the pathogenicity of this fungus, which is still elusive. It might be helpful to comprehensively understand its genomic information using different genome annotation strategies.MethodsAiming to improve the genome annotation of R. solani, we performed a proteogenomic study based on the existing data. Based on our study, a total of 1060 newly identified genes, 36 revised genes, 139 single amino acid variants (SAAVs), 8 alternative splicing genes, and diverse post-translational modifications (PTMs) events were identified in R. solani AG3. Further functional annotation on these 1060 newly identified genes was performed through homology analysis with its 5 closest relative fungi.ResultsBased on this, 2 novel candidate pathogenic genes, which might be associated with pathogen-host interaction, were discovered. In addition, in order to increase the reliability and novelty of the newly identified genes in R. solani AG3, 1060 newly identified genes were compared with the newly published available R. solani genome sequences of AG1, AG2, AG4, AG5, AG6, and AG8. There are 490 homologous sequences. We combined the proteogenomic results with the genome alignment results and finally identified 570 novel genes in R. solani.ConclusionThese findings extended R. solani genome annotation and provided a wealth of resources for research on R. solani.     

立枯丝核菌营养菌丝多型性观察

采用了2种不同的方法对立枯丝核菌营养菌丝的形态进行了观察和比较,观察到2种不同的营养菌丝的形态,即菌核类和假分生孢子类。为以后进一步研究立枯丝核菌营养菌丝的多型性奠定了一定的基础。     

Regulation of L-phenylalanine ammonia-lyase from Rhizoctonia solani.

Maximal levels of L-henylalanine ammonia-lyase activity were observed when the mycelial felts of Rhizoctonia solani were grown for 4.5 days on Byrde synthetic medium containing 3.5% glucose and 0.3% L-phenylalanine, Differential centrifugation studies have indicated that the enzyme is localized in the soluble fraction. The time course of induction of L-phenylalanine ammonia-lyase activity by L-phenylalanine showed a lag period of 1 to 1.5 h and reached a maximum around 4 to 6 h after the addition of the inducer to the medium. L-Phenylalanine, L-tyrosine, and L-tryptophan were nearly equally efficient inducers of the enzyme. D-Phenylalanine was as efficient as the L-isomer, whereas D-tyrosine was a poor inducer. Light, gibberellic acid, indole 3-acetic acid, and kinetin had no effect on the induction of L-phenylalanine ammonia-lyase activity. Cycloheximide did not inhibit the uptake of amino acids by the mycelia but completely blocked the incorporation of radioactive amino acids into soluble proteins and the development of L-phenylalanine ammonia-lyase activity. Actinomycin D inhibited both the incorporation of 32P into ribonucleic acid and the enzyme activity. Conclusive evidence for de novo synthesis of L-phenylalanine ammonia-lyase was obtained by the incorporation of radioactive amino acids into the enzyme. Electrophoretic analysis of the purified preparation showed a single protein band that coincided with radioactivity and L-phenylalanine ammonia-lyase activity. Glucose and intermediates of the tricarboxylic acid cycle, like citric acid, alpha-ketoglutaric acid, and succinic acid, and the metabolites of L-phenylalanine, like o-coumaric acid, o-hydroxyphenylacetic acid, and protocatechuic acid, significantly repressed L-phenylalanine ammonia-lyase activity. The observed repression was not relieved by cyclic adenosine 5'-triphosphate.