First Report of Brown Ring Patch Caused by Waitea circinata var. circinata on Creeping Bentgrass in Arizona

A disease resembling brown ring (Waitea) patch was observed on a 'Dominant Extreme' creeping bentgrass (Agrostis stolonifera) green on a golf course in Maricopa County, Arizona in February 2010. The green was 17 months old and built with 95% sand and 5% peat moss. The superintendent reported seeing yellow rings, 12 to 16 cm in diameter, on several greens as early as 3 months postinstallation; the yellow rings developed into brown, necrotic rings. Symptoms started in the cool, cloudy, and moist conditions of December (5.0 to 6.7°C) and became persistent into the spring. Symptoms on the samples appeared to be yellowing of leaves and stems with the development of a dark, water-soaked appearance of the whole plant on older affected portions. The samples were incubated in a moist chamber at 22 to 25°C for 24 h. Foliar mycelium developed on the symptomatic leaves, and upon microscopic examination, the mycelium appeared to have the characteristics of Rhizoctonia spp.; i.e., a right-angled branching pattern, constriction of the hyphal branch near its point of origin, and the presence of a septum near the point of origin. The pathogen was recovered from chlorotic tissue by plating the symptomatic tissue on one-quarter-strength acidified potato dextrose agar (9.90 g of PDA and 11.26 g of granulated agar [Fisher, Lenexa, KS] and 600 ml of lactic acid [Sigma, St. Louis, MO] per liter of water) and incubating at ~27°C in light. A Rhizoctonia-like pathogen emerged from the tissue within 48 h and was tentatively identified as Waitea circinata var. circinata based on colony and bulbil morphology after 10 days of incubation (3). The recovered isolate was used for DNA extraction and subsequent amplification and sequencing of the rDNA internally transcribed spacer (ITS) region using ITS1F and ITS4 primers (2). The recovered sequence (HM807352) was compared with the National Center for Biotechnology Information (NCBI) nucleic acid database and was found to show 100% similarity to W. circinata var. circinata (FJ755879). To confirm pathogenicity, the isolate was used to fulfill Koch's postulates. The isolate was grown on autoclaved sand and corn meal (250 g of sand and 50 g of corn meal) for 4 weeks to produce inoculum. Eight grams of colonized sand and corn meal was broadcast on 4-week-old creeping bentgrass seedlings ('Penncross') planted in a 90:10 peat moss/sand mixture in 10-cm-diameter pots. There were three replications and the experiment was repeated twice. Negative controls consisted of plants inoculated with sand and corn meal only. Pots were maintained at 28 to 33°C in the greenhouse with ambient light. Within 4 days of inoculation, the plants showed chlorosis and necrosis, while noninoculated plants showed no symptoms. The pathogen was successfully reisolated from several plants from each replication using the method described above. This pathogen has been known to cause disease on annual and rough bluegrass (1,2) in the United States, but not confirmed as a pathogen on creeping bentgrass here. To our knowledge, this is the first report of brown ring patch on creeping bentgrass in Arizona. References: (1) C. M. Chen et al. Plant Dis. 91:1687, 2007. (2) K. de la Cerda et al. Plant Dis. 91:791, 2007. (3) T. Toda et al. Plant Dis. 89:536, 2005.

Identification of the regions of Fv1 necessary for murine leukemia virus restriction

The Fv1 gene restricts murine leukemia virus replication via an interaction with the viral capsid protein. To study this interaction, a number of mutations, including a series of N-terminal and C-terminal deletions, internal deletions, and a number of single-amino-acid substitutions, were introduced into the n and b alleles of the Fv1 gene and the effects of these changes on virus restriction were measured. A significant fraction of the Fv1 protein was not required for restriction; however, retention of an intact major homology region as well as of domains toward the N and C termini was essential. Binding specificity appeared to be a combinatorial property of a number of residues within the C-terminal portion of Fv1.

A conserved mechanism of retrovirus restriction in mammals

The murine Fv1 gene restricts infection by N- or B-tropic murine leukemia viruses at a postentry, preintegration stage. The Fv1-sensitive viruses previously used for the study of Fv1 encode an ecotropic envelope gene and thus only infect rodent cells. Consequently, the study of Fv1 restriction has been carried out solely in mice and murine cell lines. By infection with retroviral vectors containing N- or B-tropic core and pantropic vesicular stomatitis virus-G envelope protein, we now demonstrate that cell lines derived from various mammalian species, including humans, have an Fv1-like retrovirus restriction function, preventing N-tropic vector infection. Like Fv1, restriction is directed at amino acid 110 of the viral capsid protein. In contrast to Fv1, the novel restriction is characterized by the absence of reverse-transcribed viral DNA. We speculate that these activities have been selected for by retroviral epidemics in the distant past.

Use of a transient assay for studying the genetic determinants of Fv1 restriction

To probe the genetic determinants controlling the interaction between the retroviral restriction gene Fv1 and its murine leukemia virus target, we set out to develop rapid, transient assays for Fv1 function. Cells were transfected or transduced with Fv1 expression plasmids which can produce green fluorescent protein via an internal ribosome entry site positioned between the Fv1 and green fluorescent protein coding sequences. Fv1 function was then assessed by comparing virus replication in green fluorescent protein-positive and -negative cells, using retroviral vectors encoding a second fluorescent marker, yellow fluorescent protein, or beta-galactosidase. Using this assay, we could show that Fv1 specificities were not as absolute as previously thought, since the Fv1(b) allele was capable of interacting with "nonrestricted" B- and NB-tropic viruses and by shuffling the n- and b-alleles of Fv1, it was possible to generate a Fv1 molecule capable of restricting N-, B-, and NB-tropic viruses equally efficiently. Further, we could show that the presence of nonrestricting Fv1 in the same cell as restrictive Fv1 abrogates restriction, implying competition for binding to the retroviral target.

Positional cloning of the mouse retrovirus restriction gene Fv1

Vertebrate evolution has taken place against a background of constant retrovirus infection, and much of the mammalian genome consists of endogenous retrovirus-like elements. Several host genes have evolved to control retrovirus replication, including Friend-virus-susceptibility-1, Fv1, on mouse chromosome 4 (refs 3, 4). The Fv1 gene acts on murine leukaemia virus at a stage after entry into the target cell but before integration and formation of the provirus. Although restriction is not absolute, Fv1 prevents or delays spontaneous or experimentally induced viral tumours. In vitro, Fv1 restriction leads to an apparent 50-1,000 fold reduction in viral titre. Genetic evidence implicates a direct interaction between the Fv1 gene product and a component of the viral preintegration complex, the capsid protein CA (refs 7-9). We have now cloned Fv1: the gene appears to be derived from the gag region of an endogenous retrovirus unrelated to murine leukaemia virus, implying that the Fv1 protein and its target may share functional similarities despite the absence of nucleotide-sequence homology.

Retinoic acid inhibits both the basal activity and phorbol ester-mediated activation of the HIV long terminal repeat promoter

OBJECTIVE

To establish whether the steroid hormone retinoic acid (RA) was able to modulate the activity of the HIV-1 promoter.

DESIGN

The effect of RA and nuclear factor (NF)-kappa B on HIV-1 promoter activity was investigated using HIV-1 long terminal repeat (LTR)-based reporter constructs.

METHODS

The activity of wild type and mutant LTR sequences was compared in a variety of stably and transiently transfected human cell lines.

RESULTS

It was shown that RA treatment inhibits both the basal activity of the HIV-1 LTR and its stimulation by phorbol ester treatment. This inhibition is observed in both HeLa cells (in the presence of exogenously supplied RA receptors) and the naturally RA-responsive U937 monocyte cell line. RA can also inhibit the stimulation of the HIV-1 LTR by overexpression of NF-kappa B subunits, while linkage of the NF-kappa B sites in the HIV promoter to a heterologous promoter results in its inhibition by RA.

CONCLUSIONS

The data presented clearly demonstrate a negative effect of RA on HIV-1 LTR activity that may contribute to its effect on viral replication.