Can plants be infected by viruses? Plant cells are like human or animal cells, they also get infected by viruses and specifically by plant viruses.
These infected plants become a hindrance to the sustainable growth of the plant.
The plant virus affects the plant cells and can be caused due to various reasons like climate change or international movements for trade.
Let us understand how plants get infected and how they cope with the infection. What are the symptoms of an infected plant, what are the causal agents and how crop yields are affected?
1. Can Plants be Infected by Viruses: How do Plants Get Infected?
All kinds of plants whether medicinal or ornamental can be attacked by virus particles. It can even be caused by a normal insect bite.
The whole initiation can be done as easily as the virus reaching just one plant cell. But before multiplication happens, the virus needs to get adapted to the plant’s cells.
This is because viruses do not have any cell machinery of their own to replicate they utilise the host cell’s machinery (the attacked plant in this case) to replicate.
Now the multiple viruses move to the neighbouring cells and continue the molecular mechanisms of virus replication until they reach the plant’s vascular system, which is like the plant counterpart for the circulatory system in animals, after which it can literally infect the entire plant right from the roots to the leaves.
2. Plant Immune Response
Like all other living beings plants also have their own immunity system, so when the plant viruses attack the plant, the plants begin their immune response called gene silencing against the viral infection.
Under this response, the virus gene is considered out of control. So, the plant cells basically cut off the viral RNA into small pieces which turn it off.
Due to the turning off the genetic material can no more replicate which also means that there is no movement or spread of the infection.
Plant biology is very fascinating because an infected plant cell can send a signal to initiate the immune response even before the neighbouring cell is infected thus providing time for the action.
Although this explains the plant’s immunity action, it does not end here. As we have seen that the infected plant uses gene silencing but a special set of proteins is used for this mechanism.
So, the viruses present also have the ability to produce similar proteins which can basically interfere with the plant’s defence mechanism.
It can bind with the receptor site, in place of the immunity-providing cells. Sometimes, it can also modify the site of binding thus enabling the action of the virus over that of the plant.
The systemic infection is not limited to these, the virus infection doesn’t just infect plants but they can produce their own defence attack after they have been attacked by the plant’s immune system.
These counterattacks can be very harmful to the plant as the attack now becomes very focused for example, the search and destroy strategy which involves searching and destroying all the plant proteins which are involved in the defence system.
All of this is very complicated and there are various steps or layers in the process. Even plants have sites and locations for good defence.
They also need to be prepared with plan B always, in case they do not get the preferred path. The coming together of various proteins also helps in creating a better and stronger response.
So, it is basically the play of all these attacks and counterattacks which can help determine the final outcome. It is also affected by the extent of the infection process, genetic resistance and other factors.
3. Plant Viruses
Plant pathogens are different as compared to plant viruses, they are extremely small and can be visualised with an electron microscope and are composed of small pieces of genetic material either DNA or RNA inside a protein coat.
These viruses can be rod-shaped or spherical, based on their coat proteins. Plant viruses can spread by insects, mites, nematodes, fungi, vegetative propagation, seed, pollen and parasitic plants.
4. Different Viral Diseases in Plants
There are different types of plant disease which have varied symptoms like abnormal green mosaic disease, mottling of leaves, necrotic spots, stunting and growth distortion.
A healthy plant can be infected by multiple viruses and this condition of multiple infections can lead to the accumulation of a lot of symptoms, affecting the plant very severely.
4.1. Tobacco Mosaic Virus (TMV)
The infection is spread worldwide, and the spread is quick and wide due to easy adaptability to a lot of hosts.
The symptoms include mosaic patterns of dark and light green areas in infected plants.
It is not transmitted by insects, but usually by people handling infected and non-infected plants simultaneously.
4.2. Cucumber Mosaic Virus (CMV)
The virus has multiple strains and symptoms include stunting, distortion and mosaic on flowers as well as leaves.
Affects a wide variety of plants like Coreopsis, Chrysanthemum, Echinops, Leonotis, and Lobelia.
It is spread by plant-to-plant transmission and by humans handling the plants too.
4.3. Tomato Spotted Wilt Virus (TMWV)
The infected plants show bronzing of the young leaves, which later turn into necrotic spots.
On ripe fruits, you can see blotches and chlorotic spots as well. The host range is very wide, which speaks to why the virus spread so much.
It is spread by various species of thrips and affects the host plants across the globe.
5. Final Thoughts
Plants infected by viruses experience a lot of problems with their molecular biology, the virus movement and molecular virology affect healthy plants working, growth and life overall.
Plant pathologists are trying to derive methods of defence which can be introduced into plants but another problem is that plants do not have any genetic resistance.
Although artificial gene silencing and genome editing are now being used to boost the immune system of plants.