Complete nucleotide sequence and genome organization of Beet soilborne mosaic virus, a proposed member of the genus Benyvirus.

The complete nucleotide sequences of RNAs 1 to 4 of Beet soilborne mosaic virus (BSBMV) were determined. The genomic organization of BSBMV is identical to Beet necrotic yellow vein virus (BNYVV), the type species of the genus Benyvirus. BSBMV RNA1 encodes a single large open reading frame (ORF) with similar replicase-associated motifs identified for BNYVV. BSBMV RNA2 has six potential ORFs with an organization resembling BNYVV RNA2. RNA3 and RNA4 resemble the analogous BNYVV RNAs, which encode proteins associated with symptom development and fungal transmission, respectively. The predicted ORFs on BNYVV and BSBMV reveal 23% to 83% amino acid identity and the overall nucleotide sequences are 35% to 77% identical. Based on sequence analyses, BSBMV is a new benyvirus that can be distinguished from BNYVV.

cDNA probes for detection of specific dsRNAs from the fungal pathogen, Monosporascus cannonballus.

Monosporascus cannonballus is an ascomycete fungus that is the causative agent of Monosporascus root rot/vine decline, a serious disease of muskmelon and watermelon. Double-stranded RNA (dsRNA) was identified in approximately 60% of M. cannonballus isolates recovered from infected muskmelon plants in 1993. After repeated laboratory transfer on culture media, the majority of the isolates harboring dsRNAs developed degenerate culture phenotypes and showed reduced virulence (hypovirulence) to muskmelon. Initially, dsRNA purification and cDNA synthesis were attempted in three M. cannonballus isolates harboring dsRNAs. However, numerous difficulties were encountered due to the stable, double-stranded nature of the dsRNAs and contamination of the preparations by fungal rRNA. Several purification and cDNA protocols were evaluated and eventually modified into methods that were ultimately highly effective for cloning dsRNAs from M. cannonballus. The cDNAs derived from purified dsRNA preparations were cloned into a pUC119 plasmid vector and amplified in Escherichia coli. Nine cDNA clones were identified that are specific for medium-sized (ca. 3 kbp) dsRNAs associated with M. cannonballus isolate Ca91-17(96+). The methods used to make the cDNA clones of the dsRNAs in M. cannonballus may be useful for those working on fungal dsRNAs. In addition, these cDNAs may be useful for identifying dsRNAs associated with the hypovirulence phenotype.

A New Virus on Maize in Nigeria: Maize Mild Mottle Virus.

Maize (Zea mays) and itch grass (Rottboellia cochinchinensis) plants exhibiting a mild mosaic or mottle were collected from a farmer's field near Mokwa, Nigeria, in 1993. Icosahedral virions (approximately 28 to 30 nm) were purified from symptomatic tissue by differential centrifugation in 0.1 M phosphate buffer, pH 7.0. The virions are composed of one single-stranded positive-sense RNA of approximately 4,000 nucleotides and, as estimated by 12.5% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), a capsid protein of approximately 28 kDa. The virus was readily detected in infected plants by enzyme-linked immunosorbent assay and immunoblot assays with a polyclonal rabbit antibody derived from purified virions. A partial cDNA library was generated with random primers. Sequence analyses of a cDNA clone representing a portion of the putative replicase gene aligned most closely with related sequences of viruses within the Tombusviridae. In particular, a region of 78 predicted amino acids surrounding the "GDD" replicase motif shares 73% identity with panicum mosaic virus and 61% identity with maize chlorotic mottle virus. The virus is readily transmitted by mechanical inoculation to sweet and dent corn, millet, and wheat. Currently it is not considered of economic importance in Nigeria. The data suggest that "maize mild mottle virus" is a newly identified virus infecting maize.

Development of the otolith organs and semicircular canals in the Japanese red-bellied newt, Cynops pyrrhogaster.

The sequence in which the otoliths and semicircular canals and their associated sensory epithelia appear and develop in the newt are described. Three-dimensional reconstruction of serial sections through the otic vesicle of newt embryos from stages 31 through 58 demonstrate the first appearance, relative position and growth of the otoliths. A single otolith is first seen in stage 33 embryos (approximately 9 days old); this splits into separate utricular and saccular otoliths at stage 40 (13 days). The lateral semicircular canal is the first to appear, at stage 41 (14 days). The anterior and posterior canals appear approximately one week later and the vestibular apparatus is essentially fully formed at stage 58 (approximately 5 weeks). The data reported here will serve as ground-based controls for fertilized newt eggs flown on the International Microgravity Laboratory-2 Space Shuttle flight, to investigate the influence of microgravity on the development of the gravity-sensing organs.