amudu: Plant and Animal Viruses

Tuesday, March 24, 2020

Plant and Animal Viruses

INTRODUCTION

Viruses are small obligate intracellular parasites which by definition

contain either a RNA a or DNA genome, surrounded by a protective virus –

coded protein coat.Edward Jenner (1798) introduced the term virus in

microbiology. Virus Greek means ‘’ poison’’. In 1892 for the first time a

Russian botanist DMITRI IWANOWSKI discover the virus. They are infectious and cause various diseases to host organism. They come in different shapes. Based on the types of host cells or organisms, there are different types of viruses as
plant viruses,
animal viruses,
bacteriophages,
fungal viruses,
protists viruses, etc.
However, this article mainly focuses on the difference between plant virus and animal virus.

SHAPE

Viruses are of different shapes such as
spherical or cuboid ( adenovirus),

elongated (potato viruses),
flexuous or coiled (beet yellow),
bullet-shaped (rabies virus),

filamentous ( bacteriophages M13),
pleomorphic.

SIZE

Variable size from 20 nm to 300 nm in diameter. They are smallest than bacteria,

some are slightly larger than protein and nucleic acid molecules and some are

about of the same size ( smallpox virus) as the smallest bacterium and some

virus slightly large (300 – 400 nm).

HELICAL ( CYLINDRICAL) VIRUSES

The helical viruses are elongated, rod-shaped, rigid or flexible. There the capsid is a hollow cylinder with a helical structure. Capsid consists of monomers arranged helically in the rotational axis. The consist may be naked e.g. TMV or envelope e.g. influenza virus.

POLYHEDRAL (ICOSAHEDRAL) VIRUSES

Polyhedral the structure has the three possible symmetries such as

tetrahedral, octahedral and icosahedral.

The viruses are more or less spherical, therefore icosahedral symmetry is

the best one for packaging and bonding of subunits. The cap Somers of each

face form an equatorial triangle and 12 intercepting point or corners.

They consist of naked capsid e.g. adenovirus or envelope e.g. herpes simplex virus.

COMPLEX VIRUSES

The viruses which have the unidentifiable capsids or have the capsids with

additional structures are called complex viruses. Capsids not clearly identified

e.g. vaccinia virus etc. Capsids to which some other the structure is attached

e.g. some bacteriophages etc.

ENVELOPE
There are certain plant and animal viruses and bacteriophage both

icosahedral and helical, which are surrounded by a thin membranous envelope.

This envelope is about 10-15 µm thick.

it is made up of protein, lipids and carbohydrates. Which are combined to form

glycoprotein and lipoprotein? Lipids provide flexibility to the shape, therefore viruses look of variable size and shape. The protein component of the envelope is of viral origin and lipid and carbohydrate may be the feature of the host membrane.

The key difference between plant virus and the animal virus is that the plant virus is an intracellular parasite that infects plants while the animal virus is an intracellular parasite that infects animal tissues.
Plant Viruses

Plant viruses, like other viruses, contain a core of either

DNA or RNA. You have already learned about one of these,

The tobacco mosaic virus.
As plants have a cell wall to protect their cells, these viruses do not use receptor-mediated endocytosis to enter host cells as is seen with animal viruses. For many plant viruses to be transferred from plant to plant, damage to some of the plants’ cells must occur to allow the virus to enter a new host.

This damage is often caused by weather, insects, animals,

fire, or human activities like farming or landscaping. Additionally,

plant offspring may inherit viral diseases from parent plants.

Plant viruses can be transmitted by a variety of vectors,

through contact with an infected plant’s sap, by living organisms such as insects and nematodes, and through pollen.

When plants viruses are transferred between different plants,

this is known as horizontal transmission, and when they are

inherited from a parent, this is called vertical transmission.

Symptoms of viral diseases vary according to the virus and its host (see the table below). One common symptom is hyperplasia, the abnormal proliferation of cells that causes the appearance of plant tumours known as galls.

Other viruses induce hypoplasia, or decreased cell growth,

in the leaves of plants, causing thin, yellow areas to appear.

Still, other viruses affect the plant by directly killing plant cells,

a process is known as cell necrosis. Other symptoms of plant viruses

include malformed leaves, black streaks on the stems of the plants,

altered growth of stems, leaves, or fruits, and ring spots, which are

circular or linear areas of discolouration found in a leaf.

Plant viruses can seriously disrupt crop growth and development, significantly affecting our food supply. They are responsible for poor crop quality and quantity globally and can bring about huge economic losses annually. Others viruses may damage plants used in landscaping. Some viruses that infect agricultural food plants include the name of the plant they infect, such as tomato spotted wilt virus, bean common mosaic virus, and cucumber mosaic virus. In plants used for landscaping, two of the most common viruses are peony ring spot and rose mosaic virus. There are far too many plant viruses to discuss each in detail, but symptoms of bean common mosaic virus result in lowered bean production and stunted, unproductive plants. In the ornamental rose, the rose mosaic disease causes wavy yellow lines and coloured splotches on the leaves of the plant.

Animal Viruses

Animal viruses, unlike the viruses of plants and bacteria, do not

have to penetrate a cell wall to gain access to the host cell.

Non-enveloped or “naked” animal viruses may enter cells in two different ways. As a protein in the viral capsid binds to its receptor

on the host cell, the virus may be taken inside the cell via a

vesicle during the normal cell process of receptor-mediated

endocytosis. An alternative method of cell penetration used by non-enveloped viruses is for capsid proteins to undergo shape changes after binding to the receptor, creating channels in the host cell membrane. The viral genome is then “injected” into the host cell through these channels in a manner analogous to that used by many bacteriophages. Enveloped viruses also

have two ways of entering cells after binding to their receptors:

receptor-mediated endocytosis, or fusion. Many enveloped viruses enter the cell by receptor-mediated endocytosis in a

fashion similar to some non-enveloped viruses. On the other hand,

fusion only occurs with enveloped virions. These viruses, which include HIV among others, use special fusion proteins in their envelopes to cause the envelope to fuse with the plasma membrane of the cell, thus releasing the genome and capsid of the virus into the cell cytoplasm.

After making their proteins and copying their genomes, animal viruses complete the assembly of new viruses and exit the cell. As we have already discussed using the example of HIV, enveloped animal viruses may bud from the cell the membrane as they assemble themselves, taking a piece of

the cell’s plasma membrane in the process. On the other hand, non-enveloped viral progeny, such as rhinoviruses, accumulate in infected cells until there is a signal for lysis or apoptosis and all viruses are released together. Animal viruses are associated with a variety of human diseases.

Some of them follow the classic pattern of acute disease, where symptoms get increasingly worse for a short period followed by the elimination of the virus from the body by the immune system and eventual recovery from the infection. Examples of acute viral

diseases are the common cold and influenza. Other viruses cause long-term chronic infections, such as the virus causing hepatitis C, whereas others, like herpes simplex virus, only cause intermittent

symptoms. Still other viruses, such as human herpesviruses 6 and 7, which in some cases can cause minor childhood disease roseola, often successfully cause productive infections without causing any

symptoms at all in the host, and thus we say these patients have an asymptomatic infection.

In hepatitis C infections, the virus grows and reproduces in liver cells, causing low levels of liver damage.

The damage is so low that infected individuals are often unaware that they are infected, and many infections are detected only

by routine blood work on patients with risk factors such as intravenous drug use. On the other hand, since many of the symptoms of viral diseases are caused by immune responses,

a lack of symptoms is an indication of a weak immune response to the virus. This allows the virus to escape elimination by the immune system and persist in individuals for years, all the while producing low levels of progeny virions in what is known

as a chronic viral disease. Chronic infection of the liver by this

the virus leads to a much greater chance of developing liver cancer,

sometimes as much as 30 years after the initial infection.

As already discussed, the herpes simplex virus can remain in a state of latency in nervous tissue for months, even years.

As the virus “hides” in the tissue and makes few if any viral proteins, there is nothing for the immune response to act against, and immunity to the virus slowly declines.

Under certain conditions, including various types of physical and psychological stress, the latent herpes simplex virus may be reactivated and undergo a lytic replication cycle in the skin, causing the lesions associated with the disease.

Once virions are produced in the skin and viral proteins are synthesized, the immune response is again stimulated and resolves the skin lesions in a few days by destroying viruses in the skin. As a result of this type of replicative cycle, appearances of cold sores and genital herpes outbreaks only occur intermittently,

even though the viruses remain in the nervous tissue for life. Latent infections are common with other herpesviruses as well, including the varicella-zoster virus that causes chickenpox. Some animal-infecting viruses, including the hepatitis C virus discussed above, are known as oncogenic viruses: They have the ability to cause cancer. These viruses interfere with the normal regulation of the host cell cycle either by

either introducing genes that stimulate unregulated cell growth (oncogenes) or by interfering with the expression of genes that inhibit cell growth. Oncogenic viruses can be either DNA or RNA viruses.

Cancers known to be associated with viral infections include cervical cancer caused by human papillomavirus (HPV), liver cancer caused by hepatitis B virus, T-cell leukemia, and several types of lymphoma. HPV, or human papillomavirus, has a naked icosahedral capsid

visible in this transmission electron micrograph and a double-stranded DNA genome that is incorporated into the host DNA. The virus, which is sexually transmitted, is oncogenic and can lead to cervical cancer.

What are the Similarities Between Plant Virus and Animal Virus? Both plant virus and animal virus are intracellular obligate parasites. They live within a host cell. Moreover, they have either DNA or RNA genomes.Both types of viruses cause various diseases.

Furthermore, their genomes can either be single-stranded or double-stranded.

Also, both can either be naked or enveloped.

What is the Difference Between Plant Virus and Animal Virus?