Plant virus

mic281 general virology V* Plant Virus Description Inside: Plant viruses face special problems initiating an Examples • P2 infection. The outer surfaces of plants are Transmission • P3 composed of protective layers of waxes and pectin, but more significantly, each cell is surrounded by a thick wall of cellulose overlying the cytoplasmic membrane. No plant virus is known to use a specific cellular receptor of the type that animal and bacterial viruses use to attach to cells.

Entry of viruses Plant viruses rely on a mechanical breach of the integrity of a cell wall to directly introduce a virus particle into a cell. This is achieved either by the vector associated with transmission of the virus or simply by mechanical damage to cells. RNA Viruses - Class IV (+ sense) ssRNA Examples Family Potyviridae OF PLANT VIRUSES (Genus Potyvirus) - potato virus Y - papaya ringspot virus (PRSV) Family Flexiviridae - potato virus X Family Comoviridae - cowpea mosaic virus (Genus Tobamovirus) - tobacco mosaic virus Family Sequiviridae - Plant virus Genus Waikavirus – rice tungro spherical virus page 2 mic281 general virology

Transmission OF PLANT VIRUS Sap: Sap is a fluid transported in xylem cells or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant. Seeds: due to external contamination of the seed with virus particles, or due to infection of the living tissues of the embryo. Vectors: Many different groups of living organisms can act as vectors and spread viruses from one plant to another: Bacteria - (e.g. Agrobacterium tumefaciens - the Ti plasmid of this organism has been used experimentally to transmit virus genomes between plants) Fungi Nematodes Arthropods - Insects - aphids, leafhoppers, planthoppers, beetles, thrips, etc. Arachnids - mites Mechanical: Mechanical transmission of viruses is the most widely used method for experimental infection of plants and is usually achieved by rubbing virus- containing preparations into the leaves, which in most plant species are particularly susceptible to infection. However, this is also an important natural method of transmission. Virus particles may contaminate soil for long periods and may be transmitted to the leaves of new host plants as wind-blown dust or as rain-splashed mud. page 3 mic281 general virology