Electron Microscopy of Maize Rayado Fino Virus in the Internal Organs of Its Leaf hopper Vector

Abstract

Discrete groups of 20- to 25-nm isometric particles, considered to represent maize rayado fino virus (RFV), were consistently observed in the ectoderm, fat body, midgut, follicular cells of the ovary, muscle, and salivary glands of RFV-infected Dalbulus maidis. The particles commonly occurred within cytoplasmic bodies bound by membranes, some of them resembling lysosomes, and were not found in nonviruliferous insects. These findings are congruent with previous studies on the multiplication of RFV in D. maidis. The absence of cytopathologic effects due to viral infection at the ultrastructural level confirms biological data on the absence of deleterious effects of the virus in its vector.

The Two Capsid Proteins of Maize Rayado Fino Virus Contain Common Peptide Sequences

“…Its host range includes both plants and insects [3,4]. Maize (Zea mays L.) is the economically important plant host, and the corn leafhopper (Dalbulus maidis Delong & Wolcott) serves as both a host and the major vector of MRFV [3,4], Recently, Central American (MRFV-CA) and North American (MRFV-TX) isolates of MRFV have been purified and partially characterized by two laboratories [1,2]. MRFV-TX was found to have two prominent capsid proteins [1] whereas MRFV-CA was believed to have one major capsid protein and possibly a minor protein [2].…”

Multiplication of Maize Rayado Fino Virus in the Leafhopper Vector <i>Dalbulus maidis</i>

“…The multiplication of MRFV in D. maidis is not deleterious to the insect as demon strated by the absence of cytopathological effects [12] and alterations in the longevity and reproductive biology of the leafhopper [18,[24][25][26]. This evidence supports the hypo thesis that MRFV and D. maidis have fol lowed a coevolutionary course that resulted in a well-balanced association, in which the parasite does little or no harm to its host [24,25].…”

“…It is possible that restricted passage and failure of MRFV to multiply in the salivary glands of D. ma/ifo determine the inability of many insects to transmit MRFV and the in termittent and erratic pattern of transmission frequently observed in this leafhopper [10,18]. This possibility is supported by the detec tion by electron microscopy of very low con centrations of MRFV in the salivary glands and other organs of D. maidis [7,12].…”

“…Such ability ap peared at first to be associated only with viruses containing relatively large genomes [2], More recently, two viruses with small single-stranded RNA genomes, oat blue dwarf virus [3,4] and maize rayado fino virus (MRFV) [5][6][7], have been shown to multiply in their leafhopper vectors, and are consid ered to represent a new group of plant viruses [2,8,9], That MRFV multiplies in its leafhopper vector, Dalbulus maidis DeLong & Wolcott, was originally suggested by certain charac teristics of the virus-vector relationship, such as the existence of a long incubation period of the virus in the insect, the retention of inoculability by nymphs after moulting, the effect of temperature on transmission, the recovery of virus from viruliferous insects that had lost their ability to transmit, and the lack of effect of abdominal punctures [6,10], Direct evidence of multiplication was re cently provided by the demonstration, us ing enzyme-linked immunosorbent assay (ELISA), of increased virus titers in the bod ies of insects at different intervals after virus acquisition [6,7,11]. The hypothesis of multi plication is supported further by the visuali zation of MRFV particles in the internal or gans of viruliferous D. maidis [7,12], In this paper we examine in more detail the growth of MRFV in ieafhoppers, provid ing additional information on the propaga tive cycle of the virus in its vector. Part of this information was published in abstract form […”

Infectious Maize rayado fino virus from Cloned cDNA

“…The virus induces a fine chlorotic stipple-striping in infected leaves of maize (Zea mays), with virus particles detectable in phloem sieve elements and phloem parenchyma as well as epidermal cells (24). MRFV and other marafiviruses that infect plants in the Poaceae are transmitted in a persistent propagative manner by their leafhopper vectors (25,37), with which they have speciesspecific virus-vector associations (15). MRFV is naturally transmitted by Dalbulus maidis, the corn leafhopper, although it has been experimentally transmitted by D. elimatus, Stirellus bicolor, Baldulus tripsaci, and Graminella nigrifrons (36).…”